My buddies E300 is loosing a lot of antifreeze. There is no indication that it is head gasket related. There are no white clouds of smoke out the exhaust. There are no puddles anywhere. Pulled both plastic underbelly pans and found them to be dry. Checked all hoses with the exception of the fuel heater hoses under the rack of ribs (AKA intake manifold).
Will be doing a pressure test of the radiator. (original to the car).

Any suggestions?

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91 300GD SWB with transplanted 87 OM603 turbo motor

Definitely replace the expansion tank cap just to eliminate that as a variable.

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14 E250 Bluetec "Sinclair", Palladium Silver on Black, 153k miles
06 E320 CDI "Rutherford", Black on Tan, 171k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

Have you checks its not leaking out the waterpump area? I am guessing that the carpets etc are dry (which could indicate the heater core).

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UK spec Mercedes W210 E300 Turbodiesel wagon - OM606.962 with 722.6 transmission - rust free!

Brand new water pump installed by MB no leaks anywhere.
It only has 240,000 miles on it. Runs perfect.

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91 300GD SWB with transplanted 87 OM603 turbo motor

When my car started doing this, I hunted for months until I found that the radiator tank on the left side had split on the flat side under the hose inlet where you can't really see.

The plastic would be tight and hold water when it was cold and also when running at normal temps but upon shut down, the increased temperature and pressure would force coolant out of the crack and straight down onto the ground where it quickly evaporated leaving no evidence.

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-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250

Interesting. Thanks
I also understand that the fuel pre heater can go bad allowing coolant into the fuel stream.

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91 300GD SWB with transplanted 87 OM603 turbo motor

Get a pressure tester on it, that will make the leak show up...

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Head is coming off.

Did you check the trans fluid?

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Gone to the dark side

- Jeff

I don't know if he did. I will check.

After the engine was cool by the next morning there was still pressure in the coolant system. We then used my NAPA exhaust in coolant tester and it registered immediately that exhaust gasses were present.
That is why we are on to the head.

My windshield fluid heater leaked into the windshield fluid. Slow loss and streaks windshield when you use the washer.

I also had a leak at the auxiliary pump on the passengers side by the turbo.

Go Blue Jays GO!

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1999 Mercedes E300TD daily driver sold at 238K miles 106K miles were mine, rust worm got it :-(
2006 Mercedes CDI new daily driver! 56,000 miles May 2016 now 85,625 Apr 2018 and Apr 2019 101,000 miles Apr 2020 109,875. March 2024 135,250

This E300 is now experiencing 1/2 gallon loss every 300 miles. No white smoke out the tailpipe.

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91 300GD SWB with transplanted 87 OM603 turbo motor

The millage is probably about right for a deteriorating old aged head gasket. A half gallon coolant loss every 300 miles might show no white smoke either.

Head job done drives great however pressure still present in upper rad hose next morning after cool down. What I discovered:
I opened the coolant reservoir cap and took a sniff. Strong smell of diesel fuel in coolant and some floating on top! This is Clean fresh diesel fuel floating not black oily residue. My diagnosis is that the Fuel Preheater has internally broken allowing fuel into the cooling system.
There is no other place on the engine where the coolant comes in direct proximity of the fuel.
Suggestions? He will be replacing the preheater.
Mark

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91 300GD SWB with transplanted 87 OM603 turbo motor