My '74 B-GT started pushing coolant out the overflow almost every time I take it out for a run - not a lot, maybe an ounce or so. Happens about 30 seconds or so after shutting down. And it happens even when the level of coolant is only about 3/8-inch over the tops of the tubes - also, with a new radiator cap or the old one, and a new thermostat. Compression in # 3 cylinder is down a little (less than 10 psi difference from others), but no change in the engine oil, no sign of coolant on the rockers, to indicate a blown head gasket. Even bought an infra-red thermometer, but there's no sign of overheating. Other than pushing out coolant, the engine runs fine and sounds good. I know the '65 Sprite I had years ago didn't do this, so there's something up - just need to find out what. Hoping for something other than combustion gasses getting into cooling system, like keeping it too full - any ideas?
Harry

Have you 'burped' the coolant system?

Harry, Just because the cap is new does not make it a good one. Did this start after you had the new fan installed? Is the car running hotter than before this water push issue started? If i can assist in any way call me. You have my number! Track day with Hap and our MG Italian nite dinner is Nov.14th. Both are fun events. Time to get-er-done. Bob

This started over a month after installing the fan. The bad thing is that the temp gauge went high a couple of times - pretty sure that was both before and after the fan - but no real signs of overheating that I could see.

Tony, 2 things:
1. If heater works, does the system need to be burped?
2. How do I 'burp' the cooling system? Never had this problem in the past.

Bob, thanks for the offer. I'll be in touch this week sometime.

Onward, ever upward!
Harry

Usually upon a coolant flush/change or component replacement (like water pump or heater core) you will have sir in the system. I usually run vehicle at idle with cap removed until it reaches operating temperatire. There are other methods of ensuring that fluid is in all hoses and cavities. Fluid out the overflow means that either the internal psi is too high for teh cap or the cap is engineered too low for the system. Or a just plain worn out radiator neck. At this point I would suggest pulling the radiator and have it tanked and tested. It may have plugged cores and like with cholesterol and plaque build-up as teh volume decreases the pressure increases. Even local parts stores like autozone and napa can test your cap and tell you what its release pressure is. You could add a coolant overflow tank to the overflow pipe, again, available at most local auto stores - easy to install.