87 300 TD coolant issue
 

I'm not sure I'm diagnosing this correctly and would appreciate some help. Last week the dash warning light came on for the radiator - showing low on coolant. Temp was right where it should be. I checked the expansion tank and found it was about 1" - 1.5" low. And I could see signs of wetness around the tank's outside mid-section parting-line and some wetness under the tank on the inner fender wall. I think I can see a hairline crack but not sure. So I "diagnosed" a small crack in the plastic tank. A few days later the dash warning light came back on - and this time the fluid was barely 1/2" low. That seems like too small a loss to trigger the warning light. So my questions are: Is that enough coolant loss to trigger the dash warning? And what else could be triggering the dash warning light? What else should I be doing to get a complete diagnosis? Does this call for pressure? BTW I'm pretty certain I replaced this tank about 50K ago. Peachparts lists a newer part number, and MB is only new purchase option they list. Thanks.

The loss of coolant aside, could be something like the coolant level sensor's magnet/float has lost it's buoyancy and is failing to position its internal magnet close enough to the reed switch resulting in a false low coolant signal.

Both a leak/loss and sensor issue happening coincidentally seems pretty rare. But I can check for that.

The sensor is in the side of the tank. Unless it's defective, then the only thing that can cause it to trigger is low coolant level. I think your diagnosis if a small crack in the header tank is probably on target.

Yeah. I'm tempted to try epoxy in and out.

Just buy a new or good used tank. Avoid the roadside.

^^^ Agreed 100% My SDL had a crack in it that I tried to fix with epoxy. Didn't hold up. After a couple weeks, instead of just dripping it let go altogether. Spend the money and find a good-used or new bottle. You got 30 years out of the original, it doesn't owe you anything.

The problem is you have to get inside to keep the patch from blowing out. Take a look at what the inside actually looks like:

http://www.peachparts.com/shopforum/diesel-discussion/369376-whats-inside-header-tank.html

Thanks for beating down the epoxy plan with experience and insights Diseasal and MxFrank. I'll get new. But I wanted to ask about the G-05. I checked my coolants found a full jug of Zerex G-05 and a partial jug of MB Antifreeze that does not mention G-05 anywhere on the label. Coolant in the car now is probably 4 yrs old. So probably a good time to X-change. I'm pretty sure the current coolant is the more expensive MB. Are you guys recommending the G-05 as the preferred blend or are they "the same ingredients"?

Hey guys, I just called the dealer in the next city north of me to check prices/availability and was told the 124-500-1849 tank was O/S in the US and Germany. :eek: Then I told him my old tank actually had a different "old" number 124-500-1349. He ran it and my VIN and came back with a lower price and next day availability for p/u. Maybe the -1849 number I found online is a typo.

The M-B coolant for your car and the Zerez G-05 are HOAT coolants, and will play well together.