Diagnosis help, please

[Barry H]

My '89 GW has always tried to run a bit hot, but has always been managable.

I replaced the water pump recently (it died), and also replaced the lower rad hose.

Now, it generally runs cooler than it did. Short runs do not present a colling issue at all.

But, if I run the AC for a while, or run it up a grade, it will get hotter and hotter. When it's hot, it doesn't seem to cool down, even when the AC is turned off, or driving downhill at freeway speed. When I shut it off, there can be a loud whining or straining sound, then the water will literally start to boil up through the rad cap into the overflow and out. Last time, it happened I looked at the lower rad hose and it didn't look like it was collapsing. Also. the boiling and water coming up into the overflow seemed to stop abruptly with an audible "click", like something switched on or off.

Any of you Wag docs have a diagnosis?

Barry

[solar@clnk.com]

Have you tried removing the thermostat?

[nfroio]

You could install a larger radiator.... never had the prob that you discussed on my Wag, but I had a very. very similar malady on my old '67 Camaro, and I pretty muched solved it by swapping the orig. single core, with a new tri-core rad, and thermostat swap...

Hope that helps.

Noah

[Dan]

I'd agree with Solar. I'd check out the thermostat first before doing much else. It's easy and cheap. If it's stuck partially closed it would restrict the flow. Only after you replace that should you give thoughts about bigger problems.

[Michael]

I would start with the thermostat also. Something tells me to be concerned about the head gaskets. Let me think more and I will explain... :rolleyes:

[Lindel]

Replace the fan clutch, it sounds as if the one you have is on it's last leg.

[Swoop]

I agree that it's probably the fan clutch or the thermostat. I had a similar problem with mine once. Was on a long road trip and the temp gage just kept creeping up slowly. Had to stop several times to let it cool down. When I finally took out the thermostat, it had actually come apart. In other words it was like not having one at all. Taking out a thermostat is the wrong answer. If the coolant just gets pumped through the engine without being regulated by the thermostat, the coolant doesn't spend enough time in the radiator to lose any heat. The result is a gradual increase in temperature (as opposed to a blocked or stuck thermostat, wich will result in a very quick overheat).

[Barry H]

Ah, I do love this forum. Thanks for the quick help guys.

I haven't yet looked at the thermostat, but I figured that would be the quickest and cheapest thing to try. I'll crack it open this weekend.

I only have about 20,000 on a rebuilt engine, so I hope it's not the head gaskets.

I'm considering a new radiator - primarily because the PO said he replaced it before I bought it. Unfortunately, I've found that pretty much everything the PO did was done poorly.

[andy d]

i would replace the thermo 15$, before the fan clutch 70?, and that before the radiator, 150$.

[reddog]

Replace the thermostat like everybody noted but you should also run some flush through before you pull it apart to do the thermostat and pull the lower rad hose and flush the rad backwards with a hose just to be safe. I would also consider replacing the rad cap if it is not recent. Also check the pressure rating of the cap. Should be 13 lbs +.

Kerry