Questions and Answers

Mitsubishi Pickup Strange Coolant Loss Q. Hi there Vince, I'm Jun from the Philippines. I own a 2001 Mitsubishi Pickup, 4D56 engine with 41,000 miles. I have a problem with coolant loss. I've changed my head gasket, had the cylinder head resurfaced in a machine shop, new thermostat and radiator cap, secured the clamps and hoses, a newly overhauled radiator which is perfectly leak free and still I lose water coolant at least every three days.

Dry reservoir and 20% coolant lost in the radiator itself. The thing is, that I have not overheated my pick up and the temperature does not rise above mid level even when idle. The last thing I checked was the water pump.

I removed the lower radiator hose where I put a cork to prevent water from coming out, and I also removed the thermostat, and then filled it with water. Obviously water is coming out of the water pump since the hose from our faucet is filling the radiator and the thermostat removed. I started the engine and turned of the faucet.

The funny thing is that the water previously coming out from the water pump stopped too! Isn't it true that upon starting the engine, the water should have burst out since the belts have activated the pump? And if it indeed burst, isn't it a sign of good circulation? But because it stopped flowing, does this mean that replacement of the pump is needed?

Help me please! I should have been buying milk and diapers for my baby than wasting my money on wrong solutions to the real problem.

Thanks a lot...

A. The gist of the problem is that you are losing coolant. At 41,000 miles I would have to say the water pump doesn't have an impeller deteriorated to the point it can't maintain proper flow.

There are only three places where coolant can go, leaking out of the engine, consumed in the combustion chambers and, in rare cases, into the transmission.

When you had the cylinder head resurfaced, did you, specifically, have them check the cylinder heads for cracks? Most machine shops will not take it upon themselves to do that. If you bring it in for a resurface, that's all they will do. I never send a head out without telling the machine shop to check for cracks.

If it wan't checked, a cracked head is a possibility, as is a cracked cylinder block. Since you have a new radiator in the vehicle, we can eliminate the possibility of a leak between the radiator and transmission cooler.

The best, and really, the only way to find out where the coolant is going is to pressure test the cooling system. You will need to get a cooling system pressure tester to do this.

Fill the cooling system completely and remove the spark plugs. Attach the cooling system pressure tester to the radiator filler neck and apply 15 psi of pressure to the cooling system. If the pressure starts dropping right away, you either have the cooling system pressure tester connected incorrectly, or you have a large leak.

A slow drop in pressure indicates a small leak. Sometimes it helps to put a large piece of cardboard under the engine to help isolate the general area of the leak. If there is no external leak, then, with a small flashlight, look inside each cylinder and see if there is coolant inside any of them.

If there is, then you have a cracked head, assuming the head gasket is installed and the head torqued correctly. You may have to maintain the pressure for a couple of hours but the longer you leave it pressurized, the better the chance of finding, exactly, where the leak is.