Short list for overheating troubleshooting

[bigred88]

Can anyone help me out with a short list of things to trouble shoot with an overheating problem? I can drive around just fine if I'm just putting around, but as soon as I start romping on it it overheats. This is on my Spirit, so I'm not really looking for specific engine stuff, just general what would you look at on any engine.

So far:
Coolant level is fine.
Changed the radiator cap.

Next (my thinking):
Thermostat (any way to check this without opening the engine up?)
Radiator flush and new coolant (to be done in association with the thermostat)

And that's as far as my knowledge takes me. I don't know what else to look at, or if there's something else to do before replacing the thermostat.

Thanks for any help you can offer.

 

[Hogback Fabrication]

What kind of fan (electric, mechanical, mechanical with a clutch, etc)?

Is there a fan shroud?

Stock or modified motor?

Stock radiator?

 

[Burbdood 74]

Have you done a tune-up on it recently? A lean air/fuel mix and timing that's too far advanced can cause overheating IIRC.

What's the condition of your hoses and radiator? If I were you, I would flush out the radiator, change the t-stat, maybe buy new hoses if they're even suspected of being bad and go from there.

 

[jonrpick]

Subscribed for later reference...

 

[str8axle55]

I would start with the t-stat, cheap and easy, just get a good one like a Stant or something. Are you losing any coolant? Is this a 258 or a 4 cyl?

 

[bigred88]

It's a 258. Stock motor, 120K miles. Stock radiator. T-stat was replaced about 5 years ago, when the restoration was completed. That was also the last time the radiator was flushed, but it hasn't been driven much. Maybe 5K miles that whole time, with 2K or so in the last 6 months. I was in college and didn't have the car with me.

It's a clutch fan, has a fan shroud (and placement of the fan within the shroud is correct according to advice I heard while building it- the fan sits right on the edge of the shroud- half in, half out).

It has not had a recent tune up, but as said, hasn't been driven much. I'll keep that in mind though, if the t-stat and radiator flush don't fix it. Hoses should be good, were replaced 5 years/5K miles ago (feel good, but I haven't seen inside of them). Radiator also should be good- no gunk in the coolant or anything like that. And no, it is not losing any coolant.

I'm going to go ahead and do the t-stat and radiator flush this weekend, see how that goes and go from there.

 

[NorCal_Chris]

My old motor in my car was finniky about air in coolant lines. Had to be bled right or the air would gather up after some driving and cause it to Overheat. I would check that. Usually at least with small motors it seems every time i hear of Overheat probs it is a BHG. So i would chek for oil/water and water/oil.

 

[Speedo]

Have you checked the fan clutch when its hot? It should be locked up. Is it puking coolant out of the catch bottle before it overheats. Retarded timing will make it pick up some heat. Start it up and let it run the upper hose should get hot after a fairly short time if the thermostat opens. General maintenance items will make things more likely to show up but usually won't be the cause of a sudden onset problem.

My first guess would be a faulty fan clutch, normal driving will push enough air through the radiator to keep things normal, slow driving like trail running will show a bad fan clutch quickly.

Gus

 

[bigred88]

I haven't checked the clutch fan yet. It doesn't puke coolant at all.

The problem is, it's the slow driving where it's fine. When I'm driving fast (well, lots of accelerating and lots of braking, enjoying some of claifornia's nicer hilly roads) is when it overheats. I know I'm putting more load on it then, but not so much that it should overheat.

 

[bigred88]

School me on thermostats

So I understand the basics of the function of a thermostat- stays shut, allows engine to warm up quickly, then opens, allows coolant to run through the radiator, hence keeping the engine cooler.

So what kind of effects do you have with different temp t-stats? If you go with a lower temp, it would open earlier. will this tend to keep the engine at a lower operating temperature, or will it just take longer to heat up? What kind of disadvantage does a lower temp t-stat carry (or a higher temp for that matter)? Do different engines have a set peak performance operating temp, and you just use the t-stat to try and keep it at the right temp?

I went to kragen yesterday, and in their system the right t-stat for my engine is 195 degrees. I need to cross check that with the factory service manual that I have. Since I'm running a completely stock engine (well, slightly modified ignition), should I stick to whatever is recommended, or are there advantages to changing?