1982 240D won't start when hot

[kosinski]

I bought this l982 240D in non-running condition. It had broken camshaft bearings caused by the camshaft sprocket falling off. I replaced camshaft, cs bearings, sprocket and rocker arms. All bolts properly torqued down. Engine started up instantly and ran well with good idle and normal smoke. After taking the car for a spin, I shut off the engine and it would not restart. Only after cooling down to about 60 degrees would it start. I have done this several times and the engine simply will not start when hot. Once it cools it starts normally. I'm stumped!! Any advice will be appreciated. Jerry

[darrellws]

Jerry, when you say it will not start does that mean that the starter will not turn the engine over or it will not fire?

Darrell

[Brian_Wall]

You could try a leak down test. If the cylinder walls are warn you may not have good enough compression to start hot. When the engine is cold the block contracts and you get a better seal between pistons and cylinder so the car starts. Once running the engine idles at a high enough RPM to keep the compression up (not enough time for leak down) so it keeps running. When you stop and try to start hot the starter does not turn the engine fast enough to create compression needed to burn the diesel because each cylinder is leaking a little.

Also, are you sure the valve timing is right? When you put on the new camshaft sprocket, if you are off by one tooth this could help reduce compression. The 240D engine can start and run normally even if you are off by one tooth as long as the pump timing is right.

Brian Wall
1974 240D

[darrellws]

Brian, if the timing is off by one tooth the valves will hit the piston and break the camshaft. One tooth = 18 degrees.

Darrell

[kosinski]

the starter turns the motor over normally, but with not even a hint of firing when the engine is hot; almost like its not getting fuel. Since it starts so quickly when stone cold, its hard to blame it on poor compression or leak by. Valve timing is correct, I'm sure of that; however, I did not change injection timing from what it was set at. Jerry

[darrellws]

Jerry, this is far out but when it won't fire the next time remove the fuel cap and listen for a change in air pressure. Is the tank full, half or near 'E'? With the cap off see if it will fire up.

Darrell

[Brian_Wall]

One tooth is 18 degrees. I am no expert and I am sure Darrell knows more about diesel engines than I do. However, I can tell you my experience with my 240D last year. I took off the cylinder head and when I reassembled it I was off by one tooth. The car started and ran fine with no smoke. Then I discovered the valve timing was way off. I moved the chain one tooth turned the engine by hand, no problem. I started the car and again it ran with no smoke. I was VERY surprised at this. I put the timing back and sure enough the car ran. The biggest shock to me was that there was very little difference in the sound of the engine and amount of smoke produced if you are one tooth off. As an experiment I moved off by two teeth. I turned the engine slowly by hand and it stopped. It seems the piston hits the valve if you are two teeth off. My conclusion is that if your valve timing is way off but not far enough off to have a valve hit and the pump timing is right, the engine will run normally as long as there is enough compression to burn the diesel. But you cannot have maximum compression unless the valve timing is right.

I do not think injection timing is your problem. If the pump timing is off enough to make your car not start you would see lots of smoke when it was running. I tried this experiment on my car too.

I have herd a Mercedes mechanic that I know and trust talk about how a Mercedes diesel can start normally when cold and be very hard to start when hot due to cylinder ware. He gave me the explanation of heat expanding the block. However, I have not seen this first hand and I don’t know if the 240D has this problem. It seems to me that a leak down test would a good test to do just so you know that you have a good tight engine with good compression.

I think that your problem must be caused by loss of compression for whatever reason or loss of fuel delivery. You might try removing one of the injector lines when the car is hot and will not start. Have someone try to start the car and see if the pump is delivering fuel as the car tries to start hot.


I agree with Darrell that removing the fuel cap would be a good test to try also. Perhaps the problem is not related to temperature. Maybe when you run the car a vacuum develops in the tank. When you stop and try to restart the fuel pump is not turning fast enough to fight the vacuum. When you wait for the car to cool the vacuum leaks out of the tank and then the car will start. Darrell, is this what you were thinking?

Brian D. Wall
1974 240D

[darrellws]

Brian, you are on the money!

Darrell

[Steve Clark]

Had a similar encoumter with my 300TD a few years ago.Same symptoms-great initial start in the morning,and then a real reluctance to restart after driving for a while.The tank's vent system had a plugged vent valve.Found this after realizing the primary fuel filter had emptied:I could see that air was going back to the tank via the fuel line.

[kosinski]

thanks Darrell, Brian and Steve for the advice. I started the car this morning and ran up the temp. After it was warm I removed the fuel cap, no sound of air. The cap is vented properly, I could easily blow air thru it. Once again it wouldn't start. I replaced the small primary fuel filter and lo and behold it did start but just barely. I intend to change the cannister type fuel filter next but have to fix the hand pump first. While trying to hand pump air out of the system the O-ring around the top of the plunger fell off and fuel is leaking badly. Will do that tomorrow plus change secondary fuel filter. Will let you all know what happens. Jerry

[kosinski]

Well, I fixed the hand pump and replaced the cannister fuel filter but that didn't solve the problem. I took it for a drive and it would not start when hot. Maybe I'll look into compression next. Somehow, I feel its a fuel problem but not sure. Any more ideas would be gratefully heard. Jerry

[Palangi]

Sometimes hot start problems are caused by a bad starter. If it has a few winding turns melted together it won't spin the engine fast enough to start. If a non-Bosch rebuilt starter has been installed, I would almost guarantee this to be the problem.

[vbishop]

I've got a similar problem with an '83 300D. The starter works fine when I first start the car up when the engine is cold. Once it is warmed up, sometimes the starter won't even engage. I just get a click. If I let it cool down for about 15-20 minutes, it will start fine. I'm pretty sure it is not the transmission interlock. Anybody have any other ideas?

Vince

[jtripp]

I would check the valve clearances. They may not be seating fully when hot. You did not mention adjusting the valves when you replaced the camshaft and bearing stands.

If the engine starts fine when cold the compression and piston fit only gets better when the engine is at operating temperature.

[joeym7]

jerry check the anariod compansating valve and see how many shims are undre it if any. also if thieir is a vac line to it is it getting it on crank.joeym

[littleridge]

Are you sure the glow plugs are coming back on when engine is warm/hot?

[darrellws]

Is the starter turning the engine over?

[Lynda J]

Check the fuel tank for alga. If the screen in the tank sucks alga into it it won't start. ONce the car sits for a while the alga will release and it will start. Then as you drive and suck fuel through the system you have problems again. Try back blowing the tank.
Run it and let it not start. Then take air pressure and a rag and blow air in through the fuel tank neck. See what happens.

Hate to say it but you could also have a bad injection pump.