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my 94 s10 with 96k miles, the 4.3 engine overheats WITH the thermostat in….with it out, the truck runs fine but long drives the coolant gets hot and surpasses the middle towards overheating, when the truck turns off, often times it boils out into run off tank. I am installing the tstat correctly and i have replaced the gasket. With the “no spill funnel” i wait and i wait for all the air to come out and after a few minutes of running it begins pouring back into the funnel and i have to quickly shut the truck off because its so hot, this happens within MINUTES of running the cold engine……
On my truck i have changed all hoses, radiator, water pump, tstat, tstat housing, belt. I did a block test for combustion leaks like your video suggested and the fluid did not change color. This is a really frustrating problem as i want to keep this truck but i dont feel its reliable enough for the long drives i enjoy taking. what do you suggest is the problem?
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Perhaps try a lower temp thermostat? Like 180* or thereabouts? You have changed most of the constituent parts of the cooling system save for the heater core which is a real bear to get out on those trucks. Also, have you checked to make sure the clutch for the radiator fan isn’t worn? That could be a problem right there. If the clutch is worn on the rad fan, your truck will get hot eventually, especially in traffic.
i read the clutch on my truck is not supposed to move when cold, i can feel a lot of resistance when i try this. so i think the fan clutch is good……..
Just thinking out loud here..
Have you tried flushing the cooling system?
A partial blockage in the water jacket may be an issue.
Considering the components already replace, you’ve eliminated pretty much every thing else.
Might also look for any air flow blockages (leaves, plastic bags ETC.Depending on the truck’s maintenance history since new, especially if previous owners neglected coolant changes, there could be considerable corrosion on the surfaces of the block’s water jacket and cylinder head coolant passages which might be hampering coolant flow and heat transfer.
A chelating cooling system flush additive, like Gunk’s C124C Super Radiator Flush, might help. If there’s too much corrosion for the flush chemicals to handle, then getting the block and heads “hot tanked” is your only other option. Of course, that involves pulling the engine and disassembling it completely, including crank and cam bearings.
Having said that, let’s hope this isn’t the result of someone having used a “stop leak” product in the past.
EDIT: This page gives one person’s experience with several flush additives and their chemistry. Hope it helps.
[quote=”EliotG” post=173526]If it runs fine with no stat then the stat is either the wrong one (type, temp) or it’s busted.[/quote]
The info is a bit ambiguous, though. He says the truck runs fine without the thermostat, but then says (in the same sentence) that it overheats on long drives. The way it’s written, it’s unclear if that overheat occurs with or without the thermostat installed.
[quote=”Evil-i” post=173528][quote=”EliotG” post=173526]If it runs fine with no stat then the stat is either the wrong one (type, temp) or it’s busted.[/quote]
The info is a bit ambiguous, though. He says the truck runs fine without the thermostat, but then says (in the same sentence) that it overheats on long drives. The way it’s written, it’s unclear if that overheat occurs with or without the thermostat installed.[/quote]
When its out, the truck still over heats on long drives.
When its in, it over heats within minutes, no driving
I would say ive easily put in more than 5 new tstats in this truck thinking they are bad, they are so cheap its not hurting my pocket, but it is pissing me off!!!!!!! I did the “drill a hole in it” also, still same result.
For what you describe, and considering the parts you’ve replaced, I’d be looking at changing the thermostatic clutch for the cooling fan.
To test it, the fan should stop spinning almost as soon as you switch the engine Off. Like within half a second. The test can be inconclusive, though, and sometimes a bum fan can appear to behave normally. Going by feel, checking for resistance to rotation, is a judgement call, and often doesn’t help with diagnosis.
If it was my truck, I’d change the fan clutch at this point, regardless of what the test results are.
Not a whole lot left to test, I’d check the fan the way Evil-i described. The only other thing I can think of is the possibility of clogged passages in the block and/or heads, not sure how one would test for that though.
Do you have any check engine light codes? I’ve heard of engines that are running too lean causing overheating mysteries like this.
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