Hello everyone,

My 8 month old 87 300D with 178k on the clock has gone through a lot already since I bought it, but now it seems to have hit the big one: as of about 2 weeks ago, a slow consumption/leak of coolant turned into a major problem. Where I stand now, I'm losing about a gallon of coolant every 25-40 miles of freeway driving. Did all the checks, and this is what I've found:

*Puddles, I found three in the past 3 weeks. Once came from the upper radiator hose where it meets the (6 month old Behr) radiator:



Tightened up the upper radiator hose, but it was already snug. Second and third puddle came from the fender resoirvoir tank, about an ounce once after getting back from a road test with an alignment tech, and for the second time, quite a bit after a couple F/T runs on the freeway (pulling off immidiately after).

*Overnight Pressure: sitting for 8-10 hours, there is still considerable pressure in the system in the morning. Upper hose is pretty stiff, and pressure is released when I open the (brand new) rad cap.

*Smoke: it's very rare, but occasionally I would get a nice healthy cloud of white steam on cold nights during F/T acceleration on the freeway. It was intermittent at best and could not always be done on command. The only moisture I can get out of the tailpipe is some soot-water splatter when the car is idling cold:



*Oil Consumption: negligable. I add maybe a quart of M-1 between oil changes (7500mi).

*External condition of head gasket: there's quite a bit of oil (and possibly coolant/fuel/wiper fluid and whatever else is down there) on the block, all the way around:



*No oil in coolant, no coolant in oil. No bubbles in the coolant as far as I can see.

Problems I've had previously: upper radiator neck broke off during driving, I didn't realize it was broken (thought it just popped off), re-attached the hose. About a week later, the radiator blew up at the neck:



Radiator replaced (Behr).

The car used to get rather hot when going up a hill in warm weather at a "quick pace". On some brutal hills, even babying it with the heater on full blast would have the temp climbing towards 110deg. A/C never used to do much of a difference. Today, the A/C will rapidly push the temp to 100-110deg when idling at a stop. F/T runs will have the temp climbing way too soon.

Pressure in the system when the car is at operating temperature is very very high. The upper radiator hose is hard as styrofoam, and the fender tank gets plenty of overflow. However, even at full pressure/operating temp, the coolant is nothing more than slightly hot.

Since I've added so much additional fluid lately, there is probably only 5% Antifreeze now. This is only as of the last 3-4 weeks -- previously it had "green death" antifreeze in there since the new radiator was installed.

---

At this point, my conclusion is that either my head and/or my head gasket has failed in some way, letting exhaust/pressurized intake air to get into the coolant system. This is over-pressurizing the system, causing the radiator cap to vent steam/fluid to the fender tank, which is overflowing. At one point, this was inadequate to relieve pressure, so the water came out the upper rad hose (pic above). The problem has been present since I bought the car, with the earliest signs being the radiator failing twice in a row (due to excess pressure). Does anyone disagree?

For those of you that do agree it's something about the head/gasket joint, then what ones of you say it's just the gasket, and who says it's the head (Cracked or warped) too?

Now, my question: what can I do until I have the time/parts/money to pull the head and inspect/replace/repair it? I've heard that using coolant leak stop stuff (K&N brand) might help, leaving the radiator cap half open, using a high/low concentration of antifreeze, and all kinds of other crazy stuff to help keep the car going until the surgery. If it is indeed the head, I plan on replacing the it with a 3.5L head, but finding a used one for a reasonable price might take a while -- any advise on what I can do in the mean time would be greatly appreciated.

Any other advice, suggestions, tips, tricks, or anything to help me in yet another major problem for my "problem child" and I'd be much obliged. I've already spent a considerable penny in this car (namely the transmission) so I'd like to be as prepared and knowledgable as possible before I tackle this problem -- but naturally, I want the car to survive until I can take care of it!

Thanks in advance!

Mike
87 Merc 300D/OM603
82 Volvo 240GL/D24