Duramax coolant flow diagram?

[killerbee]

This is no remark toward any individual, just a comment on custom tuning. i have been reading about some of the large pulse widths, in combination with some pretty staggering timing advance numbers. In my own tuning, I have had caution buzzing in the back of my head, with the realization that this is a potentially lethal combination for cylinder pressure.

What happens is that this combination my be pseudo-ok for quick launches, and dyno indications, and otherwise non-heatsoak motor conditions. But when the throttle is left open (forgive the gas analogy) for more than a few secs, as in plowing, or towing, that same timing starts really escalating cylinder pressure, due to the ignition advancing effects of load and heat accumulation. Combustion occurs sooner in a nutshell. Peak cp's increase and advance as the load is held constant.

It drives home the importance of tuning with some kind pressure sensing equipment, under real world stress, off-the-dyno type monitoring.

I guess what I am saying is that longevity is traded off much quicker with tunes that do not compensate for dynamically changing heat and load conditions, but especially heat. After working with the EFI gang for a couple of weeks, they finally got these "compensation" tables revived for me personally on all OS's, so folks can start using them (they were inert from the factory). However the "MAP timing" compensation table is still inop, we may have to wait for that one.

[Mark Rinker]

You might take your findings and apply them to the C4500 series. The placement of the engine is entirely different, but I have run across two or three 2005 LLY equipped units with engines replaced already under warranty. One in particular had two turbos replaced before the new warranty engine.

[killerbee]

I have run across two or three 2005 LLY equipped units with engines replaced already under warranty.

what was wrong with them?

[Mark Rinker]

Don't have details from previous owners, just the service history from VIN searches. It would appear both died from prolonged towing while overheated. Turbos, pistons, etc. C4500s are rarely used as daily drivers. Always towing/hauling at higher RPMs due to lower gear ratios.

Personally, I am shopping for LB7s only. Can't take a risk on getting someone else's overheated problem. It seems like there are lots of '05 C4500s for sale, more than any other model year out there...

[carco]

Ok, this may not be your answer but I ran across this and it may help someone.
Cold start, both t-stats closed, coolant pumps to oil filter-flywheel houseing cross over-block-heads-EGR and heater core @ 26GPM. Engines warms to 180* first stage of the primary t-stat allowing some flow to the radiator. At 185* secondary t-stat starts to open flowing more to the radiator. In here @ arond 132* the turbo starts recieveing coolant through a thermo controlled circuit by-pass. At 203* the primary stat is full open. At 212* the seconday stat is full open, all coolant is through radiator and flow is near 80 GPM. Now this is for the LLY engine. bob.............

[killerbee]

off-topic. It is odd that the turbo cooling begins so late. I would guess that it is important that the turbo not be thermally shocked. This was a real concern in turbocharged Cessnas, there were air cooled.

[rob from bc canada]

I do not profess to be knowledgeable in engine technology, but I would expect that running a Diesel at high hp output (towing) with a leaking headgasket would very quickly blow or melt a bigger hole through there, and start warping head or block beyond repair.

Can't imagine it'll get you very far once that starts to happen, and could leave you stranded with little warning, or lead to engine on fire.

If you know which cylinder is low on compression, and you want to squeeze a few more miles out of it, what would it cost to have a small shop install a new gasket just on the one side only?