Engine Overheating

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Jcat
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Engine Overheating

Post by Jcat »

I just finished a 3 hour ride from Birmingham to Atlanta in a hot-boxed car. Outside temp is 82F. I dont think my aux fan is kicking on. How can I test it. I suppose I can run the car to above the center line on the temp gauge again and jump out of the car to see if the fan is on or not. Any thoughts on this? My A/c system was completely rebuilt be an a/c shop that I trust. That was last year. It was super this year, but then again, I had not been on back to back 3hr trips (I drive to AL yesterday) for maybe 10 years or more in that car. I need to take drastic measures, I believe, to get the engine to run cooler in this hot GA climate. Do you think the best move (once I have whatever is broken replaced) would be to install an oversized radiator of some sort... say E28 aluminum? Let me know your thoughts. I'm really bummed.... BTW... car does not overheat as much when a/c is not running, but it does get hotter than it should.
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528i-1981
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Re: Engine Overheating

Post by 528i-1981 »

Hi Jay - the aux fan is loud, and you should definitely hear it when the AC is on when still and at idle. There are two thermostats that come into play, which area discussed in other threads.

https://www.firstfives.org/phpBB-3.2.1/ ... hp?p=29016

Robert's cooling system FAQ also covers the general layout. You can test for power at the aux fan plug pretty easily after removing the grilles. It should come on when the AC is switched on. But again, there's no question when it's on - it's loud and you can see it turning.

There's a resistor on the aux fan that sometimes goes bad.

Hopefully one of these solves your problem. Unlucky for you, removing the aux fan itself will require removal of the radiator and the condenser, and therefore a drain of the cooling system and an evacuation of the AC system.

I had problems with my aux fan that turned out to be the 25A fuse at position 17. The connector plugging into fuse 17 at the fuse box was partially melted as well. Even after lubing the bearings (this can be done with the fan in place using a McGuiver J-hook from coat-hanger wire and flexible spray straw), the original aux fan was just getting old and drawing about 26 amps. I solved the problem by replacing the fuse with a 30A thermo-resetting breaker wired directly to the battery and now it's running great. I had a long drive to TN and the AC was pumping out ice cold air on demand and the temp gauge in range.

I know you're a stickler for original equipment and you may balk at a non-original breaker mounted on the side of your fuse box. In that event, if your number 17 fuse is toasty, maybe you can find a less conspicuous location or you may need to replace the aux fan.

Good luck and stay cool.
(oo=00=oo) Eric
1981 528i Manual
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Mike W.
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Re: Engine Overheating

Post by Mike W. »

You shouldn't really need the aux fan at highway speeds, not that I haven't heard it come on, but with a good cooling system it shouldn't. 528i aux fans will be inaudible at low speed with the engine running, but easily noticeable on high, high is noisy. The fan switches are always suspect, although again the aux shouldn't be needed on the highway. In town A/C performance would be lousy to terrible if the Aux fan isn't working. I would check the fan clutch too, although it too shouldn't come on when on the highway. Is the radiator original? Ever been rodded out? To me it's always suspect, the old copper and brass didn't cool all that well and the plastic/aluminum E28 ones have more tubes too. All this presumes you don't have a cracked head, which starts small in it's effects, actually initially just by modest coolant consumption, like having to top it off once a month or so.

A useful, but less than perfect test of the radiator it to get it hot then shut it off and feel for cool/cold spots which indicates poor flow. Recoring radiators is an option which I've seen good results with, although I suspect it's getting to be something of a lost art these days. At times I've seen all aluminum E12 radiators for reasonable prices, although without too much effort looking, not currently.

Assuming it is the radiator, an E28 one would probably be the best bet. A bit of work to install, it needs to have a somewhat flexible mounting, but not reinventing the wheel. They're available, not expensive, and work better than original.
Mike W.



1980 528i, 3.5 euro, 5 speed conversion
1981 528i, 3.6, Recaros and more. Project
1998 328is, quick and efficient, but not satisfying
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Jcat
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Re: Engine Overheating

Post by Jcat »

Thanks Eric and Mike. Pretty sure I know the answer to this... but 'is there a way I can tell if my radiator is original or not?' Or... is there a way I can tell anything about it that will help me to determine its age? I have 2 3-ring binders of records on this car. I have to believe that it has been replaced by now. Heck... I have about 300K miles on 'er. I am interested in learning more about how to test different aspects of the system. When driving yesterday back from AL, I had the AC turned off completely while on open highway. The temp retreated, but after trying to get the AC to fire back up, it did not, after turning it on again. It just blew hot air AND the car overheated again, so I turned it back off. Can't radiators be tested for throughput without having to remove the dang things? At least I would then know better about whether to dump some flow-max into it. 8)
J Prothero
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Re: Engine Overheating

Post by Mike W. »

Jcat wrote: Mon Jun 07, 2021 1:10 pm Thanks Eric and Mike. Pretty sure I know the answer to this... but 'is there a way I can tell if my radiator is original or not?' Or... is there a way I can tell anything about it that will help me to determine its age?
Maybe, but not really. There might be something to indicate it's not original, but especially if it's been recored, probably not.
I have 2 3-ring binders of records on this car. I have to believe that it has been replaced by now. Heck... I have about 300K miles on 'er.
Yep, probably not original.
I am interested in learning more about how to test different aspects of the system. When driving yesterday back from AL, I had the AC turned off completely while on open highway. The temp retreated, but after trying to get the AC to fire back up, it did not, after turning it on again. It just blew hot air AND the car overheated again, so I turned it back off.
Not doubting you, but that makes no sense.
Can't radiators be tested for throughput without having to remove the dang things?
Not that I'm aware of on the car. But talk to a radiator shop.

One other possibility is a bad ground. Does the gauge ever move when you turn on the blower or the headlights or anything else? If it does, you might be looking at a bad ground, not an overheating problem.
Mike W.



1980 528i, 3.5 euro, 5 speed conversion
1981 528i, 3.6, Recaros and more. Project
1998 328is, quick and efficient, but not satisfying
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Re: Engine Overheating

Post by Jcat »

Not doubting you, but that makes no sense./quote]

Let me take another stab at this comment. While driving on the highway, the a/c lost is cold air, so I shut it off since running the a/c was making the car run excessively hot, particularly when we we found ourselves in a 30 min backup due to an accident. Once we pulled through the accident with the a/c still off, the temp gauge moderated to mid point now that we had air flowing to cool the radiator, so I turned the a/c back on, but it only blew hot air. I got home and let the car cool considerably. I turned the a/c back on and it worked just fine. I tried it again last night and it worked like it should, but we had much cooler temps yesterday and overcast skies, which I believe made that possible. I just found it odd that the system even worked after letting the car cool down. does that make sense to you, Mike? Also, I re-verified the aux fan and it works when I turn the a/c on and he car is idling.
J Prothero
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1981 528i stock
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canada karl
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Re: Engine Overheating

Post by canada karl »

300K miles?... has the cylinder head ever been replaced?
1976 530i. BMW 59 Triumph TR3A(rolling resto). 67 Triumph TR4A(salvageable). 86 900S Winter car
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Re: Engine Overheating

Post by Jcat »

It was completely rebuilt about 50K ago (or less) before BMW NA used the car in 03 for display in Montvale when they pull the shroud of the E60. The old sat next to the new. Only BMW parts have ever been used on the car. (Speakers are Pioneer tho). It burns no oil and has a very tiny oil leak. However, the A'c has been out for 30 years and only last year did I commit to having it rebuilt. The shop here in the ATL area ONLY does a/c work and prides itself on old cars. They recall working on lots of e12's when they were further from extinction.
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Re: Engine Overheating

Post by Jcat »

One other possibility is a bad ground. Does the gauge ever move when you turn on the blower or the headlights or anything else? If it does, you might be looking at a bad ground, not an overheating problem.
[/quote]

I never noticed any such movement on the temp gauge, but will study that next time I drive it. Also, I think I should begin to look for an e28 rad. Do you think alum rather than plastic, I suspect?
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Re: Engine Overheating

Post by Mike W. »

Jcat wrote: Tue Jun 08, 2021 9:52 am Also, I think I should begin to look for an e28 rad. Do you think alum rather than plastic, I suspect?
While the Al/plastic is problematic on the newer cars with crazy high operating temps and 2 bar (30PSI) pressures, on E12s or E28s for that matter they're just fine. All Aluminum is probably longer lasting, but especially if you're buying new you're unlikely to have any problems with the plastic part.
Mike W.



1980 528i, 3.5 euro, 5 speed conversion
1981 528i, 3.6, Recaros and more. Project
1998 328is, quick and efficient, but not satisfying
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Re: Engine Overheating

Post by Jcat »

Thanks Mike. You have a favorite "go to" for this part?
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Re: Engine Overheating

Post by Jcat »

... and are all e28 rad's the same regardless of year?
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Re: Engine Overheating

Post by Mike W. »

Nissans have worked well for me. I think all years of E28 M30s are the same. 528e and M5 did use different ones, but all 533/535 should be the same. A/T, M/T differences of course too.
Mike W.



1980 528i, 3.5 euro, 5 speed conversion
1981 528i, 3.6, Recaros and more. Project
1998 328is, quick and efficient, but not satisfying
2000 528iit, Vacation mobile/wife's grocery getter
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Re: Engine Overheating

Post by Jcat »

I am pulling the rad now. will have it inspected, as I have to believe its plugged up but its not leaking (yet). stay tuned. will now soon. Crazy how hard it was to find a guy that still rods radiators. three guys in business for 20+ years all said nobody does that much anymore with lower cost plastic options which are new. But to rod it and clean it up its only 670 clams, so I say, why not. lets see if he finds it to be plugged up... Canada Karl got me thinking when he reminded me of the mileage and which made me have the rad checked. Head is fine. Thanks guys!!
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1981 528i stock
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Re: Engine Overheating

Post by Jcat »

Well... geeee, whizzz. I wonder if those spades look healthy. Hmmmm. I discovered this just before pulling the rad out and decided to proceed with the pull despite the obvious corrosion at the 99 degree switch. Not sure if the switch is defective or not, but will look further into that when the rad returns from the rad shop where they will first inspect for proper flow before racing into surgery. My gut is that the rad is fine and the culprit is the 99 degree switch. the 91 degree switch seems to be clean of the corrosion and I will test that too just to be certain. (probably just replace both since they are both original and I'm in this deep already; also with the talk about the 82 <as I recall> degree switches, maybe thats a better upgrade on the low end of the fan speed, particularly with the fact that I am in Atlanta.
I will certainly make sure the female to the spade is clean before pasting some dielectric grease on both male and both female terminations. Will be interested to know if the switches work as they should. Stay tuned.... (something deep inside tells me that I will be hunting for a 528e rad, though. I just dont know which of the e28 rads best fit the tight space that is available... thoughts? (this is an '81 US 528i)
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J Prothero
Roswell, GA
Former FF Ambassador to Montvale
1981 528i stock
Jprothero600@gmail.com
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