Boiling expansion tank

[cleverusername]

Decided to test the Sprint engine and set the electronic fan control, by running it up to temperature. I was adjusting the fan control to come on at 3/4 on the temp gauge. Had to abort because of boiling expansion tank. Before then, every so often I had coolant spurting out, which stopped. I assumed I had overfilled the system.

Then came steam from the tank overflow, so quickly turned off engine and the tank sounded just like a boiling kettle. While getting the car up the temperature, I periodically squeezed the top hoses to make sure they weren't under pressure, which they weren't.

The car has a new pressure cap and a second hand expansion tank. Any ideas?

[Carledo]

Sounds like you got an air lock somewhere.

Don't wish to teach Gandmaw to suck eggs, but you ARE filling it from the stat housing plug aren't you?

Steve

[soe8m]

1. Plastic tanks do stretch so the distance from the seat to the top does become longer and the spring tension of the cap less. Brass tanks don't.
2. New caps are bugger, at least the new ones. The new ones pressure figures arent what they state. If you can buy a NOS one will be better. 18 or 20 PSI ones used on Jags will be fine.

You can test easily with a pressure tester at what pressure the cap opens. It can be that it's way too early.
I alway's make my own caps. Drill out the centre rivet and replace by an m6 bolt and locknut. By adding washers under the spring you can "adjust" the opening pressure. So you can have a cap and tank combi that actually will work.

Jeroen

[cleverusername]

Tested it with new cap, watching the expansion tank, there were bubbles entering while running. So I have ordered a sniff test to check for head gasket failure.

[cleverusername]

1. Plastic tanks do stretch so the distance from the seat to the top does become longer and the spring tension of the cap less. Brass tanks don't.
2. New caps are bugger, at least the new ones. The new ones pressure figures arent what they state. If you can buy a NOS one will be better. 18 or 20 PSI ones used on Jags will be fine.

You can test easily with a pressure tester at what pressure the cap opens. It can be that it's way too early.
I alway's make my own caps. Drill out the centre rivet and replace by an m6 bolt and locknut. By adding washers under the spring you can "adjust" the opening pressure. So you can have a cap and tank combi that actually will work.

Jeroen

Isn't 18-20 psi too high for a Sprint cooling system? I thought it was rated for 13psi?