I have a 1991 Ford Ranger XLT with a 4.0L. It has 280,000 miles, but I dropped a newer used engine in it a year and a half ago that only has abt. 80,000 miles on it now. It has been running just fine, except for the typical knocking caused by carbon buildup that I recently cleaned out using the Ford "MP3" that worked like a charm.

Anyway... about a month ago, I was running down a small leak in my coolant system. Found the leak : abt. one drop every 10 or 15 seconds, but that added up to abt. a 1/2 gallon every 4 to 5 weeks. The upper rubber return hose was stretched and a little loose where it attached to the pipe coming out of the thermostat. I replaced the hose and clamps, and decided it was a good time to flush my system and add all new antifreeze.

Unfortunately, I bought a Prestone "extended life" antifreeze that I now realize was "recommended" for GM Dex Cool coolant systems. Nowhere on the jug does it say that you shouldn't use this in a Ford or coolant system that was not specifically designed for Dex Cool. In fact it says it can be used in any car or light truck with an aluminum radiator, and specifically lists coolant numbers for Ford and Chrystler, etc. I never read that fine print, but I guess it means it was a mistake to use this in a Ford Ranger with a 4.0L.

The result is, after a month running the Dex Cool antifreeze, I noticed I started loosing a little coolant again, and located a very very slight leak that seemed to be coming from somewhere near the right front area of my valve cover that was not there before (I have been very diligent looking for coolent leaks in the past few months trying to run down the little leak I described above). It was hard to see exactly where it was coming from, as this area is hidded by the alternator and idler pully, etc. Since I was afraid it was an internal gasket, I added some of the high-end Bar's Leaks Liquid Copper, and the leak stopped almost immediately. No more problems for four more days.

But today, my engine started overheating at an alarming rate : I drove three miles from a cold start, and it was pushing the high end of normal and going up. There was obviously pressure in the coolant system, and a lot of coolant had overflowed into and overflowed the reserve tank. So I popped the radiator cap and added water to the running engine for a few minutes until the temps were normal and below. Had to get to work, so I topped off the radiator and drove less than 10 miles, and it was overheating again. Popped the radiator cap again and added water to the running engine until it cooled down to low normal and parked it. There she sits... I am going to flush the whole system with water before I have to drive home tomorrow, and have more water to use if it starts getting hot. But obviously, whatever damage has already been done will need to be repaired--and I'm really worried that repairing the damage might be more work than the truck is worth.

As I read up on the Dex Cool this evening, it seems that there have been serious problems with this coolant eating gaskets ... there were even class-action lawsuits a few years ago! Amazing they keep selling the crap!!! Even more flabberghasted that they don't have a big warning on the jug that says don't use this in any conventional "green antifreeze" coolant system!!! I am especially concerned because I also read that it can damage a plastic intake manifold (which my 4.0L apparently has).

So here's my QUESTION:

What gaskets that come in contact with the coolant might have been damaged?

I would really appreciate if someone could list each gasket and any other parts I need to examine and possibly replace.

Thanks in advance for any advice!

--Nick
in Cottonwood, Arizona

1991 Ford Ranger XLT 4.0L 4x4