Cooling Issues: overheating/wild temperature fluctuations

[zachhke]

I bought an 87 325is a few years back in pretty poor shape. It seems like no one had done any routine maintenance in years. I've slowly been getting it back into shape, and recently I replaced the timing belt and water pump as I had no idea the condition either were in. Before everything was replaced, the car would never overheat and would get up to temperature (a hair below the 1/2 way mark) and stay there. Now the car temperature wildly fluctuates depending on engine speed, swinging from just above the 1/4 way mark on the highway (stays there consistently when cruising at ~65) to starting to overheat in stop and go traffic. There are no more bubbles coming out of the bleeder valve when I open it so I think i've got all the air out of the system.



Do any of y'all have any thoughts on where I went wrong or things I should check? Thanks!

Zach

[mcr_driver]

Have you been checking how much coolant you have lost or none at all, what is the condition of the coolant? Any headgasket work?

[zachhke]

Have you been checking how much coolant you have lost or none at all, what is the condition of the coolant? Any headgasket work?

I'm not losing coolant, the reservoir is full, just shy of the mark from when I topped it off last during bleeding. I haven't done any headgasket work, and although I don't know the history on the car, it was cooling fine before I got in there (for the past ~2 years).

[jlevie]

My first thought would be a bad fan clutch, but a bad thermostat is also a possibility. Both are probably well overdue for replacement.

[603Racing]

Try the thermo first, they're pretty cheap. You may also want to take a tempurature reading manually to make sure that your temp gauge isn't on death's door. Odd that it reads on the cool side and that's what makes me think thermostat.

[zachhke]

My first thought would be a bad fan clutch, but a bad thermostat is also a possibility. Both are probably well overdue for replacement.

Try the thermo first, they're pretty cheap. You may also want to take a tempurature reading manually to make sure that your temp gauge isn't on death's door. Odd that it reads on the cool side and that's what makes me think thermostat.

Thank you both, I'm going to try the thermostat today. It makes sense to me at least that if the thermostat is locked open I'd run cool on the highway and in stop and go traffic I'd overheat as the thermostat wouldn't be allowing time for the coolant to drop temp in the radiator. Hopefully at least...

[jlevie]

A stuck open thermostat will cause the engine to run cold all the time. One that isn't opening all of the way could allow the engine to run hot when idling but not at speed. You can replace the thermostat, but the odds are that the fan clutch is also bad.

[zachhke]

A stuck open thermostat will cause the engine to run cold all the time. One that isn't opening all of the way could allow the engine to run hot when idling but not at speed. You can replace the thermostat, but the odds are that the fan clutch is also bad.

Odds are you were right. I replaced the fan clutch after work today, and all is well. Thank you very much!