Newbie looking for hot start opinions

[mikeyg1975]

Hi everyone, I am new here, I recently purchsed a 1993 one ton quad cab dually and have done a lot of work to it since I have owned it. I am a mechanic/machinist by trade and used to work on semi trucks, and engine machine shops but now work in the oilfield. I have limited experience when it comes to the pre-cup engines and I know there is a ton of threads on this subject already, however, I feel as though my situation is unique. Since I have owned this truck, I did a full engine tune-up that included a rebuilt DB-2 injection pump from US Diesel, Rebuilt Injectors from SS Diesel supply, a new turbo, 4 inch turbo back diamond eye exhaust, and new AC Delco glow plugs, I bled all of the air out of the injection system and when the truck is running, it runs great, while I had the glow plugs out I did a compression test and even though I had some deviance between the cylinders, I was showing 400-425 psi per hole. The problem I am having is it starts great when cold, but will NOT start when it's hot, without bypassing the glow plug controller with a manual switch and relay, push the manual switch for 5 seconds, fires right up. Now why would a hot mechanical 6.5 require glow plugs to start?? Especially with a fresh pump?? It has a new lift pump, new glow plug controller, and new oil pressure switch as well. Officially color me stumped!!

[DmaxMaverick]

Welcome to the Forums!

Try to keep it simple, as I believe it may be just that.

Any 6.2/6.5, EFI or MFI, does not require glow plugs to start hot, but there are several factors in play that make that true. It depends on what "hot" means. If your compression test has all cylinders north of 400 PSI, then no worries, there. Cranking speed is important to a successful start, in any case, and that relies on a healthy starting/charging system. Cranking with all the glow plugs removed is far and away from cranking under full compression. This may indicate a weakness in the starting circuit, somewhere. Weak/mismatched batteries, expired battery cables (they can fail internally, even when they appear pristine externally), and/or poor grounds, are the most common.

Also, your new glow plugs are likely AC60G, which do NOT (contrary to common belief) heat as well as most other plugs. They may be cycling, but not long enough to provide enough heat for a start. It is not uncommon for a 6.5L to need some GP heat for a hot start. My previous 95 would not start w/o a GP cycle, under any circumstances. I used Quick Heat plugs (Kennedy), so the GP cycle time is essentially moot. They fully heat in less than 5 seconds, while the AC60G's can take as long as 15-20 seconds to reach full heat.

If your electrical system is healthy, and appears to crank as well as it should, you can either count on using your GP override, modify the GP cycle time, or replace the plugs with faster (Quick Heat) plugs. Pushing a button is free, the others are not.

[AKMark]

My 99 6.5 always needed at least a few seconds of glow time regardless of how warm it was.

It ran great once it had the glow....So it had a push button as well.

[Dvldog8793]

Ditto on the AC60gs. They may be tough but my 1996 would not start when it was south of 20* with new 60gs. I installed some quik-heats and it fires everytime now no matter how cold or hot. Same issue with my blazer, it has a button and the cycle time went from minimum of 20seconds on a cold day to about 7-10 with the quik-heats.

Good luck