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96 S10 4.3L RWD cooling system pressure problem

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Old 04-23-2011, 05:58 PM   #1
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96 S10 4.3L RWD cooling system pressure problem

Was driving down the freeway, when the engine temp suddenly spiked. I'm pretty sure I was able to get off to the shoulder and shut the engine off before it overheated. I pulled the thermostat, which was stuck shut and replaced it. Now it still slowly overheats and blows coolant out the overflow tank and hose. I f I take off ther radiator cap, coolant will periodically spill out of the cap opening. What could be causing this amount of pressure? water pump? blown gasket?
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Old 04-23-2011, 06:47 PM   #2
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Re: 96 S10 4.3L RWD cooling system pressure problem

did you bleed the air out ....air pockets get stuck and will cause overheating till they are all removed...let it set and warm up w/radiator cap loose when it's not overflowing add more fluid till it stops overflowing and will idle...and "all" S10's are RWD.....not just your's
Old 04-23-2011, 08:27 PM   #3
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Re: 96 S10 4.3L RWD cooling system pressure problem

yes, we attempted to bleed the air out by running the truck for over 5 minutes with the cap off and refilling. everytime we'd fill, it would suck the coolant in, then overflow back out. The coolant is pretty dirty, mostly from a lot of problems i had with the dexcool coolant, but I switched to green when I replaced the radiator a couple years ago.
Old 05-12-2011, 12:09 AM   #4
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Re: 96 S10 4.3L cooling system pressure problem

quick update.

I flushed the radiator and block, did my best to get rid of any air bubbles, then let it idle and it still started to overheat. I noticed some light smoke when idling which got thicker when i revved the engine. Got a couple of other opinions and they all concurred it was a blown head gasket. Dumped a bottle of Bar's Leak Head Gasket Fix in the radiator, let it idle for 15 minutes per the instructions. It still almost overheated by the time it got to the 15 minute mark. Once I shut the engine off, I could still hear coolant sloshing around in the system. I'm going to idle it again with the radiator cap off once it cools down, but I've got a feeling its still going to blow coolant out the top of the radiator cap and still overheat. If that's the case, what other things can i try/look for?
Old 05-12-2011, 03:10 AM   #5
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Re: 96 S10 4.3L RWD cooling system pressure problem

I idled with the cap off for about 20 minutes. once it warmed up, coolant started to overflow, but not as bad as the first time, it finally sucked the coolant level back into the radiator, then i would refill, to have it overflow again (which is normal, right?). I didn't notice any bubbles in the radiator during the whole process. I do think there was an air bubble, as I dumped in about a gallon and a half, but only collected just over a gallon of overflow. The truck got up to about 210 degrees and hovered there, which i think is a little hot. Going to let it cool down, then take it for a short drive....

opinions?
Old 05-12-2011, 04:35 AM   #6
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Re: 96 S10 4.3L RWD cooling system pressure problem

well, I let it warm up idling, but it still started to overheat. when i shut it down there was a lot of gurgling, especially in the upper radiator hose.....
Old 05-12-2011, 06:00 AM   #7
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Re: 96 S10 4.3L RWD cooling system pressure problem

something is wrong then

cooling system needs 15 psi pressure if not then have a leak or cap is bad


thermostat may be upside down or not opening

both rad hoses need to be hot

if one is cold then therm is upside down or pump is not flowing, or rad hose is collapsing or rad is clogged
Old 05-12-2011, 11:19 PM   #8
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Re: 96 S10 4.3L RWD cooling system pressure problem

both hoses were hot and in good shape. there are no blockages as I flushed both the radiator and the block prior to this. Thermostat is brand new and seated properly.

any ideas?
Old 05-12-2011, 11:43 PM   #9
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Re: 96 S10 4.3L RWD cooling system pressure problem

Pull the stat, and see if it over heats with out it. It definitely shouldn't but if so, we can go from there. even though you flushed it there might be some blockage in one of the tiny ports on the head. You said you put The head gasket fix in it due to a leaking HG, if one of the ports was corroded a little the "Fix" will gum it up the rest of the way.
try the no T-stat and see what happens, if it is still over heating, pick up a intake gasket set, and pull it apart see what the ports look like, take pictures if you can. we can have a better idea as to what your looking at .
Old 05-16-2011, 01:46 AM   #10
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Re: 96 S10 4.3L RWD cooling system pressure problem

pulled the thermostat and let it idle for 20 minutes, temp stayed around 210-220. Tested the thermostat in some boiling water and it opened right up, so its not sticking shut (even though its brand new). replaced that stat and idled for another 30 minutes with the same result (stayed about 210). Going to take it for a test drive later after it cools off. Am I good?
Old 05-16-2011, 05:40 AM   #11
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Re: 96 S10 4.3L RWD cooling system pressure problem

......I'm not good......

it overheated slow and steady during the drive, and I noticed a lot of gurgling after I shut off the engine, especially in the upper rad hose. any new ideas?
Old 05-16-2011, 08:03 PM   #12
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Re: 96 S10 4.3L RWD cooling system pressure problem

I recently bought a 1996 S10 with the 2.2L four cylinder engine. It was running 210 to 220 according to the gauge, which agreed closely with my OBDII scanner readout, which I took to mean the gauge sensor and the engine coolant temp sensor signal provided to the PCM were in close enough to indicate the gauge reading was real.

I was sure this was too high, but the previous owner said it was normal for this truck and it had always run at that temp while he owned it.

I replaced the thermostatic fan clutch and it now reads around 175, even in 90 degree weather with the ac running. The OBDII readout again matches the gauge reading closely.

If your engine has the thermostatic fan clutch, it could be the culprit.
Old 05-17-2011, 12:02 AM   #13
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Re: 96 S10 4.3L RWD cooling system pressure problem

Try having the system pressure tested sounds a lot like a blown head gasket allowing combustion gases into the cooling system .
Old 05-31-2011, 02:21 AM   #14
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Re: 96 S10 4.3L RWD cooling system pressure problem

took me a while to get a hold of a compression testing kit, but did the compression test today. 5 cylinders were at 150 and one was at 170, which my buddy told me was normal and wouldn't indicate a blown head gasket. any other ideas on what to look at or try next?
Old 05-31-2011, 05:31 PM   #15
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Re: 96 S10 4.3L RWD cooling system pressure problem

Quote:
I replaced the thermostatic fan clutch and it now reads around 175, even in 90 degree weather with the ac running. The OBDII readout again matches the gauge reading closely.
Look at the fan clutch...
Old 05-31-2011, 07:09 PM   #16
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Re: 96 S10 4.3L RWD cooling system pressure problem

Quote: Originally Posted by lmleck
Look at the fan clutch...
what should I look for? I was also thinking about having a look at the water pump as well....
Old 05-31-2011, 11:51 PM   #17
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Re: 96 S10 4.3L RWD cooling system pressure problem

Quote: Originally Posted by ashcraft
what should I look for? I was also thinking about having a look at the water pump as well....
I don't know of any way to test the fan clutch. It will not pull enough air when it goes bad, but it will seem to be performing ok when feeling for air movement at idle. But if it's bad, the difference in the amount of air the new one will pull is remarkable.

A replacement fan clutch from O'reilly Auto Parts was $40.00 and took about ten minutes to replace, and the results were immediately apparent.
Old 06-01-2011, 12:33 AM   #18
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Re: 96 S10 4.3L RWD cooling system pressure problem

At fast idle with a hot motor, my cooling fan will cycle on and off when heated from radiator heat.
Usually it will run the fan when you first start it cold, you will hear the "roaring" of the fan for a few minutes until the fluid inside of the fan clutch unit stabilizes and then it will become quiet.
When the motor is hot the cooling fan should be running at approximately the speed of the motor. If it appears to be coasting, the fan clutch could be bad, OR there may be a blockage in front of the radiator that restricts air flow and keeps the heat from reaching the fan clutch easily and could cause the motor over heating.
Old 10-17-2011, 11:17 PM   #19
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Re: 96 S10 4.3L RWD cooling system pressure problem

The combination of symptoms you are explaining point to a bad head gasket or cracked head. Check the oil. Sometimes a head gasket will fail only to the point where the hot (high pressure) combustion gases can push past the gasket into the cooling system (which would also explain the dirtiness of the coolant) but the coolant cannot push past into the cylinder. Once a head gasket gets to this point, it is best to stop driving and have the gasket replaced. Once it fails totally and coolant mixes with the oil, the engine has a good chance of being junk. The bearings get contaminated and scrapped. If your oil still looks good, the motor can be saved without having to pull it and replace the bearings.
Old 10-17-2011, 11:25 PM   #20
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Re: 96 S10 4.3L RWD cooling system pressure problem

If the engine runs cooler at cruising speeds but overheats at an idle or very low speed then I would suspect a fan clutch problem. Overheating at cruise then the HG would be suspect. Even with a bad fan the engine should run a few degrees warmer than the thermostat setting at cruising speed.
Old 11-30-2011, 08:46 PM   #21
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Re: 96 S10 4.3L RWD cooling system pressure problem

quick update, I finally just took it in to the shop down the street in June. turned out to be the impeller in the water pump had sheared off. new water pump and it was back to normal.

Recently though, when i'm idling or just at low speeds, the temp stays hotter than normal (about 210-240) until i get back up to high speed, then the temp drops back down. I suspect the fan clutch as people have mentioned earlier in the thread. what's a good way to test if its going bad?
Old 11-30-2011, 08:50 PM   #22
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Re: 96 S10 4.3L RWD cooling system pressure problem

spin it by hand.....if it spins easy, its bad.......it should not spin a whole turn by hand
Old 11-30-2011, 10:00 PM   #23
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Re: 96 S10 4.3L RWD cooling system pressure problem

check it cold first by spinning it it should spin freely. then check it when its hot it shouldnt spin at all. do both test with the engine off
Old 12-02-2011, 03:13 PM   #24
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Re: 96 S10 4.3L RWD cooling system pressure problem

checked it hot and it still spins. how big of a hassle is it to replace?

also, I see clutches list "w/ AC" and "without AC". what's the difference?
Old 12-02-2011, 04:02 PM   #25
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Re: 96 S10 4.3L RWD cooling system pressure problem

nevermind...parts guy explained it to me.
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