88 325is Overheating - kinda?

[bdmarlow]

Hello all,
I have what seems to be a bit different than any other issue I can find.

I have an '88 325is. I purchased this car about 6 months ago and have done no major work to it. A couple days ago I noticed that it was running hot. To date the car has run mid gauge until this incident. I have spent a couple days researching possible issues and talking to the local BMW guru. This evening I did a driving test and here is what I found.

I fired the car up cold and let it idle. The temp would not move much above the blue.
I started to drive and within a few minuted it was right at the bottom of the red. The gauge has not actually gone into the red but seems to like to live just below it.
Going up hill the car ran right at the bottom of the red. Coming back down the hill (several miles long) it seems to stay in about the same spot just below the red. The only way I can seem to get the car to cool a bit is at about 20mph with the heater wide open. Even at that it only comes down about half a notch (Less than 1/8th of the whole gauge).
Since I couldn't get the the car hot at idle I let it idle for a few minutes in the driveway bit it would not come back down.

When I popped the hood here is what I found.

It wasn't low on coolant.
Not gushing anything.
No coolant in the oil.
I opened the purge bolt and coolant came out pretty quick (you could say squirt).
It has never pushed out steam that I know of.
The top hose was hard.
Top Radiator hose hot - bottom hose cold. Not Less warm, cold.
The top of the radiator was hot - the bottom was cold.

My initial feeling is clogged radiator. I've never really seen a problem like this before but before I go tearing into anything and diving into the money pit I thought I would consult the experts.

Any and all input it much appreciated.

 

[Big Daddy]

Sounds like a thermostat stuck in the closed position, no circulation.

 

[Doughnut]

I would suspect a clogged radiator, any crap (brown water, chunks of rust) in the expansion tank? where you running A/C? is the thermo fan working? fan clutch any good? might be the water pump...
Yeah check the T-Stat out, replace him anyway... Dirt cheap where you live to buy. the cooling system on these old e30's isn't to bad in terms of money to fix, thats if you do it yourself though.

 

[bdmarlow]

Thanks for the quick response.

I'm liking the sound of the t-stat. Cheep and easy is my kind of fix (not sure what that says about me). The Expansion tank doesn't look too bad. Looks pretty green. The fan clutch only spins about 1/4 of a turn cold. So it seems good. I was also under the impression that above 30mph that the fan wasn't really doing much anyway. Am I wrong? The AC was not on. Is there some trick to running the A/C that I should know about?

I'll replace the t-stat asap and see where that takes me. Any tips on that swap? I'll let you know how that works out. Again, thanks for the help. Any additional comments are welcome.

 

[echothreezero]

My first instinct when reading your post was the t-stat also.

You can pull it out and test it by lowering it into hot water and checking how much it opens (there is a specific temp and amount of movement but I don't have my manual in frontof me and I'm not that much of a bmw geek to remember).

You can run the car temporarily with no t-stat - it will just take longer to warm up. The thing is, the flow characteristics of that part of the cooling system means that it actually flows better with an open t-stat than no t-stat. If you don't live in particularly cold climes (like me) then you can get away with drilling holes in your faulty t-stat and putting it back as it is warm enough the engine warms up very fast even with the t-stat open from the start. If you do it in cold areas you will end up running the engine cold for alot longer and accelerate wear and increase fuel consumption.

They are so cheap though you would only do this if you are busy and want to drive the car until you can make time to buy a new t-stat.

 

[bdmarlow]

I'll be picking up a t-stat today and swapping it out asap. Another thought that just came it mind is the fact that the heater blows hot. Will the heater blow hot if the t-stat is bad?

 

[echothreezero]

Yep - the thermostat only stops water passing through the radiator - all of the rest of the cooling system still functions as normal.

 

[E30m42cab]

okay, yes, it sounds kinda like a thermostat, but if the top hose is hot, there's gotta be coolant flowing through the thermostat, so if anything, it's only partially stuck closed/open. Fan clutch may be suspect. Change the Thermostat first... or run it without one for a day like Graham said. Not much of a tip, but make sure you get a new rubber gasket with the thermostat, or at least make sure the old one is clean and smooth, and clean the housing well. If this doesn't work, your water pump might be mad at you.

 

[bdmarlow]

Just got a chance to work on this. Started by draining the radiator fluid to find metal aluminum shavings. I would suspect that someone has put stop leak or a similar product in the fluid. I think I will be replacing the radiator (if it leaked in the past, it's not worth flushing) and doing a very through flush of the block. Any have any input? Or any recommendations on how to flush the block?

 

[Doughnut]

I'm not that much of a bmw geek to remember.

Sure you aren't Graham...

Flushing the block is a messy job.
Drain as much of the old coolant as possible and dispose of it properly like a responsible adult...
Pull the t-stat out and put the housing back on negative the t-stat,

Pull bottom radiator hose off the block and point down to the ground, pull the top hose off on the radiator side and shove a garden hose in, hold on to it tight, then get another responsible adult to turn the water on fast then slow over and over to blast the crap out.

Its actually kinda fun [8)]

 

[bdmarlow]

Just wanted to say thanks for all the help. Once I had the rad off I flushed it with a garden hose. Looked good. I removed the t-stat and threw it in some boiling water... Nothing. Threw the new one in the same water, opened up. Replaced the t-stat and put it back together. Fixed.

Once again, thanks a lot.