M20 Running Cold?

[Schnitzer318is]

Just bought and rescued a 92 325ic that a little old lady let the timing belt go on. Rebuilt a head and put everything back together with new Tbelt, water pump, tensioner, head gasket, and Tstat of course.

Now, she never warms up (runs smooth though). Gauge is constantly at 1/4 mark and if I get on the highway it drops below the 1/4 mark. I was thinking about removing the mechanical fan. Has anyone heard of a NEW Tstat staying open? Those are the only 2 things I can think of.

Thanks in advance for any help.

[jlevie]

That will be either a problem with the thermostat, or a problem with the gage. I realize the the thermostat is new, but even new parts can be bad. And independent check of the engine temperature will tell which is at fault. I use a contact thermometer on the thermostat housing to do this.

Did you use a 75C or 80C thermostat? With a 75C installed the gage won't read much above the 1/4 mark.

[Schnitzer318is]

Crap, I just looked at the empty box. It's actually a 71 degree Tstat. Can I get away with running this and just removing the mechanical fan? Also I am running straight water right now (while checking for leaks after rebuild). If I change to a coolant/water mix, would that help things out? I think I read somewhere that water keeps the engine cooler than mixes.

[Sagaris]

It would be worth replacing it with the correct one. The hotter your engine runs, the more efficient/more powerful it will be but the material the engine is made of cannot handle all of the heat from combustion, hence the reason a cooling system is needed.

A new T-stat can stick open, they are cheap and with anything there can be manufacturing defects. Keep the fan in place unless you want to undo some of the engineering on the car and have yet one more item to worry about (more than you would if it was left in place).


BTW , love the wheels in your sig pic.

[jlevie]

+1

That is too cold a thermostat. It will adversely affect fuel economy and will have a tendency to coke up the head.

Running plain water, or even water plus Water Wetter, will result in corrosion of the cooling system. On a race or pure track car you accept the corrosion in exchange for greater cooling system efficiency and safety (coolant is slippery). But on a street car run coolant for the corrosion protection, if nothing else.

[jlevie]

+1

That is too cold a thermostat. It will adversely affect fuel economy and will have a tendency to coke up the head.

Running plain water, or even water plus Water Wetter, will result in corrosion of the cooling system. On a race or pure track car you accept the corrosion in exchange for greater cooling system efficiency and safety (coolant is slippery). But on a street car run coolant for the corrosion protection, if nothing else.

[Aleman]

Did you use a 75C or 80C thermostat? With a 75C installed the gage won't read much above the 1/4 mark.

Hi R3v,
I'm having the same problem as the OP. Is an 80° recommended, and why do they even make the 71° one I ignorantly bought and installed?

How many miles would you have to run it cold in order to get the 'coking' effect? I've got about 500 miles on since I installed the 71° thermostat. I've got a 4-hour roadtrip planned for the weekend, and it's supposed to be around 2°C outside. My temp gauge sits at about 1/4.
Thanks!

[e30trooper]

The car i just picked up does the same. Runs at 1/4 , if at idle for 15mins it will creep up to the 1/3 mark.

I have a 75° on my 327i and runs about 1/3 at all times. Thats ok for that car because racecar lol

[dnguyen1963]

If I were you, I would change to the correct t-stat and be done.

[mrgraphics]

People usually put lower rated t-stats in to mask other cooling problems, such as a failing fan clutch. Fan clutch . . . $95. 72 degree thermostat . . . $7.

[Aleman]

People usually put lower rated t-stats in to mask other cooling problems, such as a failing fan clutch. Fan clutch . . . $95. 72 degree thermostat . . . $7.

I see... Should I be OK to run the cooler therm in winter for my 4-hour roadtrip? Or should I try to hunt down an 80 degree one at the stealer & swap it out ASAP?

[dnguyen1963]

It should be fine for your road trip, although you will not have much heat for the first 20 min or so. Your gas mileage will suffer, but you will not destroy your engine.

[E30Gus]

I recently replaced my thermostat and now my car runs cool (just over 1/4) and only goes to half way sitting at a light. The old and new thermostats are both 80C. What could cause this? When I install thermostats I drill a very small hole in the top to help bleeding the system and have never had a problem.
Any ideas?

[jlevie]

I recently replaced my thermostat and now my car runs cool (just over 1/4) and only goes to half way sitting at a light. The old and new thermostats are both 80C. What could cause this? When I install thermostats I drill a very small hole in the top to help bleeding the system and have never had a problem.
Any ideas?

That sounds like a partially clogged radiator and/or a bad fan clutch. The temperature should not climb that much while idling.

[Aleman]

If I were you, I would change to the correct t-stat and be done.

I went ahead and paid $54 for an 80-degree thermostat from the stealer and installed it before my trip. The temp gauge was at about 3/8 for the whole trip. That's more like it! :D