Mechanic says significant blow by... - PeachParts Mercedes-Benz Forum

jprocess · #1 10-06-2004, 11:34 AM

I brought a 1979 300CD to a local MB mech. I'm thinking of buying the car. He tells me theres a considerable amount of blow by and he's concerned the motor may not last another 50k.(Then again, he says, it might last another 100K...He just can't say) I pulled the oil filler cap and there is quite a bit of smoke coming out. Question is: how much smoke is normal to be coming out of the valve cover for an engine that might have 300K on it. (speedometer's broke @ 170K). Is rebuilding the entire engine necessary or can a valve job work(or is that basically the same thing). Basically I'm looking for options.

The engine starts right up. No noticable smoke at start-up. Good power and reasonable accelleration for this car.

It has the usual wetness at the valve covers and is pretty wet underneath. However I just found a line from the valve cover that goes to the air filter that was disconnected and was leaking all over. Who knows how long this has been like this..?

Thanks for any help
Steve

Eric Eliel · #2 10-06-2004, 12:12 PM

The inexpensive test to determine the condition of a diesel engine is "will it start right up in cold weather (after sitting all night)"

Blow By is difficult to measure unless you are utilizing a spare home gas meter AND Mercedes has a spec for blowby in CFM (I just don't remember what my MB diesel mechanic told me).

The blow by could be caused by caked up rings from a poor oil change interval AND this sometimes can be reduced by utilizing synthetic oil over a period of time.

If the engine starts right up in cold weather, I wouldn't worry about the blow by. AND just because it doesn't start up in cold weather doesn't mean the blow by condition has anything to do with the problem.

(Now if you wanted to spend some money on a leak down and compression check, that would give you much more information as to the engine condition. But that wasn't discussed in your post) Thats the proper way to diagnois an engine's condition.

dieseldiehard · #3 10-06-2004, 03:10 PM

You may have a cracked ring (I did in my '79 300TD) or the cylinder bore has worn to the point you need an engine rebuild (more likely, I also had that problem w/ my '79 at 279K and spent $5K installing a rebuilt turbo engine in it).

I would walk away from the car before you get too far into it. Finding a low mileage engine for the car (a non turbo) is going to more difficult than finding one for a turbo. You will probably like a turbo model better too especially if it has the later style climate control (not the best system either but still easier to find parts for).
Dieseldiehard
1971 220 (gas) 4-spd manual 106441
1979 300TD w/ ’85 turbo engine 295530
1983 300D 243280
1985 300TD 217300
1987 300D 258230

Hatterasguy · #4 10-06-2004, 07:35 PM

At almost 240k I can put my hand over the oil fill port and not feel much of anything. Other then the came lobe throwing up a few drops. Blow-by is death to diesels unless the car is dirt cheap or in perfect shape I would pass.

engatwork · #5 10-06-2004, 08:51 PM

You can take a brand new rebuilt 617 engine and it will have some blowby.

I'm with Eric here

Quote:

If the engine starts right up in cold weather, I wouldn't worry about the blow by.

To me this is a good indication of a healthy engine or not.

jprocess · #6 10-06-2004, 08:56 PM

Well... Living in Florida I'm not going to have to many instances of starting in cold weather.. and it won't be for a while till I have the opportunity to test that either.

Still not sure what to do... Any one else want to chime in....

BTW.. the current owner "says" there was a compression test done on it just 6 months ago and it checked out fine... I don't have any proof of that.. although I don't have any reason not to believe him. He's been straight up about this possible transaction all along.

Thanks
Steve

Hatterasguy · #7 10-06-2004, 09:22 PM

Get a compression and leak down test done, that would give you a real good idea of what you have.

psfred · #8 10-06-2004, 09:45 PM

Dollar to a donut the crankcase ventilation line was disconnected to eliminate the blue smoke behind the car. All the oil now going to the road was going down the intake.

Pass unless you want to rebuild the engine.

Peter

jprocess · #9 10-06-2004, 10:17 PM

The ventilation line was disconnected... reconnected it.... still no smoke.

whunter · #10 10-06-2004, 10:53 PM

Hello Steve
Insufficient data...
What is the cost?
Can you post pictures, both sides of engine, interior front and exterior + special attention on rust spots?
Then we may be able to guess at weather you are wasting money or getting a fair deal.

jprocess · #11 10-06-2004, 11:08 PM

Well he wants 3200$ The only rust is on the underside of the drivers side door towards the front. About a 4 inch spot.

I'll get pics of the engine tomorrow. These are the only ones I have right now.
The seats need to be recovered. No tears in the headliner although it looks like its 25 yrs old. Some window switches need replaced.

Heres the link http://www.geretygraphics.com/benz Sorry I didn't have a chance to resize them.

TwitchKitty · #12 10-06-2004, 11:12 PM

First start of the day try to start the engine without letting the glow plugs heat-up. The engine should start after it turns a few revs. - Poor man's compression test

jprocess · #13 10-07-2004, 12:10 AM

bump....

turbodiesel · #14 10-07-2004, 12:20 AM

Too much money. You can get a REALLY nice turbo coupe, 82-85 for that. Being your from Florida, you don't really have to worry about rust.

dieseldiehard · #15 10-07-2004, 12:33 AM

too much money in my book too.
But rust, that can be a problem anywhere, a car from NJ could be sold in FL you know. Just look out for the stuff! IMHO FL leads the nation in rollbacks. just look at some of the low mileage cars dealers are selling in FL on eBay. . . .
I wouldn't trust a one of them!