Thread: No more cooling problems

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I'm pretty sure I found the solution that I'm going to share below in these forums, but I can't locate that thread so I'll start a new one to pass this along.

I had a problem with a 400ci small block chevy running the temp gauge to 260 before the thermostat opened. I also found that the radiator was overflowing regularly even after the temp dropped to norma. I'm sure the problem was an air bubble, but didn't want to re-open the system to try to fix it before exhausting all other means. I also didn't want to buy and install an overflow tank if I could avoid it. This is in a hiboy roadster, and I don't like the cleaner looks without the tank.

After trying every suggestion short of opening the system, I finally gave in and pulled the thermostat, then tested it to confirm that it was opening at 185 degrees. While I had the thermostat out, I drilled an 1/8" bypass hole as suggested in the forum I can't now find. I suspect that I purged the air when I removed the thermostat, but I believe that 1/8" hole really helps, too: the engine now warms up smoothly to 185 and holds there. It also doesn't puke coolant any more, so there's no need for an overflow tank.

Dorsey,
What kind of water pump do you have on your small block? I had a similar over heating problem on my SBC 32 roadster and finally traced it to a poor quality "no name" aluminum water pump. Seems that the impeller was installed on the shaft so far away from the body of the pump that it would not circulate adequate coolant in the engine. Took me a long time to figure it out. You can easily check it by removing the pump, and back cover on the pump for inspection.

I now have a flow Cooler high volume pump and seldom even turn the electric fan on even with a "non vented" hood and sides.

Yup, the problem is not just limited to water pumps. As with most parts, you usually get what you pay for. Having had similar problems, I run Stewart Stage 3 pumps, no more cheap pump problems!!!!

I have a chromed stock pump. Two seasons ago, I had the radiator rebuilt and I also installed new hoses due to overheating. In fact, the radiator got so hot that several seams started to leak. For many years prior to that, the engine ran pretty cool, even in traffic on a hot day, and I never did determine what caused the sudden change other than dirt and crud buildup in the radiator.

I have an open engine compartment (see photo) and run a shrouded electric fan. Now that the basic problems are fixed, I can think about a thermostatic fan control so that it doesn't run all the time.

Man, my 350 doesn't make enough heat. It takes 10 minutes to get up to a high enough temperature to open the thermostat. The old engine did it, a new engine does it. It makes it hard to time the choke because it takes so long to warm up.

Originally Posted by 76GMC1500

Man, my 350 doesn't make enough heat. It takes 10 minutes to get up to a high enough temperature to open the thermostat. The old engine did it, a new engine does it. It makes it hard to time the choke because it takes so long to warm up.

Your fix may be as simple as a new thermostat.

Test the old one and the new one in a pan of boiling water.
You can check the opening temperature with a candy thermometer.

Candy thermometers are reasonable in cost and fairly accurate.
They also work well for checking the coolant temp in the radiator so you can see if the car's gauge is indicating correctly.

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As far as drilling holes in the thermostat flange, one is enough.
Two 1/8" holes in the thermostat flange will take about four miles of 35-40 mph driving to get the coolant temp up to 180 or so on a 16 degree F morning (in a roadster).
One 1/8" hole takes about one mile on the same road and speed with the ambient also at 16 degrees.

Been there, done that....

I saw either an ad or an article about drilling three holes, but my reasoning was that to release trapped air one hole would be enough. I'm very happy now that the engine stays cool. When my wife and I first had the car on the road fifteen years ago, I would drive the car when temps were in the 30's and 40's, but those days are long gone, so 16 degrees is purely academic.

Next time I completely drain the system, I'm going to fill the block first through the thermostat hole, then fill the radiator. I didn't do that last time, trusting that the air would release when the thermostat opened. Live and learn.

The holes allow some water to circulate. If there is no circulation, the heads (where the coolant temp sensor is usually located) will get really hot while the intake manifold (where the thermostat senses temperature) stays cool. Drilling the holes lets some water circulate so the engine warms evenly and the thermostat opens before the head temperature gets too high.

In my case, I believe there is too much circulation before the thermostat opens. I have replaced the thermostat and it hasn't fixed the problem, I've even replaced the entire engine. One day, I may study the cooling system of the 350 a little more closely and plug or restrict something so the engine warms more quickly.