1991 s-10 2.5l overheating (delete if not allowed)

Sorry for the wrong forum, but theres a wealth of knowledge here and Im sure someone here can help me...

My father in laws s-10 started overheating, which resulted in a warped and cracked head. He got a new head and rebuild the top end and still over heats. Hes changed thermostat twice, water pump twice ( 2 brand new back to back, both started leaking through the weepholes), and got the radiator flushed and cleaned. IMO, i think its something clogging the water jackets in block or heater core. Starts up fine, runs fine, but start overheating about 15min after startup. Is there any tips and trick to troubleshoot and verify this?

T.I.A.

How are you verifying the temp? Electric Gauge, temp gun, manual gauge?

You can flush the cooling system with water and cascade powder, drive it let it heat cycle a few times. You can even do it with straight mineral spirits.

i do

95burban said:

How are you verifying the temp? Electric Gauge, temp gun, manual gauge?

You can flush the cooling system with water and cascade powder, drive it let it heat cycle a few times. You can even do it with straight mineral spirits.

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nt have either of those, but I do have a bunch of 99% alcohol left over from my AC flush. Would this work?

I planned to take the thermostat out, and unplugg the return hose from the top of the radiator. Stick a water hose in the top inlet of the radiator and try and flush with freshwater though the entire system and have it exit the top radiator hose. Would this suffice?

Have you tried running it up to temp with no thermostat? Just because a part is new is no guarantee that it is functioning correctly.

take the rad and get it flowed tested

95burban said:

How are you verifying the temp? Electric Gauge, temp gun, manual gauge?

You can flush the cooling system with water and cascade powder, drive it let it heat cycle a few times. You can even do it with straight mineral spirits.

Click to expand...

Holy crap, I don't think I'd want to do that. I mean, I know the engine burns gas, but there isn't a couple gallons of gas in the engine compartment and any one time, either, and the op has already mentioned coolant leaks. Plus, I'd be leery of what it might do to the hoses. Is this an old timer trick done with straight sixes and non-detergent oil? Also dish washer soap is much cheaper.

How's fast does the system build pressure? Maybe the head gasket is leaking?

I'd look close at the radiator. If it got bad enough, a flush may not have done much. I think the thermostat removal suggestion is a good one as a diagnostic test.

but I do have a bunch of 99% alcohol left over from my AC flush. Would this work?

Click to expand...

No that would likely be ineffective. Dish washer soap is not expensive. Just go to the dollar store.

You'll be inspecting for all the "usual" problems--plugged radiator, radiator air fins corroded away from the coolant tubes (which almost no one considers--but is really common where roads get salted in the winter), thermostat, water pump, ignition timing and electronic timing advance, warped/cracked castings/failed head gasket pushing combustion gasses into the cooling system, plugged injector/lean fuel mixture, and on and on and on. And all of that bears checking-out. Two failed water pumps in a row would have me looking at the fan/fan clutch; including trying to figure out if they're somehow out-of-balance.





Buddy of mine owned an S-10 with the pathetic Iron Duke. It was, of course, totally worn-out. Got a complete rebuild, including a replacement cylinder head.

Removed the stock cam, replaced with an "Ultradyne"-brand hot-rod cam, replaced the stock rocker arms with Big Block Chevy rocker arms. Ran phenomenal. Except...

Every time he took the truck out-of-town, it overheated. No amount of thermostat changing, coolant flushes, new radiator changed the overheating. Popped at least two head gaskets that I know of.

To shorten-up the story somewhat, it turns out that when he sourced the replacement cylinder head, he matched the original head's casting number to the replacement head's casting number. Same number. Bolted right on, as you'd expect.

Problem was, GM used the same CASTING number to machine (at least) two totally different and NOT interchangeable PART numbers. One part number had a coolant hole drilled "here", the other part number had the cooling hole drilled "there". So when you'd install the wrong part number head onto the head gasket...the cooling passage was mostly but not totally blocked. Had just barely enough coolant flow for low-speed, around-town use; overheated and failed the head gasket at higher rpm/heavier load.

I think he re-drilled the "wrong" part-number head to align with the coolant holes in the block and gasket.

The Iron Duke had HUNDREDS of changes made to it over the course of it's production life, and it's not easy to keep track of what's compatible and what isn't.

95burban said:

How are you verifying the temp? Electric Gauge, temp gun, manual gauge?

Click to expand...

EXCELLENT question.

95burban said:

You can flush the cooling system...

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Does an Iron Duke have block drain(s)? If so, any coolant flush should include draining the block before and after the flush. Drain the coolant and dispose of properly before the flush, drain the flush water and any debris loosened-up by the flush so it doesn't contaminate the fresh coolant.