87 300 TD coolant issue

[johnscars]

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.

[ThatOne]

Originally Posted by johnscars

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.

[johnscars]

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

[Mxfrank]

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.

[johnscars]

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

[Mxfrank]

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

[Diseasel300]

^^^ 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.

[Mxfrank]

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

[johnscars]

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"?

[johnscars]

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. 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.

[babymog]

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