Heating and cooling

MADDY UZUMAKKI

MEMBER
2000 MERCURY COUGAR
2.5L
V6
2WD
AUTOMATIC
112,000 MILES

I recently bought the car from a friend. He told me the car overheated and he changed the thermostat and still overheated. So he took it out I was expecting not to get heat but I do it actually comes out worryingly hot but my temperature gauge doesn’t ready overheating (recently changed). I was going to start at the water pump, but I look and the reservoir and it steam out into it but only when I hit my gas it doesn’t steam or anything and it only blows hot air when I’m in the 3-8 rpm range. Any suggestions?

1 Reply

STEVE W.

MECHANIC
12,950 POSTS

First off running without a thermostat is a very bad idea as it can cause more damage than repairing the overheating issue. From the description it sounds like you have a couple problems, one being low coolant that has caused an air pocket in the heater core and either a bad pump or a head gasket that is failing. The first thing I would do is top off the coolant to the max mark on the reservoir, start the engine and let it run a couple minutes with the heater on max heat. Now shut it off and check the coolant level on the bottle. Be careful as the coolant tank will be under pressure. Next let it cool down if it warmed up at all, 2 minutes shouldn't be an issue but better safe than sorry. Now start the engine with the cap off and look into the coolant bottle, you are looking for any sign of a steady stream of bubbles or a smell like exhaust in the coolant. One or two small bubbles shouldn't be an issue but if you see a stream like a fish tank bubbler then you have a bad head gasket.

A test that may help confirm that is to pressure test the cooling system.

https://www.2carpros.com/articles/radiator-pressure-test

You can usually get the tester as a loaner tool from a parts store. Follow the instructions for the tool and see if the system holds pressure. A fast cheat on this test would be to install the tester, then see if it pumps up, not release the pressure and set it up to test, but instead start the engine and watch the pressure gauge. What you don't want to see is the pressure rise rapidly when you start the engine. That would be a bad head gasket.

Here are a few other tests if you wanted to be sure:

https://www.2carpros.com/articles/head-gasket-blown-test

A bad water pump wouldn't show those signs as it doesn't create any pressure. It just may not be moving coolant. However with the system that car has you should see coolant flow in the reservoir with the engine running if the pump is working. The "no heat until 3K" sounds like no flow but that could be a bad pump or a plugged radiator. I would start with the gasket testing first. Then if you can rule that out, look at the pump and radiator.