Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Coolant loss

I own a 2002 Merc mountaineer w/ 4.6 v8. I loose 1 qt of coolant per week (400 miles). No leaks on garage floor. I have found a few drops of coolant come out when I remove the oil drain plug. I suspect a leaking head gasket. Repair estimate is 2100. Value of the car with 104000 miles is maybe 4000. Now is not a good time to spend 2100 or replace the car. The rest of the vehicle is in very good condition, clean, no damage interior or exterior, new 17 inch tires. I have researched " fixes" such as Blue devil and Thermoseal. Are they legit? Are ther any other options . Please advise. Thanks Sam

An easy fix not likely. That is a significant leak. This a lot of coolant getting into your oil if that’s where a full quart a week is going. If you keep driving like this you risk much more internal damage, bearings, rings, etc.

Get a confirmation from a mechanic on what exactly is going on.

Additives are not likely to fix a leaking head gasket, IF that’s the problem. Don’t guess on this. There are tests that can confirm a leaking head gasket. The coolant can be tested for combustion gasses. The cylinders can be tested for compression and leak-down. Don’t “assume” you have a leaking head gasket. Test and verify before you decide what to do.

If you really do have a leaking head gasket, the only solution is to replace the gasket.

Something does not sound right to me:

“I have found a few drops of coolant come out when I remove the oil drain plug.”

If you have coolant in the oil, I don’t understand how you would see a few drops come out when draining the oil. you would get an emulsion that might separate into two phases over time. If you are losing a quart of coolant per week into the oil, you would see an increase in the oil volume and the oil would look kinda like mayonnaise, but would probably pour and be gray.

That kind of gasket leaks are very unusual in 4.6 L Ford engines. Has this cooling system been pressure tested? Do you have a good sense of smell and do you know what coolant smells like? Does your Mountaineer have an all-nylon composite intake manifold? If so, check the coolant crossover and thermostat/coolant outlet areas for leaks. It can go into the valley and you won’t see it easily. You can easily get lots of seepage from the casting plugs and sometimes they are hard to see. Have you ruled out simple stuff like the water pump and coolant degas tank? How about the heater core and the hoses? Again, pressure test it.

If the head gasket is leaking, many Ford Modular Motor experts would advise you to swap engines or long blocks rather than change the head gasket. That is partly because pulling the heads may require pulling the motor anyway, partly because low mileage 4.6s are plentiful, and partly, see below. You can swap a long block over several years and vehicles, though I think your Mountaineer might be an aluminum block and that might change things. The salvaged aluminum block engines are popular swaps to save a couple of hundred pounds in cars that are being mildly hot-rodded.

Replacement of the head gasket on these engines requires more care than a lot of shops are used to. They need to check head and block with a straight edge that is flat to within 0.0004 inches over 2 feet. With warranty repairs, Ford does not support local machining if the surfaces are not up to specs. Instead, they send out replacement heads and long blocks. Make sure your shop has done a lot of them before you hire them. Lastly, if it is an aluminum block, check the price of a Ford reman engine. Their reman transmissions are reasonably priced and have an excellent warranty. I have never checked the engine prices.