Hi All:

You Gasser guys will probably say "I told you so". But, Hey, I own a Gasser too.

I think I've found a serious design flaw in our beloved Diesel. And why it's imperitive that we use synthetic oil. I just finished a rebuild on a spare D24T that I intend to use as a backup for my 760. After finishing the rebuild, I did a Compression check. I previously screwed a gauge in place of the switch to monitor oil pressure. During the compression procedure I was monitoring the gauge, No OIL Pressure. I wasn't overly concerned, at the time. As I liberly applied straight STP to all the bearing surfaces and Cylinder Walls during the rebuild. Also I prefilled the Oil Filter but probably not enough.

Well, I decided to bench run this engine. I read a post from Badge988 earlier and considered this an excellent idea. Bench running picked up a few problems that would have been monumental if the engine was installed. (Thanks Badge) I made it a point to monitor Oil pressure. It came up after a delay and was where it should be. So I still wasn't concerned. After all, cranking speed is 300 rpm. Normal idle is 830 rpm.

I just had a recent discussion with Badge988. He told me he had an oil pressure problem, where his rebuilt diesel was running for 3 minutes with out oil pressure. He said the car was on an incline with the nose facing up. And the fast idle was turned down. This turned on a light, I said "I remember this problem". I decided to bench run my spare again and monitor the oil pressure. It built up but took longer than I'd like to see. (Thanks again Badge)

Well here's my thoughts on the matter (I suppose alot of you are saying "finally, get on with it!"

The D24 has a rather strange oiling system. It has a Crankshaft mounted oil pump, with a long Suction Tube. The pump is mounted in front of #1 Main Bearing and the oil pickup screen is way down in the sump by #5 Main Bearing. This suction tube has to close to 36" long and has an inside diameter of approx. 3/4". I'm not a mathematician, but it's obvious there's a lot of volume to be filled before the pump ever gets primed. And you'd better have a good pump to pull a suction. To make matters worse there is approx. 6" between the level of the pump and the oil level. In Badge988's case it was even more due to the incline. That's a considerable suction head for a heavy liquid. Most american engines that I have rebuilt, have the pump located close to oil level or submerged.

Now when the engine was new and pump clearances were tight. Oil delivery was probably was not a problem. After thousands of miles, clearances increase and pickup time increases. Multiply these dry starts by thousands during the engines life and you get reduced engine life (One of the complaints of this engine). If you ever had one of these engines apart. You'd be amazed at the quality of construction. It's true German Construction, in every way.

I could never figure out why Synthetic Oil worked so well on these engines. After all Truck Drivers were using the likes of Rotella Dino 15W-40, and getting 500,000 miles without a rebuld. Well it all makes sense now, with Synthetic Oil's superior lube qualities. It's able to handle dry starts better. Hence, longer engine life in our D24's.

Now this does not correct the original problem. It's only a good a work around. Probably the best thing one could do is replace the pump during a rebuild. and switch to synthetic. I have yet to replace my pump but will do it now. I'm afraid even a new pump will not completly aleviate the problem, hence the design flaw.

I've been around large stationary diesel engines all my life. They all have a pre lube oil pump that comes on before startup and goes off when the engine starts. Of course we are speaking of much larger suction volumns that necessitate this. But the concept is the same. A small pre lube pump in our D24's. Timed to come on and off with the Glow Plugs would completly aleviate the problem. I am going to research this with my spare engine and report the findings.

I guess some of you will probably say "Jeeze, get a life". But I'm retired now :-). And love to keep busy on one of my favorite pastimes, D24T TURBODIESELS. It keeps me young, but my wife can't stand the smell. She always yelling when I work on it :-). Does that sound familiar guys?

I took enough of your time with my rambling, any thoughs or ideas?