Disappearing Coolant 300E - PeachParts Mercedes-Benz Forum

JEdwards · #1 01-06-2008, 04:57 PM

I have read the posts about vanishing coolant on the 300E, but I still have a couple of questions.

my car: 1987 300E, m103 engine - approx 206,000 miles

It seems that the place coolant goes is out the exhaust if you need a head gasket, and that as a result the coolant and oil will mix. On my car (m103 engine), the coolant is just disappearing, not at an alarming rate, but needs to be topped up after long drives or a couple weeks. I've inspected the coolant and found no oil, and the oil shows no signs of coolant, yet there is the anti-freeze smell in the exhaust when the engine is up to temperature. Is there any other way for the coolant to get into the exhaust apart from the head gasket?

I also have noticed "wetness" on the passenger side of the engine originating from the valve cover seal over cylinders #1, 4, 5. Could this be the source of the problem with the coolant and it somehow is getting into the exhaust headers at the same time (perhaps through those gaskets)? The only reason I ask is because not long ago my exhaust broke putting stress on the headers and maybe loosened the gasket.

Thanks for your help.

heespaul · #2 01-06-2008, 06:32 PM

My sons 300E was running warm and overheating. I would add water/coolant and 2-3 days later add again. I saw no H20 leaks and was completely baffled. Well finally, you know what happened. On a very hot day in LA, the car starting to blow steam out of the exhaust. Luckily I stopped the engine quickly and saved the motor. "Long story shortened". After removing the head I discovered there is a engine block water drain plug/petcock that is located under the exhaust manifold at the rear of the block that I could see or be seen, at least I could not see it, until I removed the head. The water being lost form this plug/petcock was leaking at he same firewall location as the AC condensate. The plug had rusted through and progressed to constant water loss. I suggest do not drive the car, try to look way up under the car under exhaust and see if this is it. good luck Paul in LA
89 420SEL
89 300E
93 500SEL
65 Mustang Fastback
2002 Explorer

cummins · #3 01-06-2008, 10:13 PM

The head can still be the culperate, water can still go down the exhaust and not get in the oil. If the gasket or head are leaking into teh cylinder at a rate slow enough, the water will pass through the cylinder just as the air does. If the car still has the catalytic converter under it, the water will be evaporated and you will not see a sign or usually no smell.

With the engine off.

What you can do is get a cooling system pressure tester and pressurize the cooling system, it should hold pressure. If it doesn't, go to your tail pipe and listen for air noises. If it is only one cylinder that is leaking, it may be necessary to rotate the engine while trying to hear air. You can also pull your oil cap and listen for air coming from the crankcase, But usually if that is the case, you'll have oil and water mixin with evidence.

abe g · #4 01-07-2008, 01:10 PM

It may seem elementary but a good stop leak should be tried. I had an old chevy that leaked at freeze out plug in rear of engine (under flywheel?) Kept it going for years with stop leak occasionally. worth a try, good luck, Abe g

cummins · #5 01-07-2008, 03:24 PM

Quote:

Originally Posted by abe g

It may seem elementary but a good stop leak should be tried. I had an old chevy that leaked at freeze out plug in rear of engine (under flywheel?) Kept it going for years with stop leak occasionally. worth a try, good luck, Abe g

Stop leak additives can plug heater cores and small water passages though. Good idea if you are fixin to sell or get rid of it, but if it's a keeper, try and repair it correctly for years of reliable service.

JEdwards · #6 01-07-2008, 05:32 PM

Today I couldn't get the car to start (unrelated problem?), so when I came home, I inspected the engine area with the engine running.

I could not smell/see any exhaust anywhere around the block (so no crack in the block then...) and in doing so I saw this drain plug. Plug is intact and there is nothing leaking/no wetness anywhere around it. In fact, the only wetness anywhere around the block at all is on the middle of the head from the slightly leaking valve cover gasket.

Apart from the pressure test/repeated visual inspections, I would only guess that my head gasket is the vanishing coolant culprit.

Out of curiosity, with a small leak like this one, is it acceptable to drive the car around without risking catastrophic engine damage?

cummins · #7 01-07-2008, 11:45 PM

I wouldn't drive it unless it was an absolute thing that you had to. The problem could get much worse fast, very fast!!! Another thing you could do is pull your spark plugs out and see if any of them have little crystal lookin type build up, if so that is the cylinder that is burning water. I spaced that check out and just thought of it.

JEdwards · #8 01-08-2008, 09:34 AM

I'll pull the plugs today and see if the cylinder is burning water. If it is, does this indicate the head gasket as the issue? Also, how fine will these crystals be, visible to the naked eye, or should I get something to examine them closer?

david s poole · #9 01-08-2008, 09:40 AM

have you checked to make sure that fan clutch is locking up?

JEdwards · #10 01-08-2008, 12:08 PM

No, I haven't checked that, how can I check the fan clutch to see if it locks up?

yal · #11 01-08-2008, 12:33 PM

Sometimes the water pump leaks and seeps down the side of the engine but burn off before it reaches the ground. Are you smelling any coolant?

cummins · #12 01-08-2008, 12:44 PM

the crystals will be visible with the naked eye and they'll be white in color. The gasket is teh most probable cause, a cracked head could do the same though.

To check the fan clutch, put a short piece of string on the fan then start the motor. If you can hold the fan from turningwith a firm grip, the fan clutch is bad. if it pulls the string out of your hand, it's good.

brabus3.6 · #13 01-08-2008, 02:59 PM

My vote is for the head gasket. This has happened to me twice although my engine is of slightly higher compression. Your local garage should have a combustion gas tester that they can replace the water cap with to check this. This has a chemical inside it which will change colour if exhaust gas is present in the coolant.

I never saw oil in the coolant, the fire rings failed allowing combustion gas into the waterways. Do your valve seals (and probably your guides to at that mileage with the head off) too and remember to check your head for flatness.

JEdwards · #14 01-08-2008, 05:50 PM

I pulled one of the plugs (on cylinder #2) and checked for the crystals... there weren't any to be found. I also snagged my mom's Nikon SLR and took some pictures so you guys can see where there is fluid leaking.

In the first picture, I just want to point that although the "oil" goes from the valve cover to the bottom of the block, the valve cover isn't the only place leaking oil - it seems to be also coming from where the head meets the block. I have more pictures I can upload of this if it helps.

The reason I question the head gasket is because there seems to be another gasket (?) listed on the DIY links page for the cap/rotor and I wasn't sure if perhaps this could be the problem.

As far as the valve guides go - I am looking at the parts online right now and there are two categories, "std" and "1st" - which of the two should I purchase, and how many? 6 of each?

One more question - as far as parts go, I know I will need the following:

-valve stem seal kit
-valve guides
-valve cover gasket
-head gasket kit

is there anything else that should be on the list?

cummins · #15 01-08-2008, 07:52 PM

There is a cover gasket set for that oil leak, it is seperate from the head gasket.