DSM Oil Coolers  -  Last updated 02/25/98

Something to think about - These things are over $200 bucks from Mitsubishi, so keep all this in mind next time you replace your filter. If someone else is changing your oil, you are pretty much at the mercy of their knowledge of this system. Most quick lube places probably have no idea of the potential failures. Then again, don't be too alarmed, because this failure seems to rarely come up on the talon digest, so I figure it is few and far between.

Description of DSM oil coolers and summary - 1989 & 1990 turbo DSM models had an air cooled oil cooler which mounted in front of the radiator. It was connected with special hoses and I would consider it very reliable. On 1991 and later turbo cars, an engine coolant to oil heat exchanger type was used.  This oil cooler ran engine coolant and oil through a heat exchanger device to cool the oil. These oil coolers mount to the block and the oil filter screws onto the face of it. It can come loose when you take the oil filter loose. If you tighten the mounting shaft too tight, the pressure can crush the inner radiator like fins of the cooler and cause the oil and water to mix. I learned this the hard way, take my word for it. There is really no faq or answers here, just something to be aware of.

Why I am now on my third oil cooler and how I fixed the problem - My original oil cooler had come loose on the road and dumped all the oil. I quickly shut the car off with no damage and had it towed home. I discovered that the oil cooler had come loose, so I put it back together, extra tight, because I didn't want that thing coming loose again on the road. From that moment on, I had oil in my coolant. I can't remember how I figured this out, but somehow I determined it was the oil cooler that failed, so I bought another one. When I purchased my second unit, I torqued it down also, and it mixed oil and water just like my first unit. I got Mitsubishi to replace it for free as a defective part even though I most likely broke it myself. After I had broken two of them, I decided it was time to cut it open and inspect it closely. It was at this point that I discovered the design flaw that would allow over torquing it to crush it's insides. Before I installed my third unit, I found some perfectly sized washers to stack under the unit. These perfect washers have to be thin enough so that the rubber o-ring will still seal, but thick enough so that the center shaft can take the torque instead of the outer rim.  I haven't had a failure since, and I can tighten the hell out of the shaft with no failures. Unfortuenately, I did not keep the specs on the washers I used, and I have not had any reason to take it apart since. You will just have to find some various washers, and eyeball it to determine how many of what thickness you need. If your stack of washers is too thin, they are just going to float in there and do nothing. If they are too thick, the oil cooler will not sit and you will dump oil all over the ground when the pressure comes up. .. I know, I should have kept the specs on the washers, but at the time, it was an "experiment" and I was loosing faith that anything was going to work.

I wrote all this stuff on the fly, so if you have any ideas or questions, please let me know!

randnet2@earthlink.net

Lets get on with the pictures...

	TOP VIEW - This is a pic of the outside facing of a 1991+ oil cooler. The oil filter screws onto this surface. This is the view you will see if you remove your oil filter. (This unit is already cut in half).
	BOTTOM VIEW - This view shows the end of the package that mounts against the engine. When installed, there should be a rubber o-ring in that groove to seal it. This o-ring is very much like the rubber ring on an oil filter.
	SIDE VIEW - This is the "worth a thousand words" shot. From here, you can see and imagine how this thing works. Coolant flows in and out of the pipes at the top of the pic. Oil flows all through the inner chambers, and the coolant and oil attempts to match temperature. You can see how the center is hollow for the oil filter shaft to go through it. It is hard to see on this pic, but the base of the unit at the point where the shaft goes through it is not as low as the outer rim. Let me attempt to explain. When you install the unit, the rubber seal will squish down and the attaching shaft will apply the torque to the outer rim because the outer rim will hit the mounting surface first. If you keep tightening it, the center section will crush down and eventually bottom out on the mounting surface. At this point, you have probably crushed or distorted all of the inner fins and your oil and water will be mixing. This picture is of a unit that has been crushed and distorted. It doesn't take much distortion to damage the integrity of the tiny inner chambers. Click the picture to see the big version, and if you look close on the bottom surface, you can see a slight curve where the rubber o ring was compressed too tight and bent the unit.

email me at randynet2@earthlink.net