Where'd the coolant go? 603 engine - PeachParts Mercedes-Benz Forum

bioTD · #1 04-19-2007, 12:10 PM

87 300TD. 603 engine consistently runs ~80C. 85-90C on long climbs over Mt. Hood.

Had coolant flush and fill last summer (about 8,000 miles ago). Had the low coolant light last week, added water to the coolant reservoir. Checked it a few days later and level (cold) had dropped again. I have searched the form for ways to check for cracked head, and don't seem to have the issues listed, ie the car runs fine, radiator hose not under pressure when cold, oil looks clean (changed about 1500 miles ago), no blue smoke.

Where could the coolant have gone?

It appears the overflow from the reservoir drains onto the ground through the passenger fender? I've not seen any liquid on the ground, do I have a clogged drain or something?

justinperkins · #2 04-19-2007, 12:15 PM

It could have gone internally, the most likely places being the engine (bad news) or the transmission (not so bad).

Since the transmission fluid cooler is embedded in the radiator, if a crack occurs in the two lines at the same place then you will start losing fluid from one place to the other. If fluid gets into your transmission and is left unrepaired, you will eventually blow out a seal, dump all your transmission fluid, and need to get your tranny rebuilt. Don't ask how I know this.

Should be relatively easy to determine from looking at the dipstick of both sources.

dkveuro · #3 04-19-2007, 12:29 PM

Quote:

Originally Posted by bioTD

87 300TD. 603 engine .....................
Where could the coolant have gone?

It appears the overflow from the reservoir drains onto the ground through the passenger fender? I've not seen any liquid on the ground, do I have a clogged drain or something?

The heads crack in many places.
Mostly around the exhaust seat into the coolant jacket.
The likely cause or your loss is a crack into the exhaust throat and coolant is being vaporized while motor running.

There's not a difinitive way of being 100% on the diagnosis unless the leak is obvious.

You 'could' run the engine with the exhaust manifold removed and you'd probably see a wet exhaust port or two.

You could pressurize the coolant system to 20 psi with the injectors and exhaust manifold removed and watch for leaks.

If the leak is small and engine runs okay, do an oil analysis to make sure there is no coolant in the engine oil.

If no coolant present in the sample, then run it untill something changes.

.

bioTD · #4 04-19-2007, 12:43 PM

wow thanks for the quick replies on things to check.

Will watch the tranny dipstick.

As far as engine oil analysis, is there a recommended place to have the analysis conducted? what do I ask them to look for, coolant?

vstech · #5 04-19-2007, 12:47 PM

you could also have a bad rad cap. inspect it VERY CAREFULLY, or just replace it. look for tears or cracks in the rubber parts and cracks in the metal parts of the cap. if your cap is bad, you bettter check your head again. no pressure will kill a 60x head fast.
John

NJ300sdl · #6 04-19-2007, 01:08 PM

The coolant could expand out to the overflow tank and not be drawn back upon engine cool down due to a air leak in the hose. Try temp overflow tank to confirm coolant loss.

larry perkins · #7 04-19-2007, 01:23 PM

the 126 body,like 350sdl has a overflow tank mounted inside the pass side fender,the overflow hose is connected,so you could fill that thing up before you see anything come out of the overflow,looks to hold about 2-3 qts.
would be cheap to test the pressure cap or replace.
larry perkins lou ky