Finally completed head gasket/valve job...here is the quick version of the blow-by-blow...

November...put in new thermostat (Febi), car runs hot (95-100 c). Put in another thermostat (Behr), car still runs hot!!..check coolant...little bit of engine oil; check head space in coolant reservoir...carbon monoxide present. Diagnosis-bad head gasket.

February...car has 268,000 miles. If I remove head for head gasket, I will do valve job/guides. Instead of doing valve job on my head, I decide to get rebuilt head from Cylinder Heads International (Texas) for $350.. (This to avoid down time on my main ride.)

March ...all set to do the head "switcheroo"...I pull the pre-chambers out of my car (head still in place) to check for damage. They look good....I just happened to try how the pre-chambers fit in the rebuilt head sitting on the kitchen table...THEY WONT GO IN!! Tip of pre-chamber = 16mm diam, hole in head = 14mm diam!! As it turns out, the head I recieved was from a non-turbo 300D...has different pre-chambers.

I call CHI and they say they have the proper head with bigger pre-chamber holes, from turbo....they will machine and send out that day!!!

April...I recieve second head...valves are terrible (wrong machine angle (45 deg instead of 30), valve edges sharp, chewed up. Also, mating surface (machined) very rough...fingernail-catching grooves. I take valves from first head (which look good) put in second head, lap them in. I take a chance, assume the mating surface is ok (even though that little voice inside said otherwise)..and I installed the second head.

Result: car runs ok, but still runs hot (95-100), with major residual pressure in coolant reservoir in the morning...conclusion - rough machined surface of head not sealing properly with head gasket.

Note I still have two extra heads on hand ...the first incorrect one, and the original from my car.

I now decide to get a valve job done locally on my original head, then return both rebuilt heads to CHI for a refund.

Valve job done at reputable shop with lots of experience on Mercedes, including diesels...here is cost breakdown:

Dissassemble and hot tank head .....$60
magnaflux head................................$40
Grind valve seats..............................$175
Remove and replace 10 guides (labor $10 ea.)........$100
Ten guides (parts, $6.80 ea.)...........$68
Size 10 guides ($4 ea)...............$40
Resurface cylinder head...........$60
New valves -
5 exhaust valves @ $37.80 ea........$189
5 intake valves @ $29.40 ea............$147

tax....................................................$20.20

TOTAL..............................................$899.20

WOW!!!!!!!!!!!!!!!!!!!

Early May - Take off bad head, put on good head (note...all work done in my driveway, hoping for good weather, no enthusiasm to repeat what I just did a few weeks earlier.)

Result.......Great! No residual pressure, no oil in coolant, no carbon monoxide in coolant reservoir, car runs great. HOWEVER...it still runs hot...95-100 with a few peaks to 110!!!!!!!

A few days ago...I took out the Behr thermostat, put in an Auto Zone Wahler.....PERFECTO!!!!!!! Car runs at steady 85 deg C.

Finally, life is good, car runs great, no residual pressure, good coolant temps. etc......finally out of the doldrums, still hurting in the wallet.

(As part of this process, I also replaced all coolant hoses, oil cooler hoses, gasket on oil filter housing, and a few other things)

Now to tackle body work ...rusty doors on passenger side.

What an ordeal!!!!!!!!


Mark M

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1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)