Water temp fluctuates; how much is considered “normal”?

[LarryM]

My E24’s operating temp varies from the gage's 10:00-1:00 positions, depending on the load. It’s stable at idle and normal cruising, but when going up a long, 7% grade near my home on a warm (~85 degree) day it moves into the 1:00 position. The car runs great and never overheats, but this temperature variation is something I’ve never noticed before. (However, we ARE having a relatively hot, humid summer this year.)

I recently installed a new Behr radiator and the correct Wahler 80 degree t-stat along with all new hoses. The fan clutch is relatively new and working. The symptoms tell me it’s air trapped in the system. I’ve bled it several times including trying all the tricks of “burping” it with the front end raised, etc. but I don’t see any air coming out at all. I'm kinda stumped.

Conversely, my E28’s temp is always between 10:00-11:30 and seems much more stable. That car is originally from TX and I’m speculating the PO may have installed a lower, 71 degree t-stat in an effort to achieve cooler running in the Dallas heat.

I do believe I’ve gotten all the air out of the E24’s system but am open to any suggestions. How much variation in operating temperature is acceptable? Would it be worth trying out a 71 degree t-stat, even though it's not "correct"?

[LeiseyJr]

Its normal, its why BMW ended up buffering the gauges in the 90’s so the temps stay exactly at middle.

[Mike W.]

No, I would say not normal. In town, absolutely. But on the road in very moderate condtions, 85F, it should be stable. Assuming it's a new radiator and not a new to you radiator, I've seen somewhat plugged ones that would run warm on the highway, but that was a bad radiator. Humidity means nothing to the car, you and I will feel it, but the car doesn't care about it and running hot. As you well know, later E24s and E28s are twins under the skin, er sheetmetal. With a good used radiator my E28 didn't get over halfway on the highway, even in 113F temps. It's not trapped air, if you get it bled enough it warms up like it should and the heater works, it will self bleed any remaining air. Slight caveat, if the coolant tank up top has a crimped line on the little hose up top you can get some odd stuff going on. There's supposed to be a metal sleeve inside it, but if it's missing you can crank down on the hose clamp enough to pinch it shut. That will create problems. I have seen sticky thermostats, but they usually spike on warmup but are ok after that.

Now E28s aren't as prone to it as earlier BMWs, and I consider a later E24 an E28, but BMW temp gauges are super sensitive to grounds. I had an early E24, an '80, years ago that always seemed to run hot in spite of a recored radiator. Never overheated, but it spent considerable time above the halfway point. Turned out to be a bad ground, when I ran an extra one between the engine and the body all of the sudden it was dead solid in the 3/8 to 7/16 range. All the testing and troubleshooting and time and energy and all it took was a two foot piece of #12 wire to fix it.

Don't forget about test tools, with the price of infared "gun" thermometers these days there's no excuse not to have one in your situation. $25 or less now.

[brickwhite]

[tschultz]

195F should only be seen in sitting stop and go traffic on 95F days. If it creeps up to that point in normal driving, time to look at fan clutch, thermostat, radiator, belt tightness. Verify Aux fan switches on at these speeds...

It is possible your sender is a little bit out of calibration or has a bad ground as Dave suggests.

In normal use, the gauge should not be straight vertical. I like it because you know actual temperature before it is 205+...

[harrypalmer]

Basically I did the same as LarryM (RR new rad, all hoses, OEM 80° T-tat, plus 82°and 91°switches respectively on my E28) in my case, before the install my car's temp would creep a bit into the 11:15 hour if I climbed steadily up on a mountain highway at say, 75mph in fourth gear, but once eased off in fifth gear the temp gauge needle would come down and stay at 10:30 or 180F degrees. The same holds true after install but the average temp is decidedly much lower, however...
Before...
After...

While cruising the car is a champ but when it hits traffic the car's engine seems to get really hot (gauge needle stays lower than 11:30 nonetheless but engine starts to hesitate, almost to the point of cutting off power, please see 4 sec video here https://ci-44111562222-4b464fa7.http.at ... 075ef403d4

However, the temp needle will not creep up and stays planted at 11:30 but all the hoses are extremely hot at the touch. Please see link to pics of different cooling hoses and parts here https://www.flickr.com/photos/109547372@N04/page4

Here's a pic of the outside temp (which tells me is not correct) but indicates the approximate heat around the engine bay area.


So my question begs, is it normal for this temperature fluctuation and in my car's case what can I do to solve the heating/bucking of the engine? Thank you all.
LarryM please forgive me for highjack your thread. I'll remove my stuff to a new post if you like.

[LarryM]

Thanks for the info! Before I do any more testing I'm going to check the grounds. I recently had a manual swap completed on the car and maybe one was not reattached. Where should I be looking? Are there any that should be connected between the tranny and the frame?

Other than that, I'm thinking that poor coolant flow is the problem, since it only gets warm at speed, uphill and under load.

The Behr radiator is brand new. I replaced my old radiator (for an automatic tranny) with a new one (for a manual). One possibility I thought of, is that maybe I happened to get a "bad" one with restricted passages. How likely is that?

The coolant tank is new, too. I'll check to see if that tiny metal sleeve is in there.

I'll also check to see that the auxiliary fan switches are working; I've heard they can go bad. But as I said, the problem doesn't seem to be airflow.

I do have an infrared thermometer from Harbor Freight; I just hope it's reasonably accurate.

[LarryM]

I just started my car cold, with a piece of cardboard in front of the radiator to monitor what's going on.

At what temperature is the fan clutch supposed to engage? I just noticed that on a cold start, mine (a 20 year-old Sachs unit with about 20K miles) doesn't lock up until at least the 1:00 position, or about 200-205 degrees F. Once it's engaged, it remains locked up even after the temp comes back down to the 11:00 position, or about 190 degrees.

Does this indicate a lazy or weak fan clutch?

Everything else (including function of auxiliary fan) checks out OK.

[JohnH]

The fan clutch isnt temperature dependent. It is a viscus coupling designed to restrict fan speed at higher engine rpm.

If its not engaging at startup, the clutch oil has run out.

Toyota uses a similar fan clutch. Do a google search on "toyota fan clutch oil" for details on repairing your fan clutch.

I agree with MikeW, you have coolant circulation problems. You say you replaced the rad, but what about the pump? If so did it have a plastic or metal impeller? If plastic, they are known to slip as I can attest to on my old 325tds.

[Mike W.]

Thanks for the info! Before I do any more testing I'm going to check the grounds. I recently had a manual swap completed on the car and maybe one was not reattached. Where should I be looking? Are there any that should be connected between the tranny and the frame?

Other than that, I'm thinking that poor coolant flow is the problem, since it only gets warm at speed, uphill and under load.

The Behr radiator is brand new. I replaced my old radiator (for an automatic tranny) with a new one (for a manual). One possibility I thought of, is that maybe I happened to get a "bad" one with restricted passages. How likely is that?

The coolant tank is new, too. I'll check to see if that tiny metal sleeve is in there.

I'll also check to see that the auxiliary fan switches are working; I've heard they can go bad. But as I said, the problem doesn't seem to be airflow.

I do have an infrared thermometer from Harbor Freight; I just hope it's reasonably accurate.

Aux fan shouldn't be needed at 85F on the road. HF thermometer doesn't have to be that accurate, you're looking for changes and hot spots.

The fan clutch isnt temperature dependent. It is a viscus coupling designed to restrict fan speed at higher engine rpm.

On the contrary. Early ones, in the BMW world the bolt on clutches, instead of the screw on that E28s use were as you describe, but the screw ons are most definitely temp dependent.

[LarryM]

I decided to order a new Sachs fan clutch and see if it helps. The one on my E28 is newer and seems to lock up much earlier; maybe that's the reason that car seems to run much cooler and at more stable temps than my E24. Anyway, it's an easy R&R and worth a try.

My E24 has a water pump from Bav Auto which I installed 20 years ago; I'm not sure of the brand, but I do know it has a metal impeller. It has only about 20K miles on it so I'd be surprised if it's failed already. But, it's still a possibility.

[jhh925]

Before I do any more testing I'm going to check the grounds. I recently had a manual swap completed on the car and maybe one was not reattached. Where should I be looking? Are there any that should be connected between the tranny and the frame?

Not sure if this question was answered.

There are two main ground straps, one connects the block to the frame rail: block connection is on the passenger side, right behind the AC compressor and directly beneath the #2 cylinder exhaust port (or maybe roughly between the #2 and #3 ports), frame attachment is just outboard of that on the top of the frame rail. The second connects the head to the firewall: head connection is at the valve cover nut, far rear corner on the passenger side, attaching to the firewall immediately behind that.

There are multiple ground connector collection points. The two main ones that I'm aware of are on the fender wall right above the battery negative terminal, and one deep in the dash on the frame member where the rear-most steering column attaching point is (basically right behind the cluster). There may be others, but I don't have them top of mind.

[LarryM]

Thank you for that info about the ground connections, jhh925.

[gaberdee]

I wonder if Behr has a bad batch of radiators out there.

I’m experiencing similar symptoms. I recently replaced the radiator, water pump, thermostat, hoses, fan clutch and am running bmw coolant. Under load the temp gauge moves to 1:00 sometimes even 1:30, whereas with my previous behr radiator (which sprang a leak in July) the temp gauge was never past 11, even in gridlocked NYC summer traffic, with heat radiating off the pavement like a frying pan.

I’ve drained the coolant twice and flushed to check for blockages, I’ve replaced the t-stat twice, and I’ve swapped out the temp sensor. I’ve also replaced the fan clutch, which was new last summer and passed the newspaper test. I’m ready to pull my hair out.

The one thing I haven’t done is check the engine bay with an infrared thermometer, which is next on my list. I have however checked and cleaned the grounds, which are fine, and I was also planning on swapping in another cluster to check the gauge.

Vince G. mentioned in a separate thread that he bought two behr radiators in a row that had leaks, which got me thinking maybe the radiator is the problem. http://www.mye28.com/viewtopic.php?f=2& ... r#p1450452

Who knows if they’re related. At this point I don’t know what else it could be. I’d be interested to know when your radiator was manufactured. I just checked the date stamp on my radiator and it’s 10/14/2017

Cheers,
Gabe

[LarryM]

Gabe,

My radiator is also stamped 10/14/2017. I bought a Behr because some of the more knowledgeable forum members felt they were preferable over Nissens. Mine is manufactured in South Africa, which is also supposed to be desirable. I bought it from Autohaus AZ earlier this year.

I just went through an issue with several leaking, brand new heater valves from BMW. Behr is supposed to be an OE supplier to BMW. If this overheating issue turns out to be a bad radiator, it's not going to reflect very well on the general quality of replacement parts we're getting for our cars...even those from the more reputable manufacturers.

Since our cars both run hotter than normal under load, it would possibly point to a radiator with restricted flow or insufficient cooling ability. We can check the input and output temps of our radiators with an infrared thermometer at idle, but that won't tell us how efficiently they're cooling when there's a demand for greater water volume flowing through them under load, at speed. Still worth checking though. What are the input and output temps supposed to be at idle?

[HayekFan]

Definitely check the grounds. I recently solved similar symptoms in my '86 E28 by cleaning and retightening the ground connection between the block and frame down by the exhaust manifold.

I had read about the possibility of grounds being the culprit but was skeptical because my temp fluctuations tracked so directly with engine load. When climbing a long hill it would creep up past the halfway point and then drop back to normal on the downhill side. It seemed for sure like a basic cooling system problem, but nope, after being stumped for a while it was the ground that got it.

[gaberdee]

Here’s a quick update for the OP.

I’ve finally had a chance to get an infrared thermometer and my engine is in fact not running warm. With the needle at 12:30 to 1:00 my engine temp reads right around 178-180. This is with the thermometer pointed at the top of the thermostat housing, where the temp sender is. So I guess my new Behr radiator is fine after all.

I’ve checked and cleaned every ground at least three times at this point, though I’m not sure what else it could be. Not sure if I mentioned it or not but this is in addition to swapping out the temp sender for a known good one. I have a spare cluster stashed at my parents’ house. Next time I’m there I’ll see if that’s the culprit.

In any case, hope you’ve resolved this issue by now.

Cheers,
Gabe

[harrypalmer]

Aux fan shouldn't be needed at 85F on the road. HF thermometer doesn't have to be that accurate, you're looking for changes and hot spots.

To follow your quote here, what you would consider hot spots and where to look for?

With an infrared thermometer I have caught the following temp readings on two separate occasions immediately after the car was shut off, and the needle did not move past eleven thirty.
The upper hose it still feels darn hot to the touch and don't know what to make of it and these recorded temps.
And only once I have heard / seen the aux fan working while I was parked and no AC running.

Top of Radiator: 191°F / 187°F

Exit of Little Hose to Coolant Reservoir: 190°F / 187°F

Coolant Reservoir: 165°F / 175°F

Upper Radiator Hose: 187°F / 183°F

Thermo (Blue) Switch: 182°F / 190°F / 172°F

Thermo (Brown) Switch: 187°F / 175°F

Thermo (Black) Valve: 163°F / 176°F

Thermostat Housing: 178°F / 177°F

Hose to Thermostat: 189°F / 184°F

Hose to Water Pump: 189°F / 194°F

Radiator Thermos Switches: 169°F / 154°F

Upper (passenger) side of Radiator: 159°F / 180°F

Lower side of Radiator: 136°F / 141°F

Fuel Tank: 126°F / 125°F

Gas Cap: 118°F / 112°F

Inside Trunk: 108°F / 104°F

Rear Exhaust: 243°F / 238°F

Inside Rear Exhaust Pipes: 351°F / 335°F

[Blue Shadow]

Good list but it would help to have the ambient temperature, altitude and barometric pressure to allow improve the data collection. Altitude if you were a mile high or so when this was done and ambient temp would be most important.

[harrypalmer]

Good list but it would help to have the ambient temperature, altitude and barometric pressure to allow improve the data collection. Altitude if you were a mile high or so when this was done and ambient temp would be most important.

Great point!

Altitude: 5293 feet for both ambient temp readings: July 1st / August 11th

88°F / 86°F

Barometric Pressure: 29.86 "Hg / 29.97 "Hg

Humidity: 29% for both dates

First reading was made with older and in good condition (less than two years old 80° Thermostat)
Second reading was obtained with both all new 80° OEM Thermostat and hoses

Still, no idea what to do with all this data but I've got a strong feeling you DO and specially how to evaluate all of this. So thank you.
I'm suspicious (in my ignorance) that my rattling-when-hot 32 year old catalytic converter maybe a partial culprit of affecting coolant temperatures all around as well? And lastly, I have checked in multiple occasions that I don't have any coolant loss or leaks

[Mike W.]

Those temps don't look all that hot, but then again in mild weather with the A/C off the Aux fan shouldn't be coming on. But that's good in a way, it means water is circulating, I've had BMWs where they were hot the but fan didn't come on because the radiator was restricted and the coolant was cool by the time it passed thru the radiator, just not enough of it did.

I'm at a loss right now, sorry.

[harrypalmer]

Those temps don't look all that hot, but then again in mild weather with the A/C off the Aux fan shouldn't be coming on. But that's good in a way, it means water is circulating, I've had BMWs where they were hot the but fan didn't come on because the radiator was restricted and the coolant was cool by the time it passed thru the radiator, just not enough of it did.

I'm at a loss right now, sorry.

Hey Mike, don't be. But if you are, guess how I feel Either way I thank you for your reply. I guess everything is fine but my gut feeling tells me the upper hose should be less hot to the touch and that affects whatever I've got left of my neurons

[Mike W.]

The upper hose should be hot. The stat is trying to make it hot. It's a little tricky to get in there, but try shooting different parts of the radiator core itself. If some are hot and some tubes are cold, the cold ones don't have flow. Or just stick your hand in there after you shut it off. It should be cooler on the return side of course, but if you have areas that are hot and some that are cold that could be your problem.

[harrypalmer]

The upper hose should be hot. The stat is trying to make it hot. It's a little tricky to get in there, but try shooting different parts of the radiator core itself. If some are hot and some tubes are cold, the cold ones don't have flow. Or just stick your hand in there after you shut it off. It should be cooler on the return side of course, but if you have areas that are hot and some that are cold that could be your problem.

I have taken snapshots of recently installed new Behr radiator at all four corners and both the return below and the top (passenger side) are colder than say, the hotter top and bottom of (driver's side) as I guess they should be. I'll take some readings from various points as you suggest and will get back with precise readings. Thanks

[LarryM]

I’m the OP with an update.

So I decided to purchase a new radiator and thermostat from a BMW dealer (Husker). What I discovered was, there are indeed some differences between a BMW-branded radiator (made by Behr in Germany) and a Behr radiator (made in South Africa) sold through retailers.

The BMW radiator uses 45 “flattened” coolant tubes running crossways, while the Behr uses 25 either round or oval (hard to tell) tubes, in each row. I don’t know how many rows there are in each radiator; I assume 2 or 3. But it does appear that the BMW radiator’s core has more surface area and I would thereby assume it’s more efficient for heat transfer.

The plastic used in the header tanks on each one is different. The BMW’s tanks have a rougher texture, while the Behr’s are smooth. I’ve read that some radiator manufacturers have been using recycled plastic but I have no idea how to tell by appearance and feel.

Also, the header tanks on the BMW radiator are crimped as well as bonded; the Behr’s are simply bonded. The BMW’s appears to be more costly to manufacture, but more rugged.

So I drove my car today with the new “genuine” BMW radiator and BMW thermostat, and took some readings with an infrared thermometer. (Note that the ambient temp today is about 80*F, whereas it was about 85*F last time I drove it.) The temp gauge still fluctuates somewhat under different driving conditions, but it stays between 10:00 and 11:30 and never goes beyond the 12:00 position. Previously, with the Behr radiator, it would sometimes go beyond 12:00 and approach 1:00 while under load, going uphill on a long grade. My readings on the radiator, thermostat housing, hoses, etc. confirm it’s now running about 10*F cooler than before. I feel this is about where it should be.

BTW, the BMW-branded t-stat (made by Wahler) appears to be virtually identical (aside from the “BMW” logo) to the Wahler t-stat I removed. I tested both of them in hot water and they perform the same. So don’t waste your money by paying extra for one of these at a dealer.

I took some comparison pics of the BMW and Behr radiators and will post them if I can figure out how.

[harrypalmer]

I’m the OP with an update.

So I decided to purchase a new radiator and thermostat from a BMW dealer (Husker). What I discovered was, there are indeed some differences between a BMW-branded radiator (made by Behr in Germany) and a Behr radiator (made in South Africa) sold through retailers.

The BMW radiator uses 45 “flattened” coolant tubes running crossways, while the Behr uses 25 either round or oval (hard to tell) tubes, in each row. I don’t know how many rows there are in each radiator; I assume 2 or 3. But it does appear that the BMW radiator’s core has more surface area and I would thereby assume it’s more efficient for heat transfer.

The plastic used in the header tanks on each one is different. The BMW’s tanks have a rougher texture, while the Behr’s are smooth. I’ve read that some radiator manufacturers have been using recycled plastic but I have no idea how to tell by appearance and feel.

Also, the header tanks on the BMW radiator are crimped as well as bonded; the Behr’s are simply bonded. The BMW’s appears to be more costly to manufacture, but more rugged.

So I drove my car today with the new “genuine” BMW radiator and BMW thermostat, and took some readings with an infrared thermometer. (Note that the ambient temp today is about 80*F, whereas it was about 85*F last time I drove it.) The temp gauge still fluctuates somewhat under different driving conditions, but it stays between 10:00 and 11:30 and never goes beyond the 12:00 position. Previously, with the Behr radiator, it would sometimes go beyond 12:00 and approach 1:00 while under load, going uphill on a long grade. My readings on the radiator, thermostat housing, hoses, etc. confirm it’s now running about 10*F cooler than before. I feel this is about where it should be.

BTW, the BMW-branded t-stat (made by Wahler) appears to be virtually identical (aside from the “BMW” logo) to the Wahler t-stat I removed. I tested both of them in hot water and they perform the same. So don’t waste your money by paying extra for one of these at a dealer.

I took some comparison pics of the BMW and Behr radiators and will post them if I can figure out how.

If you are on a Mac I could show you how to upload pictures relatively easy if you like. Otherwise here's a link on the subject http://www.mye28.com/viewtopic.php?f=1&t=147488 I am glad your temps are lower. Just like you did, I discovered after the fact, the same on the Wahler thermostat and thus wasted my money.
-Jack

[Mike W.]

Pull up a chair, this could be a while.

Radiators.

The round tube ones have been around for at least 15 years. I think E28 heater cores are round tube. Are flat tubes better than round ones? Or is Behr just making a part to 1980s BMW spec? I dunno. I've heard the round tube also have spirals in them to promote turbulence so you don't get stratification and do get maximum cooling. It's a complicated equation that my high school physics didn't cover.

Larger tubes seem to be better for higher speeds. I had a Bav with a recored radiator with only 28? rows, but 50%(?) fatter tubes. Flat ones. It obviously flowed a lot better. It was marginal in town with the A/C on, but never budged on the highway. Uphill, A/C on, 110F outside? Gauge didn't move. More recent Behr radiators for E28s I've seen seem to have been around 38 tubes, flat. I did have one 50 tube for a E23, same height as E28 but a touch longer. Might have been Nissens, maybe not. It didn't run hot, but no A/C on that car so not much of a test, although it's predecessor did start moving up at speeds over about 65. But that one was only about 30 flat tubes. I had an E12 with 32(?) tubes, old, that wasn't bad in town even in Vegas August with the A/C on, but didn't like it on the highway over about 65.

So. Better flow is definitely better on the highway at higher speeds. But in town surface area seems to be more important. More tubes meaning more surface area. But it's got to be capable of flow too. Like a lot of things in life it's a compromise.

[harrypalmer]

Pull up a chair, this could be a while.

Radiators.

The round tube ones have been around for at least 15 years. I think E28 heater cores are round tube. Are flat tubes better than round ones? Or is Behr just making a part to 1980s BMW spec? I dunno. I've heard the round tube also have spirals in them to promote turbulence so you don't get stratification and do get maximum cooling. It's a complicated equation that my high school physics didn't cover.

Larger tubes seem to be better for higher speeds. I had a Bav with a recored radiator with only 28? rows, but 50%(?) fatter tubes. Flat ones. It obviously flowed a lot better. It was marginal in town with the A/C on, but never budged on the highway. Uphill, A/C on, 110F outside? Gauge didn't move. More recent Behr radiators for E28s I've seen seem to have been around 38 tubes, flat. I did have one 50 tube for a E23, same height as E28 but a touch longer. Might have been Nissens, maybe not. It didn't run hot, but no A/C on that car so not much of a test, although it's predecessor did start moving up at speeds over about 65. But that one was only about 30 flat tubes. I had an E12 with 32(?) tubes, old, that wasn't bad in town even in Vegas August with the A/C on, but didn't like it on the highway over about 65.

So. Better flow is definitely better on the highway at higher speeds. But in town surface area seems to be more important. More tubes meaning more surface area. But it's got to be capable of flow too. Like a lot of things in life it's a compromise.

Mike,
Just read your first line and wanted to grab that seat next to you and hear you talking Radiators while having a glass of wine. So here's to you Sir, maybe someday. BTW about the spirals, you heard that right too. Here they are: