QuestionHi Dick,
I see that you've answered radiator overflow questions before, so I have one of my own. Facts: '68 AMX, 390 4sp., stock engine (except for mod. cam), total timing of 38 deg. or so, engine does not detonate, engine was overhauled 10k miles ago, radiator re-cored with 3-row 3k miles ago, new thermostat (180 deg. according to machinist), new hoses, and amc hi flow water pump, stock fan shroud and fan (not clutch), live in Calif. and use 91 octane fuel with 10% ethanol--no choice about that. Today, while driving around at low speed, temp gauge went in the middle of range, approx. 200-210. Normally, at cruising speed, temp is approx. 165 deg. (changed the temp. sending unit, btw). When I stopped, radiator fluid came out for about a min. I have used 50/50 antifreeze/water; currently, I use "Water Wetter" product and water. Have had similar issues in the past. What do you suggest I do to prevent future occurrences?
Thanks,
Steve
AnswerI'm not sure there is anything wrong with your car. If you do not have an overflow tank on your radiator, with the proper cap for use with an overflow tank, it is quite normal for the cooling system to burp out some coolant after shutdown when the engine is thoroughly warm. If you fill the top tank only to about 2 inches below the level of the radiator cap sealing ring, this will reduce or eliminate the symptom.
Both of my late 60s Imperials (440 engines) do this in hot weather, especially when I run the AC. I live in the high desert, where ambient temps often get into the 3 digits - so I keep the coolant level down about 2 inches from the sealing ring, and generally I have no or very little burping out of coolant after a hard run. In other cars, I have added a coolant recovery tank and changed the cap to the correct style for use with a recovery tank, and that also eliminates the problem. I run a 180 thermostat in both cars, and see about 195 on the temp gauge.
If you do have an overflow tank (AKA recovery tank) and a new, correct cap, and it still burps out water on shutdown, you may have a bad sealing surface in the radiator neck. The way to check for this is to start the engine, then feel the top hose as the engine warms up - after the thermostat opens, you will feel the top hose get hot quickly as the 180 thermostat begins allowing coolant to circulate through the radiator - after about 15 minutes of idling, the top hose should get very stiff - from the pressure being retained in the engine due to proper operation of the cap. If the hose doesn't show evidence of lots of pressure (it should get very hard), the cap is not sealing properly at the radiator neck. Inspect both the cap and the sealing ring to see the problem.
The only thing that bothers me is that you say the engine is only coming up to 165 - if you have a 180 thermostat, the gauge should read around 195 or so when fully warmed up. 165 is too cool for your engine - it will last longer and run better if it runs around 200 or even higher, so long as you have a good pressure cap and recovery tank.
My advice is to go to your local supermarket, in the housewares department, and buy a "candy thermometer" - this looks like a giant fever thermometer - (the type that your Mom stuck where the sun don't shine when you had a fever). These are VERY accurate, and very cheap - you can stick it in the top of your radiator (don't slam the hood on it - it's glass!) and that will tell you EXACTLY what the true temperature is of the coolant that is coming out of your upper radiator hose from the engine. This is close enough to where your temp gauge sender is located that they should agree pretty closely - using this method, you can absolutely determine the accuracy of calibration of your temp gauge.
Other things that are important in high performance engines are the fan shrouding - are you sure that all the factory air deflection panels and the fan shroud are in place and properly shaped and that the rubber flap that prevents air from spilling over the top of the radiator instead of going through the core is in place and in good shape?
One last thing to check is your lower hose - with the engine cool, squeeze the lower hose - if you don't feel the internal spring that prevents it from collapsing, replace the hose with a proper one. Many mechanics are a little weak in physics, and don't understand that the water pump actually pulls a vacuum on the lower hose, especially at road RPM, and this will collapse the hose. These folks see that rusty old spring in there and discard it, not realizing they are causing a problem.
If this doesn't answer your question, post a follow up and I'll try again.
