GM-GMC: 6.2 diesel, diesel mechanics, gm diesel

Question
I have a 83 gm diesel truck, when the truck is cold I can start it and drive for a hundred miles no stalling or any other problems, but when I shut it off and leave it for 15 minutes and try and start it , it won't. It turns over at normal speed but it doesn't start. I was told to change the batteries, the cables, the glow plug relay,the injection pump coil, the filters, the fuel pump on the side of the engine. nothing changes I love the truck but when I have to let it cool down for a couple of hours before it will start again it is annoying. I asked several so called diesel mechanics and all I have been doing is changing parts that were fine. The truck has 126,000 actaul miles on it and has been well mantained. PLEASE HELP me get my tuck back.  Thank You Robert  

Answer
Robert,

I am afraid that your problem is an expensive one.

The GM 6.2/6.5 L diesels have their injection pumps mounted in the worst possible place.  The "valley" of a V-8 engine is the hottest location, especially after shutting the engine off.  After engine shutdown, the temperature actually rises and "hot soaks" the parts located there.

Diesel fuel is an oil, albeit a very thin one.  When the injection pump gets hot and, after many years and miles of service (the internal parts become worn), it cannot build enough pressure to make the injectors open.  When the engine cools off, the fuel gets a little "thicker," the internal clearances in the injection pump tighten up, and the engine will start.

There is a simple test to ensure that the injection pump is causing the problem.  After shutting down the engine, and confirming that it will not start hot, pour some LUKEWARM water over the injection pump.  You may have to repeat this process a few times, but if the engine starts when you cool the injection pump off, you have found the problem.  NOTE:  You can damage the injection pump if you use this procedure and the water is too cold.

If you do not want to perform the test, the injection pump will need to be removed and tested.  It will likely need to be rebuilt or you can buy a rebuilt pump (and even new ones) from eBay or from diesel injection shops.

Your injectors probably should be replaced or be rebuilt, too.  Though they are not the problem in this case, their spray pattern degrades over time and that causes the engine to lose power and economy.  You can get them tested at a diesel injection shop, and some shops will test them for free.

Price the parts and labor before you proceed.  You may not want to spend the amount of money it is going to take to repair the vehicle.  I like my 6.2 diesels, but I do my own work so I can afford to keep them going.