I have an 87 603A motor in my 90 300GD. Replaced the N/A with the turbo motor Feb of last year. Car runs flawlessly. Temp remains at 80, no oil in the water and no water in the oil.
The Problem is pressure remaining in the system overnight. Hoses are a little firm. I have experienced some sporadic water loss. It only happens occasionally. When it does I see a small puddle under the car. Level drops below the line on the overflow tank.
I have used the Exhaust in coolant tester (see pic) and it tested normal.
In prepping the new engine for install I updated to the new/larger water pump and housing. And sealed the casing bleed hole as recommended.
I have had some dripping from the flushing T and have sorted that out.
I took it to a radiator shop and they said not to worry about it.
I can go weeks without any fluid loss. I have a new Behr pressure cap. There never appears to be coolant coming from the overflow pipe.

Any help would be appreciated.
Mark

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91 300GD SWB with transplanted 87 OM603 turbo motor

I believe that is the classic sign of a cracked cylinder head.
Sorry.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).

But the exhaust gas tester showed no gasses in the overflow tank.

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91 300GD SWB with transplanted 87 OM603 turbo motor

I've had retained pressure occur on various cars, generally is it is a non issue.

Occasional water loss can come from a water pump shaft seal or a corroding hose barb that leaks then corrodes more to seal.

With the engine cold, do a pressure test where you pump air into the cooling system and look for leaks. ( about 15 PSI is the general limit ) If you suspect a combustion chamber leak, after doing a pressure test turn the engine 2 revolutions by hand. If a cylinder has filled with water cranking by starter motor can bend a rod.

One thing with this exhaust tester is the suction bulb used. With the engine running squeezing the bulb draws in the fumes from the system filtering through the specific blue water which if the fluid color changes there is a problem. Also if after pumping the bulb flattens out then this shows that no additional fumes are entering the system.

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91 300GD SWB with transplanted 87 OM603 turbo motor

In a perfect world, the coolant hose should not be pressurized when engine is cool, cooling system is a closed system. It only get pressured when the system is at temp. That means you have a very minute leak from the Head Gasket interface. If engine is not overheating and only losing a bit of coolant every week then put up with it.

Change to lower pressure cap would help. The real fix is to change the HG. I drove my SDL for 4 years like this without problem. I changed the HG eventually but for different reasons. My engine seized with lack of oil, oil chain snapped, and it had nothing to do with overheating. I would ignore it for now until it gets serious.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

Let me rephrase it. I had no problem during normal driving. The car overheated in Death Valley where the ambient temp was at 120F. I wired the Aux fan to be on all the time to get home. I would add a switch to turn on the Aux fan just in case.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

Great thanks for all the input.

Mark

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91 300GD SWB with transplanted 87 OM603 turbo motor

I used the same gas analyzer. It did not detect the combustion gas on an overheating, and coolant spewing, engine. All other symptoms pointed to a leaking head gasket. After I eliminated all other possible causes, I replaced the head gasket and that fixed the problem.

I agree, that if it is not overheating, or spewing coolant, I would just drive it. It might die of something else before the head gasket leak needs to be addressed.

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Greg
2012 S350 BlueTEC 4Matic
2007 ML 320 CDI
2007 Leisure Travel Serenity
2006 Sprinter 432k
2005 E320 CDI
1998 SLK230 (teal)
1998 SLK230 (silver)
1996 E300D 99k, 30k on WVO
Previous:
1983 240D, on WVO
1982 300D, on WVO
1983 300CD, on WVO
1986 300SDL 237k, 25k on WVO (Deerslayer)
1991 350SDL 249k, 56k on WVO - Retired to a car spa in Phoenix
1983 380 SEC w/603 diesel, 8k on WVO
1996 E300D 351k, 177k on WVO

Is the exhaust tester sensitive to Diesel exhaust? Maybe compression leaks before combustion?

What's the cylinder head casting number by the #2 injector. Should be of the form 603 016 XX 01. XX are the critical digits discussed on this forum.

Sixto
87 300D

#14. Yes it does test for diesel as well. It's a nicely built tester. I got mine from NAPA.

Mark

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91 300GD SWB with transplanted 87 OM603 turbo motor