1994 SE Overheating Issue

[gk35]

1994 SE. Overheated due to leaking radiator.

Compression test on all cylinders showed 170-180 psi. No coolant found in oil pan. Replaced the radiator and cooling fans, replaced lower and upper manifold gaskets, replaced thermostat. Radiator pressure test at 15 psi showed no leaks.

Problem is right after starting engine the temp rapidly spikes way past 220. Replaced thermostat again. Same issue. Seems as though coolant is not circulating either due to airlock or busted water pump. Is it possible for a water pump to not circulate at all even though no leaks are observed?

[J Wikoff]

It's possible the water pump impeller has broken free from the shaft. Can you take the belt off and spin the pulley by hand and judge how it feels?

[gk35]

It's possible the water pump impeller has broken free from the shaft. Can you take the belt off and spin the pulley by hand and judge how it feels?

Hmm. Will give that a try.

[96 SSEi]

hi, if you start the car from cold with rad cap off, you will see the fluid in the rad neck move about if the pump is working well - the fins rust and then its just an egg beater

also, you can unplug the coolant temp sender that is just below the thermostat housing - this will trigger a fail-safe and force the fans to start on high cool to see if they work well.

[RJolly87]

Did you properly bleed all of the air out of the system? It can really be a pain sometimes getting all of it out.

How long does it take from cold does it take to heat past 220? Do the cooling fans come on?

[gk35]

Did you properly bleed all of the air out of the system? It can really be a pain sometimes getting all of it out.

How long does it take from cold does it take to heat past 220? Do the cooling fans come on?

Not sure I properly bled the system. Will try that. The temp reaches and goes beyond 220 in about 5 min. It does not hover at 220, but instead continues to rise. Fans turn on when over hot. I notice the upper rad hose is cool. Tells me no coolant flow. I took the serpentine belt off to rotate the pump pulley. It turns freely with no resistance.

One other observation. Immediately after starting the engine I see white smoke coming from the front (engine left?) exhaust manifold. I did a cylinder compression test and all are at ~180 psi. Also did a radiator pressure test. Held steady at 15 psi.

So maybe a crapped out water pump, maybe an air lock in the engine block, AND maybe a cracked head gasket?

[RJolly87]

Did the thermostat that you stuck in there have an air bypass area on it? If not, you may need to pull the thermostat to drill a small hole in it to let air through.

I wouldn't be too quick to think major engine damage. These engines can take quite a lot of punishment, and it would likely show up as a coolant pressure leak.

If you could find you something like this, it would greatly help purge air from the system: https://www.amazon.com/Lisle-24610-Spil ... ant+funnel

You should still however be able to at least get it to open the thermostat. I always run the first fill with the radiator cap off, and wait for the coolant to drop when the thermostat opens.

If it still doesn't play nice, even with a thermostat with a bleed provision, I agree with the sentiments of pulling the water pump.

[gk35]

Thanks for the advise RJolly87.

So let me ask this. Instead of drilling a bleeder hole in the t-stat what if I were to remove the t-stat entirely. Then run the engine to hopefully remove any airlock present. Then go back and reinstall the t-stat? Of course I would only remove enough coolant to allow removal of the t-stat housing so as not to introduce any more air.

Would this work?

[J Wikoff]

You'd risk leaving another pocket of air and be right back where you were. Drill the small hole instead.

[RJolly87]

However, you can pull the thermostat to make sure coolant is flowing without it, if any thing to rule out the water pump as a concern.

It's probably easier to drill the thermostat, fill, and then see how it goes from there.

[MKMike]

I use the ACDelco OE thermostats and they have a small hole pre-drilled.
Here's how I fill and bleed the cooling system.

1)Open the bleeder valve.
Fill radiator to base of filler neck.
Wait 2 minutes, then add, as needed.
I also squeeze the upper radiator hose a few times to help purge air out of the bleeder screw.

2)Close the bleeder and install radiator cap with the arrows facing the coolant overflow reservoir tube.

3)Put heater and AC controls in any position except Max and set the temperature at the highest setting.

4)Start engine and allow to idle until the hose from radiator to water pump is hot.

5)Cycle engine speed up to 2500-3000 RPM and back down about 5 times.
Slowly open the bleed valve for approximately 15 seconds to expel any trapped air.

6)Close bleed valve and shut car off.
When cooled to ambient temps, ensure that both the reservoir and the radiator are at proper levels.

If you need to do further testing of the head gasket, this should help
http://troubleshootmyvehicle.com/gm/3.8 ... d-gasket-1

[gk35]

So here is my update. I removed the t-stat and cranked the engine. Right away I noticed coolant flowing across the filler neck. I could also finally feel the upper hose becoming hot. So seems the water pump is functioning.

But... temp gauge still steadily increased past 212. Also noticed a lot of white smoke billowing from the front exhaust manifold as well as from the tail pipe. Although I did a cylinder compression test and a radiator pressure test (both of which indicated no leaks) I think my issue here is a blown head gasket.

[J Wikoff]

A failed lower intake manifold gasket is more likely. It's not as common on pre-95 engines, but it can happen. Blown head gaskets are few and far between on any 3800.

[gk35]

A failed lower intake manifold gasket is more likely. It's not as common on pre-95 engines, but it can happen. Blown head gaskets are few and far between on any 3800.

So I replaced the lower intake manifold a few weeks ago since I clearly noticed coolant leaking up around the junction of the throttle body and upper plenum. Maybe I did'nt torque the bolts down enough? Maybe I didn't seat the gaskets correctly before reassembling?

But lets say the white smoke from the front of the engine is a result of a leaking lower intake manifold gasket. It doesn't help to explain why the engine is still overheating so rapidly. Even when I can detect coolant circulating. Frustrating!

[RJolly87]

How hot did it get when it overheated, and for how long?

Also, was the UIM replaced when you replaced the lower gaskets? Same for the throttle body gasket?

Have you tried bringing it up to temperature with the cap off until the thermostat opens so it's not building pressure? This is typically how I do the first fill after a major drain.

[gk35]

How hot did it get when it overheated, and for how long?



Also, was the UIM replaced when you replaced the lower gaskets? Same for the throttle body gasket?



Have you tried bringing it up to temperature with the cap off until the thermostat opens so it's not building pressure? This is typically how I do the first fill after a major drain.

I turned the engine off before it climbed into the red zone. It would have if I let it.No, but I removed the t-stat and left the rad cap off.
I replaced the UIM plenum, which came with gaskets. I replaces the LIM gaskets but did not replace the lower intake manifold.
Engine still overheated. I saw coolant moving past the filler neck, and also noticed the upper radiator hose was hot.

[96 SSEi]

white smoke with a sweetish smell is coolant burning - I would redo/inspect the lim/uim since heads are very tough on gm cast iron engines.

[gk35]

Well, I decided to change the head gaskets. Good decision! I found out all the water jacket passages in the head gaskets were about 90% clogged. Hence my overheating issues. Valves in head cylinders looked like toast. So I decided to purchase rebuilt head cylinders for $250 each.

Hopefully will have her running in about a week or two.

[J Wikoff]

What do you think caused the clog? Really old coolant or a mixture/wrong kind?