The replacement 300D 2.5 I bought after my last one was KIA'd (had it from 90K to 330K) seems to have just a bit of an issue. I didn't have it inspected by a mechanic since we were talking only a $2-3K car here and I figured I could do my own inspection. This car came from a fellow board member who seemed to know the car very well. He did all his own oil changes w/ Rotella, had done the pressure wastegate conversion, and was a generally knowledgeable DIY'er for these cars. The test drive went great, car drove great with engine, tranny, A/C, heat, all working as it should. Interior was very nice but the exterior was a little sun faded. Suspension was a little tired, so in my mind, I budgeted $500-$1K for a suspension rebuild of the critical components. As long as the engine was good and didn't need major work, I'd be OK. Oil was good and jet black no signs of coolant, coolant showed no signs of oil, and a look around the head gasket showed no leakage. No discernable smoke of any color even on hard acceleration. Checked blowby and there was NONE. I did not have a hand mirror with me on the inspection to check the very back of the head but figured I was OK, especially since the seller told me there were no fluid leaks at all (even said there were no leaks in the ad).

Well, make an already long story longer, knowing thee cars and what to look for, as soon as I got the car home after purchase, I got my hand mirror to check the back of the head to put my mind at ease, and sho'nuff, there was a pretty decent head gasket leak at the back corner on the passenger's side. Evidence of a long-term coolant leak was present running down the side of the tranny under the corner of the head. In fact, there was an inch-long stalagtite off the bottom of the unplugged block heater!

So, next step was to determine how bad it was. It wasn't hissing or actively leaking, so maybe I was lucky and the leak had stopped or maybe even was repaired at some point. So I closely monitored the coolant level in the expansion tank over the next tank of fuel and looked at the leak every time I had the car stopped, and this is what I've found. The car leaks about a quart, maybe a bit less, of coolant every 500 miles. The back corner of the head is wet with obvious coolant where the gasket should be about an inch along either side of the actual corner of the head. There is NO sign of coolant being burned that I can tell, there is no white smoke, I even had my friend start it up and dog it up and down the freeway for me with me closely following in my "other car" (Honda) and I did not see any smoke at all of any color. The car does not burn oil, or at least none that I could discern after 500 miles of driving. There are no other coolant leaks other than the head gasket. It does run a wee bit hot, though, 100 deg C at a steady 70 mph cruise at ambient temp of 90 deg F. Idles all day long at 90 deg C even with the a/c on and 95+ deg F ambient temps. It does climb to 105-110 after hard acceleration from a stop to 90 mph, though, but comes right back down to 100 after I let off the gas. I think the temps may be high just from a semi-clogged coolant system, though, and not due to the head gasket (I learned all about the weak-ish cooling system on these cars from my 13 years of owning the previous one...everything has to be working right or it'll run hot). I think the head gasket leak is confined to just coolant leaking outside. My indy is doing a leakdown test on it tomorrow, but I anticipate that to come out fine since there is no evidence of the cylinder being compromised: no white or blue smoke, car starts right up, no oil in the coolant or visa versa. Oh, and the cooling system does not hold pressure overnight.

So, here's my question: Can I just drive it like it is and put in coolant when it gets low? I don't really care that it leaks as long as it's not too much to keep up with by adding a bit of coolant every 500 miles or so. Or is this situation likely to result in it blowing catastrophicly at some point like when I'm trying to crest the Rocky Mountains on my way driving this car from Dallas to Boise which I will be doing week after next? Are the 105-110 temps I regularly see likely to accelerate the deterioration of the remaining gasket material? Do these kind of leaks generally tend to worsen quickly once they start? My previous '92 300D had a perfect head gasket right up until 330K, by the way, so I am not well versed in addressing this situation. Upon looking at gsxr's photos of the top of his block, I believe there is a coolant return line at this corner and that's it. No sign of oil leaking here, so maybe the gasket is leaking at just this one point.

My goal with this car is to have a reliable daily beater for low $. I'd rather not pour $2K into pulling and rebuilding the head if I can help it. Adding coolant every so often is ok. But at the same time, I need the car to be reliable and don't want to end up on the side of the road in southern Utah at 2:00 a.m.. Other than the head gasket leak, the car looks like it will make a good daily beater.

Bad photos of the leak:

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1972 280SE 4.5
1984 300SD, 250K
1991 300SE, 89K
1992 300D (330K miles when KIA'd by mother-in-law 8/10/09 - still sitting in my barn)
1994 E320, 109K
1995 E420, 60K
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