Possible blown head gasket?

[Admiral]

After a drive the other day, I noticed my '36 sedan spit a bit of coolant out of the overflow tube, which it will do if the radiator is overfilled. I pulled the cap while the engine was running and the coolant was very frothy, which is why some came out. Is this a symptom of a blown head gasket? The car does not overheat nor has it ever boiled over or anything since I restored it. I ran some Thermocure block and radiator cleaner through it last year and replaced the coolant with fresh stuff, so it should be spotless in there. Maybe residual cleaner is what caused the foaminess?

To try and gather some more information, I disconnected the belt so the fan and water pumps weren't spinning and ran the engine up to about 190 degrees F. As it got up to temp, I saw some small bubbles coming up through the driver's side radiator hose (the only one you can see through the radiator cap). They were small in size and quantity but visible. Is this air or steam?

The car uses no coolant, none of it is burning as there's no smoke or stinky exhaust and all the spark plugs look perfect, a nice dusty brown. Do I have to replace the head gaskets?

[flatjack9]

I would flush the coolant again and fill it with straight water. Give it a good run and check the results.

[Talkwrench]

Pull plugs , compression test , watch your vacuum gauge as well..

[hotcoupe]

Compression test, i always do the easiest things first when i'm trouble-shooting.
Tom

[JWL]

Do this----when bubbles show, jab the throttle wide open for 2 seconds. Allow engine to coast down to idle and repeat throttle jab. Do this 3 or 4 times and any leak of combustion gas will become very evident.

[JSeery]

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Compress test, but a leak-down test might be beneficial as well.

[bobH]

John, it's great to have the voice of many years experience... Right-on, and an obvious test when you think of it. Thank you - thank you - thank you.

'Course, there are other tests, too. For example, I've got one of those 'kits' that tests for combustion gas at the radiator cap. And, there is the old idea of getting a smog test guy to sniff at the radiator cap. (I always had trouble with the smog sniffer -- inconclusive results.)

[FlatheadTed]

Often a engine will run rough at the first startup of the day that indicates moisture on a plug ,if so crank it over the next day then pull plugs and look for damp ,

[jayvee34]

IMO, Compression test will tell the tale!!!

[deuce5wndw]

Did you retorque your heads? Were any bolts loose?

[Admiral]

OK, after a busy weekend I finally had a chance to spend a few minutes in the garage to try and diagnose this possible issue.

Per FlatheadTed's suggestion, the first thing I did this evening was crank the engine over for a few seconds with the ignition off to see if any of the plugs were wet with coolant. When I pulled the plugs, they were all bone dry and a nice chocolate-brown color, so that's doubly good.

Next, with the spark plugs out, I ran a compression test. In this department, the engine seems quite healthy. The results are as follows:

1. 115 PSI
2. 115 PSI
3. 115 PSI
4. 120 PSI
5. 118 PSI
6. 120 PSI
7. 111 PSI
8. 127 PSI

After reinstalling the plugs, I got the engine up to about 160 degrees on the thermostat, and I didn't see any bubbles percolating up through the driver's side radiator hose when looking through the top. However, when I held the throttle wide-open a few times for a couple seconds the coolant got very foamy very quickly (thanks for the suggestion, JWL). I wonder if this is just the type of coolant I'm running, an interaction with any residual Thermocure I used last year or some sort of cavitation from the water pumps.

To the point deuce5wndw made about the head nuts, yes, they've all been torqued to about 45 pounds and none were loose.

Since no coolant is coming out the exhaust (or is on the plugs), since the car drives normally and since there was not a trace of antifreeze in the oil, which I changed just two weeks ago, I'm starting to think I don't have a problem after all. At this point, I'll just drive the car and keep an eye on it.

[flatjack9]

If I run anti-freeze in my engine, it does exactly what yours does. Seems like anything over 2500 rpm and I get foaming. Running straight water I have absolutely no problem. My 39 has an open radiator - no pressure cap.

[Admiral]

Originally Posted by flatjack9

If I run anti-freeze in my engine, it does exactly what yours does. Seems like anything over 2500 rpm and I get foaming. Running straight water I have absolutely no problem. My 39 has an open radiator - no pressure cap.

Ah, great to hear! Foaming sounds like normal operation rather than an actual problem. I can sleep better tonight!

[JWL]

I thought you said the waterpumps were not running?? Remove that possible source and repeat the test.

[lotsagas4u]

Prestone antifreeze is bad about foaming in my 33, are you using Prestone by chance?