Expert: Brad Sears - 4/10/2009

Question
QUESTION: I bought an old '66 Plymouth Fury III with a 318 last year and I've slowly been trying to restore it. I'm not a great mechanic, but I try to follow instructions and this thing is super easy to work on.. anyway, I started having an overheating issue last month. I thought it might be the head gasket because I thought coolant was getting into the engine block (the oil looked slightly frothy), but it's not blowing white smoke (or any color smoke at all for that matter) which I understand is a good indication of a cracked cylinder block or blown head gasket? I changed the thermostat today and it's still overheating. I was going to attempt changing the water pump next week but I thought I might ask a professional's advice first. Any help would be appreciated and I'd be happy to follow up on any additional information you'd need.
Thanks!

ANSWER: Ok, the easy check for coolant in the oil is to take the engines dip stick with oil on it as pulled from the engine right after it has been running. Allow the oil to drip on a hot manifold. If the oil dries right up there is no coolant in the oil. If the oil bubbles as it dries there is moisture present. Now a question, when does it over heat, while driving or will it overheat just sitting idling? Let me know as it makes a difference with the diagnosis.
Brad

---------- FOLLOW-UP ----------

QUESTION: I drove it around last night for about 10 minutes and the temperature was sitting near the top end of the gauge, not quite dangerously overheating but definitely more than what'd be considered normal. I drove it around the block twice after that and although it didn't get hotter I decided not to push my luck and parked it.

This morning after letting it idle for a while, I ran some oil from the dipstick onto the manifold and there was no bubbling on the first try. I tried it two more times and both times there was bubbling as the oil dried almost instantly on the manifold.

After idling for 15 minutes, the temp gauge read normal operating temperature as if I'd been driving around before the problem. After 25 minutes idling, she was a little hotter than normal temp. I shut it off after 35 minutes; I figure it would probably eventually overheat, though the temp gauge was climbing much more slowly after the 25 minute mark. Here's the gauge after 15 minutes (here) and after 25 minutes (here). The temp gauge was barely perceptibly higher after 35 minutes than in the 25 minute photo.
Thanks again for the help!
-George

Answer
It sounds to me more like a partially clogged radiator than anything else. If the head gasket was the culprit you would be loosing coolant. The thermostat appears to be working as the temp is up to normal in 15 minutes but the slow rise in temperature indicates a slow circulation especially when driving. Lower the level of the coolant in the radiator by drain some out of the petcock. Look down into the radiator filler neck and see if you can see the tops of the tubes that run down through the radiator. If you can I'll bet that they are partially clogged. If so pull the radiator and take it to your local radiator shop to be boiled out and flow tested. If the radiator is partially plugged that route stands about a 50% chance of fixing the problem. You might have to spring for a radiator.
Brad