The Stovebolt Site Forums The Shop Area Engine Shop Overheating/Spewing coolant

I got my 216 running for the first time today, which is just too awesome , but it has a serious problem. I wanted to break in the cam, so I set the engine running at about 1500 rpm, but after about a minute of running, the coolant level rises and then suddenly gushes like a car in an old movie. I was wondering if maybe it is something with the head gasket, as it was the first I've installed and I didn't get any training, just followed the directions in the manual. Any ideas?

2 questions. 1, is there a thermostat in the engine? Lack of a thermostat will cause too much coolant flow (due to lack of restriction) and will prevent the coolant from dissapating the heat. 2, did you set up a fan or blower to push air through the radiator. While the fan on the engine will move alot of air, it really isn't enough when the engine is run at speed. An ouside source of airflow is needed.

I have a different opinion about your situation. If you are breaking in a cam then of course you need to run it for a certain length of time. The best way to make sure it stays cool would be to run it without the thermostat and work on that later. Also it is difficult to fill the system without leaving some air when the thermostat is in place. Without it you should be able to avoid air. One thing that I do is remove the heater hose that connects just below the thermostat. I then fill the rad until it runs out there, and then replace the hose. If the rad is filled up to the top the expansion will cause coolant to come out when it warms up.

I can't agre with running it without a thermostat. The thermostat acts as a regulator for the coolant flow, and without one, the coolant will flow too fast through the radiator and will not transfer the the heat effectively. There needs to be some sort of restriction in the system to control the flow. At minimum, you sould at least run it with a washer in the housing, I beleive 1/2" ID would do, to restrict the flow (old Flathead trick). As far as filling it goes, there really should be no problems filing it, as the radiator sits higher than the highest part of the engine. The trick is to fill it slow and let the air escape. You should be able to clearly hear it hissing past the thermostat. Then you would want to run it to purge the air, it will do it on it's own as it heats up and the thermostat opens.
If you are concerned about traping air in the engine, you could remove the temp gauge sensor from the back of the head (highest point on the engine) and then fill. But I don't really fell that would be necessary.
I should mention, I work on cooling systems on a regular basis, and have never trapped air in the system. Even on cars with the radiator lower than the highest point in the engine, which is pretty much all late model cars.

I do have the thermostat in place but I had drilled a 1/16" hole in it to allow air to escape. I also had loosened the temp sensor. I ran it again and when coolant started coming out, the top hose and top rad tank were hot but the bottom tank and hose were still really cold, like no circulation is happening.

Another thing to check is the ignition timing. I got a call one time on a 40 Chevy car with the 216 that would get hot within a minute or two of starting and start pushing coolant.

Turns out the timing was quite a bit off, and was firing too far down in the cylinder. Reset the timing and no more heating issues.

If you followed the directions in the manual, then your head gasket is likely okay.

Make sure you leave about 1" of clearance from the coolant level to the radiator cap opening. Since there was no recovery bottle on those old systems, there needed to be some expansion room in the radiator itself. They will belch out excess coolant if over filled.

I have heard arguements both ways about running with and without a thermostat in place.

On the older rigs the radiator is usually quite capable of running without a thermostat, but in my humble opinion I think it better to have one in place. ( And that opinion may not hold water)

The newer vehicles have thinner radiators to save weight, and if the flow is too fast through the radiator then it is inefficient.

Let us know what you find.

How do I set timing? I just made it fire when the needle is over the ball in the flywheel.

I removed the thermostat and the temperature never went over 160. What was the thermostat doing to make it boil over?

Also, now that I let it run for about 20 minutes at something like 1500 rpm, can I let it idle, or do I still have to break in the rings?

You wil be fine letting it idle now that the break in is done. You should change the oil and filter (if equipped) before you run it any further, though.
About the only thing i can think of is that the thermostat is not operating properly, possibly stuck shut. I would not advise running without one when you get it road ready.

Thanks, guys!

There is a good article in Street Rodder for June 09 on cooling systems. It provides a lot of insite into what goes on in the system. There are some interesting comments on the various types of rads too.

What I was basing my guess on is the statement that the truck would push this coolant out after running for just a minute.

Usually a thermostat related problem will take a few minutes for the enigne to warm enough to show up. Though I have seen brand new thermostats bad right out of the box.