How Do I Know if Coolant Is Getting Into the Cylinder Head?
- Many -- but not all -- cylinder heads have a coolant-crossover port on the front or the back. Check the front and back of your cylinder head for brass freeze plugs, quite possibly with an Allen-head or square-head recess. If you find one, then pull it with the engine off and check the threads to make sure that it's a coolant passage and not an oil gallery. After you've confirmed that it carries water instead of oil, have an assistant briefly crank the engine over and stop if coolant gushes out.
- Generally speaking, an engine's upper radiator hose attaches to either the intake manifold or the cylinder head itself. If you have an inline engine, then coolant physically cannot go through the upper radiator hose without first going through the head.
- On a V-configured engine, pulling the radiator hose will only tell you that coolant is going through one of the heads; whether it goes through both remains a mystery. The only way to know for sure is to pull the intake manifold off and look at the coolant ports. Obviously, the engine won't start with the intake off, and the water pump isn't likely to pump enough coolant under starter speed to fill the heads. In this case, the solution is to block off the rear head coolant port with a rag and some duct tape, and use a garden hose to pump water into the front port. If there's coolant flow between the head and block, the block will fill up and pour water out of the coolant ports in the other head.
- There is a way to test for coolant flow without pulling anything off, and it involves using a digital thermal contact probe. With engine completely warmed up and running, loosen the valve cover bolts enough to take the cover off, but leave the valve cover on so you don't get sprayed with oil. Have an assistant shut the engine off and then yank the valve cover free. Use your digital probe to test the head casting around the exhaust valve spring seats, the intake valve spring seats and at various points around the head. The head should be a fairly even temperature all around; variances of more than 50 to 100 degrees from any one area to another indicate a lack of coolant flow. The exhaust port flanges are typically much hotter than the rest of the head. so don't bother testing there.