1989 K5 Blazer: Overheats 2 of 3 times when AC turned on

[SC-Texas]

Here is the problem.

My 1989 Blazer has a digital thermometer. It normally runs are 220f. When the AC is turned on, it normally runs at 232f.

About 2 of 3 times when I turn the AC on, the temp starts to rise immediately and goes over 260f indicated. This occurs when stopped at a light or driving down the freeway.

Does anyone have an idea of what is causing this?

 

[dyeager535]

Bad radiator, pump, coolant fan.

It shouldn't be running at 220*, period. If the t-stat is 195*, it should run VERY close to that at all times.

AC puts more heat into the radiator, if it can't get rid of it, the engine temp climbs.

I'd put money on the radiator though, fan if bad would never stabilize temp, and the pump would be unlikely to be bad enough to JUST let it overheat a bit.

edit: I second the below statement about making sure the radiator fins and area between are clean.

 

[BKinzey]

Probably a thermostat but you are running too hot anyway. Check between the radiator & AC, oil, tranny, whatever coolers you have. Sometimes you can be surprised at the stuff that gets stuck in there.

 

[SC-Texas]

I changed the waterpump a couple of months ago.

I'll check the radiator and various coolers.

 

[4X4HIGH]

I changed the waterpump a couple of months ago.

I'll check the radiator and various coolers.

Did you install the correct water pump? Did this problem start just after installing the water pump? The water pump for that year is a reverse rotation because of the serp belt. The pump physically looks the same as a standard rotation pump but the impeller inside is different.

 

[MaxPF]

That sounds like a classic bad fan clutch. Does the fan turn easily by hand? It should have quite a bit of resistance - it definitely shouldn't freewheel. Fire up the engine, let it idle for a couple seconds, and shut it off while watching the fan. If should stop rotating within a revolution or so. If it spins several revolutions then the clutch is junk.

A clogged radiator will also give you problems. Usually they clog in the middle. Is there sludge in your system or crusty stuff in the tank? This is a red flag.

Check the fan clutch first though

 

[4X4HIGH]

I'm not saying it isn't a fan clutch issue but he said it does this even at freeway speeds. At freeway speeds you don't even need the fan so i doubt that is his issue.

 

[MaxPF]

I'm not saying it isn't a fan clutch issue but he said it does this even at freeway speeds. At freeway speeds you don't even need the fan so i doubt that is his issue.

Missed that part

 

[dyeager535]

Somebody not that long ago alos posted up overheating issues, I believe that was linked to the wrong water pump as well.

A search should find the post, it was fairly descriptive as I recall.