Fluctuating Engine temp

[crazymikey]

So the 91 I bought the other day runs and drives great. The AC blows ice cold, however the heat is just mild air.

I noticed that if I slowed down through town, the temp would begin to rise from half way (normal), to about 3/4 of the way up the gauge, but never maxing out. Once I got going again, it would settle back down to normal, whether or not I have the climate control shut off, set to cool or max hot.

The electric fan kicks in, and after I shut off the car, the fan runs for atleast 5 minutes before shutting off. The upper rad hose gets boiling hot, while the lower one remains much cooler.

Lastnight I replaced the thermostat and flushed the coolant, including to remember to bleed the t-stat. At first, it seemed like problem solved, but after driving to work this morning and sitting in the drive thru for coffee, the needle began to creep up on me (without climate control on). As soon as I hit the road, it went back down. I pulled into work, parked the car, shut it off, popped the hood and the upper hose was hot again and my fan ran for atleast 5 mins.

The coolant that I emptied from the car lastnight was clean and bright green, looking as if it had been replaced not too long ago. It looked about as clean as the new coolant I replaced it with.

So, I'm stumped. Something is wrong. Blockage? Bad temp sensor? The car's oil was recently changed and is a nice light brown and no signs of burnt smell or coolant in it. ATF is also nice and red and at the full mark with no foul smells.

I don't want to risk driving the car with it running as hot as it gets and do more damage. When you pop the hood, it's very warm under there.

Ideas?

[Noridetoolow]

It sounds like everything is working as it should. Maybe replace the thermostat and see if that fixes it. If not, pull the radiator and have a shop test it, may need to be re-rodded (I think thats the term). Might be working but not as well as it should. Your fan is working so that does not sound like it the problem unless by chance its not spinning as fast as it should but I doubt this, its a simple motor that is either on or off. Hopefully its not your water pump

[crazymikey]

I did the t-stat lastnight. I haven't had any visible signs of leakage of coolant or any coolant smells from anywhere, so I would be almost safe to assume my cooling system is supposedly working as intended...save for the fluctuating temp and the hot temp under the hood.

I've got a spare rad that I can flush and replace it with and see if that does anything.

[Ralphie]

Did you use a OEM t-stat?

I had the original one go on my 93 and i used a cheap autozone replacement and had it fail almost immediately.

Also make sure it's installed correctly...

If all else fails, my money is on a blockage.

[crazymikey]

yeah, since the parts store was closed, I just popped the t-stat out of the '93 SE and put it in to see if it worked, and seems like it's doing a better job than the one that was in it. Though it's probably worth it to just buy a new OEM one anyways. Made sure the O ring was on properly and I installed it with the pin facing up and the spring side going into the engine as it should.

I had the same issue with the 91 SE, it would get warm, but not as hot as this one does. Maybe I'll drain it this weekend and flush the rad and see what happens. The rad thats in the white coupe is pretty gnarly and dirty, so i think I'm better off sticking with the one that's in the car now.

Could there perhaps be a blockage where the upper rad hose goes into the engine?

[Ralphie]

Possibly could be a blockage...

was the other tstat oem or no?

[Noridetoolow]

if you have a blockage chances are its in the radiator. A radiator shop will hook hoses to it at both ends and test the actual flow. If it is not flowing as it should they re-rod it which cleans all the channels and makes it like new again. This is not something you can see by looking at it, it has to be tested. Having them check it is cheap and if it needs re-rodding thats not bad either.

[crazymikey]

Both t-stats looked slightly different, so I don't know which one, if either, were OEM. All I know is that the one I put in is doing a better job than the one that was in it, but everything is now leading me to beleive it is a blockage.

I'm heading out for lunch shortly, so I'll see how it behaves while I'm out picking up lunch.

[Noridetoolow]

Both t-stats looked slightly different, so I don't know which one, if either, were OEM.

If its doing the same thing with the new tstat then it doesnt matter, having a new one from auto parts store fail is kinda a long shot, yeah it can and does happen, might not be as good as OEM but if they failed THAT much they wouldnt sell em. I would not focus on that since you have already swapped it, if the problem persists its most likely something else.

[crazymikey]

So I went out for lunch and had to go downtown to pick up some paint I ordered. The whole 15 or so mins of driving i did, both city and a little highway, the car stayed at normal and when I parked, my fan did not kick on as it never got hot. Had the AC blasting the whole time as well.

[batever]

make sure to recheck your heat again after you get the other thing fixed. It should blow quite hot--and low heat levels there can be because of a blocked heater core or a problem with the valve that controls flow to the heater core.

You're gonna want that heat once winter hits.

[crazymikey]

Ran the car when I got home from work today and checked the levels. The resevois was empty, so I filled it up and toppe dup the radiator. Been driving around all night without a single issue. Not getting hot, fan not running for 5+ mins etc.

Seems like I was just low on coolant after everything had run through and been bled from when I flushed it.

I r dum sumtymz

[dj_ender]

Ran the car when I got home from work today and checked the levels. The resevois was empty, so I filled it up and toppe dup the radiator. Been driving around all night without a single issue. Not getting hot, fan not running for 5+ mins etc.

Seems like I was just low on coolant after everything had run through and been bled from when I flushed it.

I r dum sumtymz

Just a side note, make sure you turn your heater control to hot while you bleed the system to get all the possible bubbles out of it. This allows the coolant or bubbles in the heater core to flush out with the rest of the system.

[crazymikey]

Oooh, good info. Perhaps I'll do that tomorrow just to make sure.

I just drove around in the car and everything was fine, and as I parked it and started walking away, I heard the fan kick on, even though the temp gauge has been reading normal and all the coolant is full.

Engine bay and my front rims are always unusually hot though.

[cloudasc]

The sounds like there is no airflow while at idle, meaning your fans aren't running. When the A/C switch is on both the radiator and condensor fan should be running. I would check to see if maybe you have a bad fan motors by giving each fan direct voltage from the battery. With direct current they should spin. If both motors check out, my next likely guess would the fan thermoswitches. It would explain why you run hot when parked/idle, and normal while moving.