Ok, I don't know much about the D-Max.

I just found out that they have 17:1 pistons. What did GM do to allow easy cold starts with such low compression?

My guess is that it has something to do with the common rail injection and the electronics, but I really don't know. :(

Help?

Bill

1000W glow plugs. They get the internal temp of the cylendar(sp?) up pretty quick. Between that and an intake air heater they dont have many problems with cold starts.

Basically, common-rail injection pressures are typically 18000psi and up - the sprayed mist droplets are much smaller, and ignite easier.

PCM begins injection with minimal amount of fuel to get combustion started, increasing the rate as combustion temperature rises, then tapering off as required by demand.

Thus, you don't get the tremendous rattle as combustion goes berserk on the full load of injected fuel, as in our engines, and which makes cold-starting somewhat more difficult in the mechanically-injected engines, including the PCM-controlled versions.

not really glow plugs or common rail technology.


99% of the reason is indirect vs. direct injection. Direct injection can run a significantly lower compression ratio. The old 12 valve cummins's were about as basic in terms of diesel technology there is, but they still only run around 17:1 because they have always been direct injection.

The direct-injected mech inj 12-valves are harder to cold-start than the common-rail EFI 24-valve versions, even tho both have intake air heater assemblies.

The 6.2\6.5 indirect-injected glow-plug configuration was chosen because of ease of cold-start and good cold drive-away.

The 21:1cr was chosen to augment the glow plugs with quicker pressure rise to combustion temperatures - again for cold-start and cold-drive-away.

The 6.5 is a lite truck engine, available in the 1500 series, and most of the public that would drive the then-new Diesel option could not even spell Diesel, much less put up with the hassles of owning and driving one.

Not many Suburban-drivers would even want to Wait to Start, in their hectic daily soccer-mom routines, much less search for quality fuel.

The quick-starting indirect-injection with glow plug and high compression was chosen for ease of public-acceptance, when GM was given congressional-mandate to improve lite-truck fuel economy into double-digit area, or lose the 350 and 454 workhorses.

Also allowed combustion with really crummy fuel, and multi-fuel use by the military.

When I start my dually in the cold it fires right up and only has 1 battery(instead of 2 like it should). Draw on it seems less than the two batteries in my suburban. I am guessing that the glow plugs don't draw as many amps in teh dmax as in the 6.5. Just an observation.

Lower compression. It does not need two batteries because of compression.