Bypass cooling for the 6.2/6.5

[damork]

I agree with not bypassing and had first hand experience with another fleet of GM engines - the 53 & 71 series 2 cycles. I worked across the middle east during the oil boom of the late 70's and early 80's and the 2 cycle Detroit Diesels were very common, we had several 4-53, 6V-53 and 8V-71 engines in our fleets.

When cooling became an issue our mechanics started pulling thermostats and rerouting coolant from the back of the heads. Just like what is mentioned here - the heat was not getting carried out of the engine as designed and made the problem worse. Coolant passages are designed to utilize the hardware in a certain way and if bypass was necessary it would have been done at the factory.

[moody]

Any chance the origanal post could be saved as a sticky on the 6.2 tech forum or made into an artical for the diesel page? Great work and pictures.

[More Power]

On a related note: The fourth image is of a 6.5 block that had a problem running the hill during our Pull-Off in 2002. You can see that the piston in cylinder #6 was damaged along with the cylinder. What is also visible is that #8 was undamaged.

Whether it was a competitive driver or just too much going on to keep track of, the engine temperature crossed 250 degrees and EGT went above 1500 during that run. Also, one of the other photos used here was of the very same rebuilt shortblock with new ceramic coated 18:1 pistons...

Jim

[ronniejoe]

I'm pretty sure what Grape is doing is pulling water out of the pump, piping it down the outside of the block and bringing it into the block in the center of each bank, probably through a freeze plug hole or other newly machined inlet port. Then, by opening up the transfer passage in the front of each deck surface, he can allow the coolant to flow from the center of each bank forward and rearward, then up through the heads and out at both ends. He's probably added a larger passage to pass coolant to the heads in between the center two cylinders on each side as well. This way he gets nearly parallel flow, rather than the series loop that the factory has. This approach has to be carefully metered to balance all the flows to avoid hot spots. If done properly, it will maintain more even temperature distribution throughout the enigne.

Just guessing.

[aloharovers]

So why doesn't the head gasket have holes in it to match up these coolant passages? (in blue)

[HammerWerf]

Aloha Rover,

After reading your post, I took a really close look at the picture of the gasket that MP highlighted the coolant passeges in green. They are hard to see, and very small, but there are holes that corrispond to the cleanout holes in the block and head.

MP indicates that these tiny holes are to allow air and steam to pass from the block to the head for removal from the block.

HammerWerf

[More Power]

HW, you are correct. And, those little holes are usually plugged with stuff not all that long after the engine is put into service.

Jim

[gsimpson]

I was reading the article and why would you make the holes in the head gasket so much smaller than the passages in the block and head?

Also wouldn't make the engine run cooler with increased head gasket passages?

Wouldn't you drill them out to match the ports in the block and heads?

[More Power]

I was reading the article and why would you make the holes in the head gasket so much smaller than the passages in the block and head?

Also wouldn't make the engine run cooler with increased head gasket passages?

Wouldn't you drill them out to match the ports in the block and heads?

There are a lot of engineering principles involved with coolant flow and heat transfer. The various holes in the head gaskets are sized to allow a prescribed amount of coolant flow. The size of the coolant passages in the head/block are the size they are for at least a couple of different reasons.... 1- Manufacturing ease and core cleanout. 2- To control coolant flow.

This is why the article was written.... Wannabe vendors just can't decide on their own to change coolant flow without some sort of dynamic testing on a fully instrumented engine to measure the effects of any change. The vendor data should also be published so it can be verified.