Checking Coolant With Engine Running, No Radiator Cap

The engine is a Chevy 1990 3.1 L with 200,000 + miles on it. I wanted to check the flow of coolant in my radiator, and top it off once the thermostat opened. .I removed the radiator cap from the cold engine, and stated it up, waiting for the thermostat to open.

When the engine was up to temperature, the coolant spurted/splashed out of the radiator filler neck, I've got a feeling this can't be good. Can anyone with some experience in these matters give me some clues?

I can top off the radiator, and after about 60 to 90 minutes of driving, the coolant level is down 1 - 2". Yet there are no external leaks that I can see. Nor has a shop that has pressure tested the system found any problems

Any thoughts on this would be appreciated.

Reply to
KC
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Reply to
Shep

I refilled it by jacking up the front end of the car to get the radiator neck opening up high. Removed the bolt from the thermostat housing, and added coolant to the radiator neck. I never reached a point where coolant came out of the thermostat bleeder opening, though. The radiator neck topped off first and would not take any more coolant.

Is the coolant crossover pipe on the front of the engine, directly behind the radiator filler neck? My manual calls it the throttle body return pipe. I've found the pipe, but not the bleeder.

Reply to
KC

You need coolant coming out of the bleeder or it's still full of air.

I think I would try topping it up in the air, then closing the rad cap and squeeze the top rad hose to see if I can force the air out the bleeder opening.

Could the bleeder be blocked with crud?

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail >
Reply to
Mike Romain

As liquids heat up they expand. Simple as that.

Reply to
Steve

Other vehicles I've checked with the radiator cap off and engine running just had a steady stream of coolant running across the radiator when the thermostat opened, not the spurts and splashes out of the filler neck that this car is doing.

That's why I wondered if the forceful ejection of coolant out of the filler neck was an indicator of something wrong.

Reply to
KC

Ah, sorry I misunderstood, surges of coolant out the neck are a bit differeent than just a steady rise to overflowing.

It can happen under several conditions. If there are air pockets so that spots of metal are getting over-heated and then coolant gets swept onto the patches of hot metal and boils quickly, it can happen. Also if the water pump is absolutely NOT working and the coolant in the block gets progressively hotter until it boils suddenly you can get surges out the cap.

Reply to
Steve

I believe I have air pockets, because of a gurgling sound I hear in the heater core each time the car is started when the engine is cold. I have added coolant to top off the system as best I can, even with the bleeding problems. Then, after about 60 to 90 minutes of driving, the "low coolant" light comes on, and I find that the radiator is about 1 to 2" low on coolant.

I would attribute the drop in coolant to an air bubble breaking free, and being replaced by coolant but with the need to continually add coolant, I'm betting something more serious is at hand. I used to be able to smell coolant after driving the car. A new radiator and radiator hoses eliminated that leak. What's left to check? The water pump whjle the engine is running?

Reply to
KC

The air pockets can make superheated steam or a blast of coolant letting loose when the t-stat opens. A blown head gasket can cause this too. Any tiny bubbles in the coolant or any smoke coming out the rad opening?

One thing you might want to do is pull the spark plugs looking for one that is really clean. If you find one clean one, that would indicate a head gasket leak.

The previous leak could have overheated it enough to blow a head gasket.

Have you done an engine compression test?

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail >
Reply to
Mike Romain

I'll pull the sparkplugs this weekend and take a look. No engine compression test yet. I had it in the shop and asked them to check for leaks. They found a leaky radiator and said that had to be corrected before they could proceed checking with other leaks. I had them replace the radiator, and that seemed to end the external leaks.

But after thinking about it, I should have told the shop that before they replaced the radiator, I needed have the head gasket checked to verify that it wasn't bad. Reason being is that even though the car is in really good shape for a 16 year old car, it has over 200,000 miles on the engine. I'm not sure I would proceed with a head gasket replacement if that turns out to be the problem. I feel the cost might not be worth it on a car with that kind of mileage.

Reply to
KC

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