Getting hot. Unbelievable but true

[zellamay]

Z3M 1998:
I have the fan delete with an added puller fan.
Last summer, in AZ, temp gage would rise slightly at 80 mph.
I could get the gage back to center by slowing to 65 mph, or if AC had been off,
I could cool it by turning on the AC, thus running the aux fan.
I burped it right and made my gills functional (a small gain, but free)
Fixed the problem, all was good.
Then my fan shroud broke, the tank hose rubbed a hole on the engine pulley.
So I removed the shroud and mounted the tank on the radiator.
Now, the gage rises again, only at highway speeds, and ambient is 70 degrees !!
This is crazy.
It never reaches the next line (at about 2 o'clock), but it should rest at 12 o'clock,
once the tstat opens, at current winter temps.
Coolant is about 50-50. Metal water pump and tstat are about 6 months old.
What could the problem be?
I've read many threads on this site on the subject. As I've always said, first suspect is anything
that has been changed recently.
Shroud? Since it only happens at highway speeds, I doubt shroud removal is it.
Water level/air in system. I doubt it. I've checked and burped it twice. No lost coolant.
Tstat? Doubt it. The car warms properly and gage stays at 12 o'clock except at 80 mph.
Water pump not keeping up? Doubt it. It's a decent brand, URO or Meyle, I forgot which.
Some engine problem, like timing? Doubt it. Car runs great.
So .... what ? any thoughts or ideas appreciated.

[khammack]

I WOULD suspect the shroud. The shroud keeps the air in the right place to cool the water in the radiator. Without the shroud, the air is, most likely, not going through the radiator, but around it (to some extent) especially at higher speeds.

[Tom Liberatore]

Sounding a little like a plugged radiator, is it the original?

[jclausen]

Having worked in the automotive field since 1980 and BMW's for a very long time I'm always fascinated why people love to install an electric fan and get rid of the fan clutch when the original coolant system works very well and will need parts replace once in awhile. I know there is a supposed horsepower gain, I'm sure a minor one. I say put your system back to stock. It will work great

[BimmerBreaker]

Having worked in the automotive field since 1980 and BMW's for a very long time I'm always fascinated why people love to install an electric fan and get rid of the fan clutch when the original coolant system works very well and will need parts replace once in awhile. I know there is a supposed horsepower gain, I'm sure a minor one. I say put your system back to stock. It will work great

It's not about gaining horsepower - if the mechanical fan is redundant, and failures of that fan can cause expensive problems (ie. new hood, new cooling system, possibly overheating engine, etc) then why not remove the extraneous mechanical fan? And putting the mechanical fan back on won't necessarily fix the problem... if the car operated fine last year with a mechanical fan delete, no reason it shouldn't do so now - something else changed.

[Curt C]

The shroud helps the mechanical fan pull air through the radiator while at idle or moving slow. At speed there really is no need to pull air because there is sufficient wind speed to push the air through. Some will tell you that a shroud is actually a hindrance at speed because it can block air coming through to a degree. Since your issue is at speed I think the problem is not the shroud. Have you actually measured the temperature? The gauge might just be off a bit. Slightly off to the right of center is probably well within spec.

[deni2s]

At speed there really is no need to pull air because there is sufficient wind speed to push the air through.

Well today I replaced the radiator and now I have high doubts about that, because in front of regular cooler radiator there is transmission oil radiator, in front of that one there is A/C radiator and in front of that one there is aux fan. Wonder what air actually gets to the regular radiator with coolant if there is no puller fan...

[LannVouivre]

Did you verify the fan temp switch wiring? I'm also going to suggest that removing the shroud might be preventing air from properly being directed through the fan. A badly designed or absent shroud was suggested to be bad for cooling in an article I was reading a few years ago, maybe I can find that and present it here...

Also people ditch the clutch fan because not only can it explode and destroy your hood and anything else nearby, but the auxiliary fan is completely adequate alone. The only time I ever had a problem with overheating was when I had air blocking the temperature switch.


https://www.speedwaymotors.com/the-t...omponent/28863
One at random.
Plus, if you spend time diagnosing anything with the engine running while you lean over the bay, the last thing you'd want would be for the fan to blow up in your face. And the clutch fan is in the way of all the pulleys and belts. All that for being unneeded. Maybe you might need it in the M models, but that's mostly due to the front bumper cover being too stylish at the detriment of airflow.

[Curt C]

Have you actually verified the temperature?

A puller fan pales in comparison to a 60 MPH wind. Stick your hand out the window. Now if you have a blockage in front somewhere neither a fan or wind will help.

Yes the shroud is necessary with a mechanical fan. It prevents the fan from pulling air from the sides circumventing the radiator instead of through the radiator. As a result the lack of a fan shroud generally causes an overheat when the vehicle is stationary and not at speed. OP has both a pusher and puller fan so being stationary he should be okay.

[danomite]

If you're having issues of overheating when driving at speed, then your problem is not the fans! The fans provide airflow when the car is stopped or moving slowly...at anything over about 15 MPH, the natural airflow (even at 100F) should keep the car in its operating range (around 95C/195F). You're system is not providing cooled water most likely due to air in the system, a stuck/damaged water pump, or a blockage (most likely in the radiator).

Please don't listen to the nonsense about other things (oil cooler, aux fan, etc) being in front of the radiator...those do not hinder the air enough to cause overheating issues...unless you've placed a solid sheet of something in the front of the radiator!

How old are the radiator and water pump?

P.S. The shroud on the back of the radiator only has an effect for the mechanical fan...it creates a low pressure zone/vacuum, to create airflow across the entire matrix of the radiator. You should certainly make sure that all of the under shrouding is in place and connected properly though.

[RedRedZ]

I have a gauge that sometimes is a tick past 12:00 and sometimes 1:00 with no difference in temperature on my ultragauge. It would be nice to know what the temperature really is.

[rf900rkw]

Sounds familiar. I'm disappointed that the regulars didn't immediately connect this to what I've been talking about in another active thread.

You need to figure out where/why air is bypassing the radiator. Missing plastic, including the kicker under the radiator? MM belly pan? S54 radiator? Airflow through the M bumper is restricted at best, you can't afford to not get work out of every bit.

[zellamay]

Yes, I read that other active thread, and comments here. So far, little new to go on. I doubt the gage is bad because it seems to be accurate at all other times, and repeats itself in varied situations. The radiator is also less than a year old, plus it worked fine through last summer in AZ. I should also say that the gage still responds if I slow down to below 70, and responds to turning on the AC/aux fan (but not as much, because the shroud is gone the fan doesn't pull as well). It's always had the M bumper, from what I read I might try a Z3, but again: it was that way when it worked fine last summer. ..... I'm going to attack a few ways:
First, I'll check out airflow to make sure it's all going through the radiator. The kicker under the radiator needs to be better. It could have opened since last summer.
Second, I'll check for blockage. I hate to take everything apart. ........ Any thoughts on where to look first? ......

[deni2s]

Actually, yesterday I replaced the horror I had in my yellow car's z3 cooling system with new parts in stock configuration, now the cooling system works much better than before, but I still have similar symptoms as OP - after driving for some time at 70mph with around 0C ambient temp, and slowing down to 30mph the needle moves a bit past the center, but never reaches the next line. After some driving or idling it goes back to place. So replaced were all reachable pipes, termostat, radiator, shroud, water pump looked good so that we left there. Aux fan disabled for now (but I think it shouldn't be engaged anyway at that temp). Z3 2.8 bumper, but I am missing undertray panel. And I suspect heater valve might have some issues (still need to check).

[jclausen]

As far as the picture of the dented hood in my long years with BMW I have seen this happen on 2 cars and both were e38 740's, plus your clutch when it's lock up is really loud, like a jet roaring kind of noise, as my customers have described. So yes it can happen but first you would here the loud noise. And on the posting above why is the aux fan not working? If you want to know true tempertures either hook up a real mechanical gauge or use an infrared heat gun.

[deni2s]

And on the posting above why is the aux fan not working?

Electric motor got stuck. Waiting for new one to arrive.

[BimmerBreaker]

Actually, yesterday I replaced the horror I had in my yellow car's z3 cooling system with new parts in stock configuration, now the cooling system works much better than before, but I still have similar symptoms as OP - after driving for some time at 70mph with around 0C ambient temp, and slowing down to 30mph the needle moves a bit past the center, but never reaches the next line. After some driving or idling it goes back to place. So replaced were all reachable pipes, termostat, radiator, shroud, water pump looked good so that we left there. Aux fan disabled for now (but I think it shouldn't be engaged anyway at that temp). Z3 2.8 bumper, but I am missing undertray panel. And I suspect heater valve might have some issues (still need to check).

Without that panel in place, at speed the air will flow under the car, not through the radiator. I'd start with adding the underpanels and go from there, if system works fine in all other operating conditions it may just be as simple as needing the underpanel ducting back in place.

At speed the cooling system in and of itself only really needs to be doing one thing, the water pump needs to be pumping sufficient coolant through the system. That's all. You could have all fans removed and at speed the cooling system should be fine with a functioning water pump. But you also need airflow through the radiator to cool the coolant being pumped through it.
Highway speeds then slowing down means moderate engine load, heat soak and then when you are slowing down the water pump is slowing down too so less flow. This, coupled with poor airflow through the radiator, could cause car to run a little on the hot side in the circumstances you described.

Wasn't it you talking about how people should maintain their 20 year old cars to not worry about cooling system problems... yet you don't have the underpanel in place?

[Curt C]

For those of you worried about the needle moving just to rightof off center go get an infrared heat gun. Better yet go get one of those OBDII plug in senders that link to your phone. You can see exactly what the engine temp is for less them $60 bucks or so. I bet you don’t have a problem. These little cars will run at 220 all day long. Verify the problem before you start replacing $@&T!! But do make sure all panels and plastic is in place.

[BimmerBreaker]

There is also a secret cluster test to read coolant temp. Not 100% accurate but gives an indication whats happening

[deni2s]

Wasn't it you talking about how people should maintain their 20 year old cars to not worry about cooling system problems... yet you don't have the underpanel in place?

I said in the same sentence "or be ready to face the consequences" - that's what I am doing ;P

Yeah, got the yellow car about 2-3 years ago as winter beater (I know - funny choice), but there were bigger problems to solve first than underpanel:
1) rust almost everywhere
2) scratched windscreen - needed replacement
3) one of rear arms was from 4cyl car
4) failing abs sensor
5) vacuum leaks
6) cracked wheel
7) bad thermostat
8) smaller radiator (from 1.9)
9) no fan shroud
10) cracked brake lines
12) leaking roof
13) leaking a-pilar seals
14) seat heaters not working
15) door cards not fitted properly
16) missing trunk lid struts
17) broken side mirrors
18) broken foot rest
19) missing rubber seals for soft top
20) wrong aux fan wiring
21) burned bulbs in instrument cluster and cars interior
22) broken seat belt guide
23) seats shifting
24) no jack or instruments in the trunk
25) no insulation under the hood
26) missing paint plugs in the floor
27) missing jack places
28) missing aerial base
29) oil leak from diff cover
30) failed viscous fan clutch
31) one of radiators fitment points rusted out completely
... millions smaller things

So I feel like I maintained it pretty well, basically by saving that car from being scrapped and at least prolonged it's life. As soon as I will get a chance to get my hands on used underpanel for reasonable price I will buy it. Or better I would like to get underpanel parts from z3m to put them on black car (which has z3m bumper) and put the underpanel parts from black to yellow car.

[deni2s]

Highway speeds then slowing down means moderate engine load, heat soak and then when you are slowing down the water pump is slowing down too so less flow. This, coupled with poor airflow through the radiator, could cause car to run a little on the hot side in the circumstances you described.

Probably something like that, at least I don't feel like that's a big issue at least during winter, and soon aux fan will be in working condition too.

[Blacklane]

As mentioned above briefly, check the temp switch wiring. A number of them have been mis-wired from the factory. Make sure the temp switch is correctly calling for low and high fan speeds for the stock aux fan and that your puller fan is also turning on at the right temperature. There have been a few posts here on the issue.

[zellamay]

It was the thermostat! I finally put a new one in and now the needle stays at 12:00 no matter how I drive the car. While I was checking all the thing suggested, the problem was gradually getting worse. It didn't seem to depend on airflow through the radiator, although turning on the AC(to turn on the electric fans) did make some difference at lower speeds, it was not enough at higher speeds. Also, as the problem got worse it also got irregular: sometimes worse than other times, didn't depend on how I drove. So ... I started thinking: what if the Tstat is opening partially, enough to cool at lower speeds, but not wide enough to cool at higher speeds. So, I removed the "MotoRad" Tstat, (I had put it in new about a year ago), and put in a "Wahler". After all the hoopla, a simple fix. Fair warning to those considering a cheaper Thermostat. ...........(P.S. If you are still considering a cheap thermostat, please see my Classified ad for a used Motorad tstat)

[rasmuw]

It's always good to read a simple and inexpensive resolution at the end of a thread!

[Vintage42]

It was the thermostat! I finally put a new one in and now the needle stays at 12:00 no matter how I drive the car... removed the "MotoRad" Tstat, (I had put it in new about a year ago), and put in a "Wahler". After all the hoopla, a simple fix. Fair warning to those considering a cheaper Thermostat.

When I got my Z3 in 2012 with 30,000 miles, the needle was always at 12:00. But then I put in a ScanGauge and saw the temperature was constantly changing from 170F coasting down long hills to 195F in city stop and go. I assumed that fluctuation was normal.
By 2015 the forum had made me think that was not normal. I put in a new "Original BMW" thermostat from ECST, and the temperature reading became 206F all the time, no matter the driving conditions.