Cooling system mystery

[franks]

My cooling system is over heating. The hose going into the radiator is hot, however the hose leaving the radiator is cold. 45 deg F outside. The gauge is at 3/4 and rising. I replaced the T'stat last night thinking it would help. I also have a bleeding screw leaking which may or may not be relevent. What is going on? See photo.

[632 Regal]

air in the system
the bleeder lets in air when the car is not running and you have to bleed it all out every time you start it now.
dont sound fun at all man.

[Kalevera]

Is the TSTAT correctly installed? I had the same problem on my M30 last month....it was due to the fact that the rubber gasket was in on the wrong side of the tsat -- interestingly, the old one was installed the same way and worked fine. Apparently, my new one needed to have the O ring on the tstat housing side.

oh, ya, like jeff says...bleed that sucka.

best, whit

[632 Regal]

now theres a picture...looks like it correct in that the top big hose is hot. Is it hot where it goes into the radiator too?

[emw525E34]

Hi Franks, I see thats an M20 engine. common problem is : there may NOT be enough coolant in the system. Take off the TOP Hose from Radiation to engine. The Engine inlet part, loosen the clamp and remove that hose. Pour additional coolant mixture until it almost overflows!. Replace the hose and clamp tight. Bleed some more and it should not overheat.

Or else, your Tstat (either not installled correctly or not working: Arrow pointing UPwards on Tstat). Water pump may be a problem.

Common problem is that insufficient coolant in system means steam just heats up the upper part of the hoses while the lower hose are still cool. ie no coolant circulating!!!.

Very common problem for the M20 motor. The top hose fill trick works everytime for me!. Good luck.

[Mr. BILL]

I learned a lot from this board last summer when I had overheating issues. It sounds like you've got air in the system. Especially with a leaking bleeder, which I assume is the one on the t-stat housing. Right?

If it is, then I suggest the following. You're going to have to replace it. When you re-fill the system follow these directions to the letter.

1. If you can, get the front end of the car as high as you can. Ramps would be good.
2. Make sure the heater control is on hot.
3. Drill a small hole in the rim of the t-stat at the top, (arrow).
4. Close the bleeder on the radiator and open the one on the t-stat.
5. Pour in gallon of coolant. BMW is best, Peak is OK too.
6. Pour in distilled water, you'll begin to hear air escaping through the t-stat bleeder.
7. When you "think" all the air is out, evidenced by a continual flow of coolant without bubbles or spitting. Top off the radiator and actually blow into the radiator neck to force coolant thru, eliminating any air left in the system.
8. Close the t-stat bleeder. Snug will do.
9. Open the bleeder on the radiator and fill with distilled water until coolant and no air /bubbles are evident. Then, top off and blow into radiator neck, forcing any air left out. Replace radiator cap.
10. Start engine and when temp comes up, open bleeder screw, allowing air/bubbles to escape. When only a streem of coolant comes out, rev engine to about 2000 RPM's for 15-20 seconds close bleeder.
11. Take car for a spin around the block, open bleeder until no bubbles, then tighten.
12. Repeat 2-3 more times.

That should do it.

Note, I take a wide mouth funnel designed for radiators, line it with a paper towel with a hole in it to blow into the system. You look/feel stupid doing this, but it woks!

Also, be careful not to overtighten either bleeder screw, snug will do.

Good luck.

[franks]

The gasket is between the t'stat and the cover.

[franks]

Yes, but it is real cold leaving the radiator and the temp gauge is on 3/4, ouch.

[franks]

Do rou mean the hose from the t'stat cover to the top of radiator. Or, the hose from the engine, exhast side, to the t'stat cover. I am not sure which hose you are talking about. I was also thinking of the water pump, but it is not leaking or making noise. How can you tell if the flow is correct?

[franks]

It is not the one on the t'stat cover it is the one on the radiator. I belive I have fixed it. The female threads had a small crack and a little special super glue for plastic seems to have fixed it.

[emw525E34]

Front your picture the SECOND "hot" mark is it!. This hose is from TOP of radiator into the top of engine!.

I strongly believe if you have NOT taken that hose off to fill coolant in the engine, total coolant would be less than 60%, this means water pump is not able to pump the coolant as it starts to vaporise. Once you get enough coolant in the system, then you can feel *even* heat in all the hoses flowing in and out of the engine. You can squeeze it to feel the flow. Provided the water pump is ok, that is.

Most independents does not understand this procedure and was impressed when I did it. It takes 30 mins or so to sort out. Unlike hours and kept overheating due to the steam and the radiator reservior seems full , so you cannot fill if you wanted to. I was surprise that it(BMW) was designed this way for the M20 engine.

Best of luck.
PS: remember 50:50 coolant to DISTILLED water mixture.

[emw525E34]

If you take the top hose off to fill in coolant. You DO NOT NEED to touch the bleed screw/nut at the Tstat. Just use the radiator pastic bleeder. This would mean, your system has enough coolant possibly 90% which means your car WILL NOT overheat.

But just to be sure, next day, when you open the radiator cap, you will see that it is close to EMPTY!. The coolant is sucked into the engine when it cools. This also forces the air bubbles out of the Tstat and other crevices. After the third of refilling the Radiator, you will be 100% full as the level will be stable.
Ensure that you have 1 inch of gap between the top level of coolant to the top of the cap if the cap were closed, some air is good. if you fill to the brim, coolant will leak out ofter you drive. Just wasting coolant!.
Good luck.

[Kalevera]

PEAK is okay!?!?


!!!!???!? :0


Alrighty. These systems are self bleeding. Mine did this because the tstat was incorrectly installed and it prevented the tstat from opening all the way and regulating the passages in the tstat housing. I suppose it could be caused by a really messed up radiator as well. The point is that the coolant isn't circulating through the radiator (hence one half of it is hot to the touch and the other is ambient temp/cold and the pipes reflect the same scenario); the water pump is obviously working, and (we hope) the Tstat is as well (did you test it?! I thought my new one HAD to be bad).

I'm still suggesting that the tstat is being prevented from working properly, either because of excessive air in the system (unlikely given that it goes up to 3/4 and stays there - that sucker would ZAP up as the tstat closed due to it sitting in air and not coolant), or it is incorrectly installed (backwards?!).

[franks]

You the man! thanks for the help.

[632 Regal]

but I dont think it should be cold. Its possible that there is a small amount of water going through the thermostat to cause the hose to be hot but not flowing enough. Im going to guess theres a problem with the thermostat and or air in there somewhere.


Yes, but it is real cold leaving the radiator and the temp gauge is on 3/4, ouch.

[homer+vat]

The top hose fill trick works everytime for me!. Good luck.

Thanks emw525E34, i had the same problem. That works a treat now the gauge more or less stays bang on the center position.

Cheers!

[Gene in NC]

If prob persists after fill advice radiator is prob blocked. How many miles? '89 525a has oheated twice from clogged radiator, the first time on Chritmas eve.

[franks]

I replaced the radiator last week. I also change the t'stat to a 71 deg. and it has helped solve most of the problem, not all though.

[genphreak]

I haven't worked on a 525 ever before, but on the water neck of the M30, you can get the two connectors mixed up if you don;t label them. Should one do this, your gauge will monitor the internal temp of the head coolant, not the coolant mix in the thermostat. Is it possible they are mixed up on yours?

How do you know its overheating? Are you hearing it boil inside the head? If you run it without the cap on the overflow tank does it blowing coolant out all over the place to make way for the bubbles of water vapour boiling inside the head?

You probably already checked a thousand times, but could there an air-leak anywhere that could be allowing air into the head/water neck before it pressurises? Of course it would have be enough to stop flow or correct thermostat operation (I doubt it). Mechanics use a machine to pressure test the system and check for leaks with the cooling with the engine cool. Perhaps you can verify 'leak free' status by doing this...

This engine won't self bleed quickly I can imagine. Be careful not to run it for long after it hits half, you don't want to warp the head but you have to KNOW it is overheating... I shut mine down a few times to listen for boiling bubbles once it came onto 1/2 temp in testing it:) GP