6.5 dual stat cooling upgrades back in stock!

[Kennedy]

Just like the title says, we now have the kits on the shelf once again. There are some "out in left field" vendors out there who seem to think that a single stat and restricting the bypass is the answer, but I'll say it point blank nothing could be further from the truth.

[ronniejoe]

I have also advised several people (who have asked me) to avoid the bypass restrictor that is out there. This is a horribly bad idea.

[Robyn]

These clowns with the ANTI DUAL STAT BS have got to be Smoking something...

I agree 100% with John and RJ...

The better coolant flow with the dual stat setup is likely the single most beneficial change in the 6.5 cooling system ever made. (PLUS THE HO PUMP)

The new heads produced by AMG are certainly a game changer when it comes to having better flow in the heads.
When I built the last engine for the Dahoooooley I used an AMG block and AMG heads and then reused the single stat xover and the standard pump (Pump was new)

The rest of the cooling system was fresh. The AMG engine has always ran much cooler than the GM iron ever did..
GOTTA BE THE FLOW THROUGH THE CASTING ?????

[sctrailrider]

Yea once my P400 is done I will be looking into this more...

[trbankii]

There are some "out in left field" vendors out there who seem to think that a single stat and restricting the bypass is the answer

Yet I'll pretty much guarantee that not a single one of them feels that downsizing your exhaust is the answer to better performance. You know, by the same reasoning, holding the exhaust in the engine longer should make more power, shouldn't it?

[Robyn]

There has been lottsa snake oil fixes for the 6.5 and nearly all of them are worthless wastes of time and $$$$$

The 6.5 has always been a problem child when it comes to keeping the temp in check in hot weather and when the rig is worked hard.

Every truck we have had here has to some extent been fussy in hot weather, even when new.

The best fix was to get the fan clutch working before the coolant was at 230 F and then the beast was OK.

[arveetek]

The 6.5 has always been a problem child when it comes to keeping the temp in check in hot weather and when the rig is worked hard.

Every truck we have had here has to some extent been fussy in hot weather, even when new.

With the dual thermostats, HO water pump, modified fan clutch, and all-aluminum radiator, I finally feel comfortable when towing and no longer have to keep my eyes glued on the temperature gauge. I still have to back off the throttle some on mountain passes, but now the engine stays pretty much a constant temperature under load: right in the middle of the gauge.

Casey

[Robyn]

Pretty much how it's done.

Why did GM release these trucks with such a sketchy cooling system ????

Even the New 6.5 rigs I have had were marginal in the hot weather...

[Yukon6.2]

Why did GM release these trucks with such a sketchy cooling system ????

Bean Counters R the Devil.

[Robyn]

YESSSSSSSSSSSSSSSS...The beanies saved GM a few $$$ but cost them millions of $$$

For very little more per unit cost the 6.5 could have been a great engine, but with a few strokes of the beanies pen the 6.5 was reduced to a very marginal piece at best.

So much could have been done differently and was not.

Poor castings
Poor crank
A real POS injection system.
A marginal cooling system

Had the 6.5 been built up using better iron, a deep skirted cross bolts block, heads with better materials and far better coolant flow and add a few more head bolts just for good measure...then toss in a top notch forged crank.

The electronic injection needed at least several more months of serious refinement before it was ready for prime time.

Ahhhh yesss.....

Could have been...GM's legacy.


Maybe VW was not all wrong in their approach to dealing with things.

[DmaxMaverick]

......Had the 6.5 been built up using better iron, a deep skirted cross bolts block, heads with better materials and far better coolant flow and add a few more head bolts just for good measure...then toss in a top notch forged crank.......

Ha! You just described what became the Duramax.

[Robyn]

Yup...pretty much.

Could have saved GM the second nasty black eye after the Olds oil burner debacle.

Ah well...the beanies know best it would seem.

[Robyn]

There were a few experimental engines made during the run up to the 6.5... even one with direct injection.

Obviously the beanies nixed them too.

[More Power]

With the dual thermostats, HO water pump, modified fan clutch, and all-aluminum radiator, I finally feel comfortable when towing and no longer have to keep my eyes glued on the temperature gauge. I still have to back off the throttle some on mountain passes, but now the engine stays pretty much a constant temperature under load: right in the middle of the gauge.

Casey

A better turbocharger is the final piece of the engine cooling puzzle.

All of the cooling system upgrades promoted here through the years did solve the engine temperature problems, but only a better turbo can reduce EGT (which indirectly affects ECT in a max power setting).

Try a Holset HX-35 (1994-98 Dodge Cummins app) for a step up from the GM-x series turbos or install a Holset HX-40 for a more dedicated heavy hauler.

[ronniejoe]

One must keep in mind the origins of the 6.5. The 6.2 L Diesel was designed to be an economy oriented offering, not the current beasts which are the product of renewed power wars between the big three. GM did learn its lessons from the Olds 350 Diesel. The 6.2 was designed as a Diesel from the ground up by the Detroit Diesel Allison Division. However, GM at that time did not believe that the economics of the automotive and light truck market would support the cost of typical medium/heavy duty Diesel engine technology. So, they tried to apply automotive gasoline engine design practices to Diesel engine design for automotive use. They largely succeeded with the 6.2 L NA engine. While it was not a powerhouse, by nearly all measures, it was very successful.

The year 1990 was an inflection point for the Diesel engine market in light trucks. This saw the introduction of the Cummins 5.9 L Turbo Diesel into the Dodge Ram pickup. Interestingly, Cummins offered the engine to GM first. (Interesting side story... I know some of the engineers at Cummins in Columbus, IN and one of the test operators who worked on their 5.9 L project. They built a late 80s 2500 GM truck with Cummins 5.9 L in it and took it to Detroit to give a demonstration to GM brass. GM turned them down cold. Next up? Dodge. They built a Dodge pickup and Chrysler was hooked. They didn't have a Diesel to compete with the GM 6.2 L or the Ford 6.9 L or 7.3 L IDI Diesels at the time.) Although the power offering was a meager by today's standards 160 hp, it was significantly higher than the 6.2 at 135 hp (18.5%). My uncle bought an early 1990 Dodge Cummins Diesel. I rode in that truck when it was new, just a few weeks after he got it and I said, "This changes everything. If this engine was in a good truck, it couldn't be beat."

Where GM screwed up is in not seeing where the market was going after the introduction of the Cummins in the light truck market. They tried to keep up by boring the 6.2 L to make the 6.5 L and adding a turbocharger. The problem is, they really screwed up the turbo match. The turbocharger is the biggest driver for the 6.5 L engine's overheating problems. It's simply too small on the exhaust side. Even though the early 6.5 L Turbo Diesels were competitive on advertised power, they couldn't deliver that power reliably over the long haul.

The reliability problems with the introduction of the DS4 pumps hurt badly as market share disappeared. The introduction of the electronically controlled turbo wastegate, while potentially a good idea, was also botched as the control system would dump boost right when the engine needed it most. Additionally, the blocks were not designed to handle the stresses associated with turbocharged operation and main web cracking became a problem.
These combined issues soured GM management on the engine (and Stanadyne, by the way) and the rest is history.

Ford initially tried to respond to the Cummins in the same way as GM by adding a turbocharger to their IDI 7.3 L Diesel. This was a short lived stopgap measure as they saw the future and developed the Powerstroke Diesel and introduced it in 1994 to compete directly with the Dodge Cummins. GM didn't wake up until it introduced the Duramax Diesel in 2001.

[ronniejoe]

Back to the dual thermostats...

The bypass restrictor that is available is a really bad idea as I said before. Ask yourself the question, "When the thermostats are closed, how does the coolant circulate through the engine?"

[Robyn]

Great info RJ

History has kept GM in the backseat for most of the diesel pickup era for sure.

It would certainly be interesting to fully understand why the powers at be made the lame decisions they made...

[arveetek]

I often remind folks who might look down on my 6.5L diesel, that my rig is currently 23 years old, and that the basic engine was designed in 1981! I, for one, think it's doing pretty good for running so strong at 340K miles, and on a basic design that is now 37 years old!!

Sounds like a turbo upgrade is in my future if I want to keep towing. For local trips, things are pretty good now. But our attempt at towing a 4,000lb camper to Yellowstone this summer didn't pan out (OEM radiator blew apart), and I had to keep an eye on EGT and ECT when pulling a mountain grade. I can definitely tell she did NOT like pulling those long, steep grades! We don't have anything like that here in SW Missouri.

Casey

[Kennedy]

I see Walt has a single stat that supposedly outflows the dual stats. How a conventional reverse flow even comes close to the flow area of a balanced sleeve is beyond me.

On the bright side I think we are past the rear head bypass BS that a certain vendor has at a Rendezvous a decade plus ago touting as the latest. I also hope we are past the 70% flow bias in the OE water pump BS, but I do see Leroy has a "balanced flow" water pump

[ronniejoe]

I see Walt has a single stat that supposedly outflows the dual stats.

I've posted these pictures before, but here goes again.









Look at the difference in size of the bypass flow passages. The single thermostat crossover thermostat was the "block off" type as seen here:



This stat closes off the bypass when it is fully opened. The valve adds blockage to the through-thermostat flow when opened, however. The dual stat housings did not use this type of thermostat for two reasons that I can see: 1) eliminate the blockage caused by the valve structure seen the photo (the valve would also need to be much larger to close off a larger bypass port, thereby increasing blockage) 2) use the same part number in both locations for the dual stat housing.

The bypass restrictor reduces the bypass flow area to significantly less than that for the single thermostat housing. This will significantly reduce the bypass flow and when the stats are closed, will cause the pump to operate at significantly higher back pressure than it was designed for. This is because flow through the pump is throttled by the restriction. This causes the impeller to churn the fluid because very little is leaving downstream. This causes an increase in the local temperature of the fluid and can lead to cavitation, which causes erosion on the impeller and pump housing degrading its efficiency. The pump is being damaged under these conditions.

One could, in theory have a single thermostat crossover that flows as well as or better than the factory dual thermostat crossover in bypass mode, but it is difficult to see how a single standard thermostat could ever flow as much as two thermostats in through-thermostat mode. Does he have some custom thermostat made out of unobtainium that provides double the flow?

I consider this the same as his many other difficult to swallow claims.