1991 Mercury Cougar Coolant in Oil - Any hope?

DABEL

MEMBER
1991 MERCURY COUGAR
6 CYL
2WD
AUTOMATIC
26,500 MILES

My Cougar overheated. I stopped as soon as I could after light came on, and had it towed home. Haven't started the engine since. (This is it's second engine, with 100,000 on it.) There is antifreeze in the oil. Last time, the thermostat stuck, pistons all knocked into each other and destroyed because it was driven about 12 miles. This time, the rad still has coolant visible, the overflow bottle is riding in between the hot and cold marks. No visible problems with hoses. My main question is: once coolant gets into the oil, is it a lost cause for the engine? I know I need to take to garage for them to see. My dealer is 60 miles away, and I hate to tow it there, only to have them find out that once again the engine is completely gone. Replacing it again is not really worth the 3000 dollars. But if I knew there was a half-way possibility that it might not be ruined, lesser repairs of course, like head gasket and, heater core or whatever it was. I would take the chance and have it towed for a look-see. In your experience, is there a possibility that it wasn't completely destroyed? Or does coolant in the oil usually mean a sad ending?

1 Reply

CARADIODOC

MECHANIC
33,908 POSTS

Hi dabel. Welcome to the forum. About the only thing that will cause this problem is a leaking head gasket but coolant getting into the oil is not the most likely result. On some engines, coolant can leak from a water pump / timing chain cover into the oil pan, but that isn't common either.

The mere fact that coolant got into the oil is not disastrous in itself, at least not right away. The loss of lubrication will lead to piston scuffing on the cylinder walls and real rapid wear of the walls and piston rings. Camshaft journals will wear down too reducing engine performance. None of these things happen right away unless a real lot of coolant dumped into the oil. Once the leak has been diagnosed and repaired, the oil should be changed, and ideally should be changed again a few days or about 100 miles or so, whichever comes first. 95 percent of any coolant will have been drained out during the first oil change, but about five percent of the oil doesn't drain out because it is trapped in various passages. The second oil change will get most of the remaining coolant out.

If a lot of coolant is left in the oil for a long time, it will melt the first layer of metal on the internal bearings. That metal is very soft. Once eaten away, clearances between moving parts will be excessive leading to low oil pressure, and accelerated, continued wear from the hammering action of the pistons and connecting rods.

Don't write the car off yet. Repairs will cost a lot less than monthly payments for a newer one, and in my opinion, you will have a much more reliable car than anything from the last ten years.

Caradiodoc