Mystery Problem

[scottiec]

Alright gang... I am having a very interesting issue and would love to hear some ideas. My car is pushing coolant out of the overflow tank (one that is much bigger than the FF one) after a WOT run. Here are some details:

- The car does not run hot
- When the car cools, coolant in the overflow does NOT get sucked back in to the radiator
- I did a pressure test at 15 llbs and it held pressure
- My radiator cap seems to have a good seal. I can feel the tension when putting it on and I can see the indentation in the rubber seal from the filler neck.
- Dip stick shows no sign of coolant in oil

My two theories:

1. I have an air bubble hiding somewhere.

2. I have a failure in a head gasket that is small enough where it only rears its head during high load situations. The combustion gasses leak into the cooling system which causes too much pressure and it to puke out the overflow. The combustion gasses are higher pressure than the cooling system, no coolant makes it into the cylinder.

Thoughts? Answers?

Much appreciated!

[Garry Bopp]

Scottie,

I had a somewhat similar situation with my coupe (422" Windsor). Whenever I would run it hard, it would suddenly run extremely hot ... combustion air leaking into the cooling system. I would immediately shut down and pull over and use the "lever vent" radiator system to "burp" the cooling system. It would take 30-60 seconds for all the air to bubble out of the system. Small head gasket leak ... no coolant in the oil, just combustion air into the cooling system.

Garry

[Norm B]

The following procedure has worked for me when trying to eliminate air pockets. Try parking the car facing uphill or put the front wheels up on ramps. Remove the sensor or plug in the manifold behind the thermostat. Fill with coolant slowly, shaking the car occasionally, until coolant comes out the port in the manifold. Put the sensor or plug back in and fill the rest of the way. Park the car level and refill the coolant as necessary. Make sure your surge tank is 1/3 full and run the car gently through a couple of full heat cycles. After the engine has cooled, after each heat cycle, check the coolant level and refill as necessary.

If it still blows coolant after that, I would get a coolant tester from your local auto supply store and check your coolant for products of combustion.

HTH

Norm

[joe m]

I also had similar issues. I found the best way to fill the coolant system is with the vacuum fill tool from Snap - On. It works so well I use it on all of my cars because you never have to worry about topping off the system after a couple of heat cycles.

[cwrandolph]

I just went through this yesterday but something that I always do when I fill my system is to crack open the fitting where the temperature gauge bulb goes into the lower intake manifold (see the arrow and the blue fitting in the picture). At somewhere around 2 gallons from empty, I start to see coolant start to seep out of this fitting and I tighten it down. It lets the air out of the top of the engine as the coolant level comes up. Before I started doing this it would take 2 or 3 heat cycles to get it topped off. The other thing that I would check is to verify that your overflow tank has a vented cap - it won't work properly with a sealed tank. Good luck!


82349

[scottiec]

Hi Everyone,

Thank you all for the great advice. I think the next best step is testing for combustion gasses in the coolant.

Scottie

[AC Bill]

- When the car cools, coolant in the overflow does NOT get sucked back in to the radiator.

I could understand why eventually coolant would spew from the overflow tank, if it's not drawn back into the system. It's getting over filled, and has to go somewhere. I would think that you would see a drop in coolant level in the radiator. If you do, and you keep topping it up, the next time it expands, more is pushed into the overflow tank.

I would look at fixing that issue before anything further.
Perhaps the coolant return hose is collapsing under vacuum? Presumably, your overflow tank is venting properly, since coolant escapes from it. Does your rad have the spigot on the cap neck for the overflow hose? Perhaps it is blocked, or the cap seal is extending beyond it, blocking flow?

What psi rad cap are you using? Could the spring be not exerting the correct pressure?

[scottiec]

I could understand why eventually coolant would spew from the overflow tank, if it's not drawn back into the system. It's getting over filled, and has to go somewhere. I would think that you would see a drop in coolant level in the radiator. If you do, and you keep topping it up, the next time it expands, more is pushed into the overflow tank.

I would look at fixing that issue before anything further.
Perhaps the coolant return hose is collapsing under vacuum? Presumably, your overflow tank is venting properly, since coolant escapes from it. Does your rad have the spigot on the cap neck for the overflow hose? Perhaps it is blocked, or the cap seal is extending beyond it, blocking flow?

What psi rad cap are you using? Could the spring be not exerting the correct pressure?

Bill that’s a good thought. I have not been topping it up. However I need to check and see if the cap is blocking the return of coolant.

EDIT. I have a moroso filler neck and a stant cap. I just ordered a moroso cap to see is there are any differences.

[Gordon Levy]

Tell me a little about your engine. Without some more details I would guess that there is a hairline crack in a head gasket or they were installed backwords.

[scottiec]

Tell me a little about your engine. Without some more details I would guess that there is a hairline crack in a head gasket or they were installed backwords.

Gordon,

It’s a 302 pulled from a 2000 Mercury mountaineer. Converted to carb. 48k on it. I never pulled the heads on it.

[johnnybgoode]

Alright gang... I am having a very interesting issue and would love to hear some ideas. My car is pushing coolant out of the overflow tank (one that is much bigger than the FF one) after a WOT run. Here are some details:

- The car does not run hot
- When the car cools, coolant in the overflow does NOT get sucked back in to the radiator
- I did a pressure test at 15 llbs and it held pressure
- My radiator cap seems to have a good seal. I can feel the tension when putting it on and I can see the indentation in the rubber seal from the filler neck.
- Dip stick shows no sign of coolant in oil

My two theories:

1. I have an air bubble hiding somewhere.

2. I have a failure in a head gasket that is small enough where it only rears its head during high load situations. The combustion gasses leak into the cooling system which causes too much pressure and it to puke out the overflow. The combustion gasses are higher pressure than the cooling system, no coolant makes it into the cylinder.

Thoughts? Answers?

Much appreciated!

Any chance the overflow/vent lines are crossed? Scott

[scottiec]

Johnny,
Good thought. Overflow lines are correct and not leaking. Also, I drove the car hard today and after I parked it, my overflow was just about empty. No coolant on the ground, no overheating.

I checked my oil and didn’t see any coolant in it. Could this have been an air bubble? For 650 miles? And no overheating?

[AC Bill]

Perhaps you got the final burp, and the air is gone.

Was the overflow empty on your return, when the car was still hot, or did the car have a chance to cool down?

If it was cooled down, then it sounds like the system was working. I would add some coolant to the OF tank (to the cold line), before driving again, and see what happens the next time your out. You never want all the coolant to be drawn back into the rad, as that may also allow air to enter the system. If your tank is big enough, the next time it gets hot, the tank level will rise, but hopefully not spew coolant.

If the car was still hot, and the OF tank nearly, but not empty, then you've lost a fair measure of coolant at some point, but maybe it's finally at a happy level. I would add more coolant to the tank, and monitor it for awhile.

[scottiec]

Bill,

The OF was very low on my return while the car was still hot. Once it cooled down, it dropped even more (as it should). It was hard to see if it dropped low enough to suck air in. My train of thought is the same as yours. I will add a little, then monitor it.

[Dagwoods]

If you need an excuse to get it up to operating temp, I have a rear axle that needs installing today....a 25 minute drive should be about perfect. Just saying...

[scottiec]

If you need an excuse to get it up to operating temp, I have a rear axle that needs installing today....a 25 minute drive should be about perfect. Just saying...

Hey dude! I would love to but can't swing it today. Let me know though and we can set something up!

[Rootbeer Roadster]

What was your resolution?