I am just about at my wit's end!! In restoring my '83 245 Turbo, I put new front seals in the engine, new water pump, new timing belt, and converted to intercooler. Now the water is seeming to boil in the reservoir when I turn the engine off. I thought maybe air was getting into the system someway, but can't see any signs of it. There are no leaks anywhere. The water temperature is good. I have replaced the thermostat and changed the cap on the reservoir. It was another used cap though. I have searched and searched for some possible solution. I understand that a crack in the head or block could cause this, but I see no signs of this. It only started doing this after I put the intercooler in. In doing this, I did have to change the reservoir tanks (from the large boxy one to the smaller round one). Also, what ratio of water and anti-freeze is recommended? I thought maybe that would make a difference since the anti-freeze would raise the boiling temperature. Thanks for any ideas!!

Ok...if it is a blown head gasket, would it only do it when the engine is turned off? It's fine as long as the engine is idling, but if driven a short distance it starts bubbling (boiling) when the engine is turned off. Is there any way to determine for sure if it is a blown head gasket?
Thanks!

Don't assume the worst case! (blown gasket)

If the reservoir cap is bad, there's no pressure being held on the cooling system, which means it will boil at 100C (water at sea level) or about 120C with 50/50 antifreeze. These temperatures are quite likely after shutting off, when coolant stops circulating around exhaust ports and combustion chamber surfaces. Temporary, localized boiling can then occur at those spots, resulting in bubbles in the reservoir. With the engine shut off - no combustion is occurring, therefore no pressure in the cylinders - so I can't see how a gasket leak could cause what you are seeing.

Test your cap and/or replace with a known good one and see what happens.

If you really suspect a head gasket leak, there are test kits at auto parts shops where you can put a bit of chemical in your reservoir and if it turns some color, there are combustion products in the coolant. THEN you have a gasket leak. Or go to a good radiator shop and they will have a sniffer which can detect combustion gasses in there.


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Bob (son's 81-244GL B21F, dtr's 83-244DL B23F, 'my' 94-944 B230FD; plus grocery-getter Dodge minivan, hobbycar MGB, and numerous old motorcycles)

A method I have used is to feed air into the cylinder from either a compression tester fitting or a hollowed out spark plug with an air line fitting brazed to it. The same tool I use for holding valves closed when doing valve seal replacements. When you put air in the cylinder, just watch the header tank for bubbles. When you get to the affected cylinder you will know it!

Don't want to seem like a pessimist -- but are you sure its "boiling" in the reservoir? I can't believe it can be that hot!
The alternative explanation (which you won't like, I'm afraid) is that you've got a blown head gasket and the combustion chamber gases are coming out of the cooling system in the reservoir tank.
Hope it isn't true, though.
Regards,

Install a known good pressure cap.
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Bob (son's 81-244GL B21F, dtr's 83-244DL B23F, 'my' 94-944 B230FD; plus grocery-getter Dodge minivan, hobbycar MGB, and numerous old motorcycles)

I'm not going to speculate on where these bubbles are coming from, but your antifreeze mix should be 50/50
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Drive it like you hate it