2 Thermostat Housings 1 Engine

[emmott]

At least with the redesigned water pump (251603), left/right coolant flows are 50/50 balanced.

But a pump redesign won't change a front/back flow imbalance. At least I think that's why the back runs hotter and #8 is the typical fail cylinder (with #7 as a close second). I see little indication the coolant passages in the block are restricted up front to encourage balanced flow. Water takes the path of least resistance and circulates more through the front because the inlet is at the front (the pump), and the outlet is also at the front (the thermostat housing).

I have 3 ideas to solve this:

1. Why is the cab heater hose coming from the font? Can we move it to the back? The heads have coolant outlets at both ends. These trucks don't have a cab heater control valve so the flow is already continuous. One could: Remove the cab heater hose from the thermostat housing and cap the hole in the housing; Remove the blind flanges from the heads in the back of the engine; Tee off a hose from the left and right head and Y them back together before the cab heater. This would encourage more circulation through the back of the engine. You would need to tee from both the left and right head to ensure you don't create a left/right flow imbalance.
2. What if the thermostat housing was relocated to the back of the engine? There would be hose re-routing and a FFM relocation, but you'd get more coolant circulation from front to back and improve temperatures at the rear of the engine.
3. You could run a front thermostat housing AND a back thermostat housing for completely temperature balanced circulation. (assuming you have the same # of thermostats font and back and they are all the same temp threshold). You'd need T and Y fittings and extra hose. Not sure if a thermostat housing from any year would fit between the firewall and the intake manifold. This certainly wouldn't work with a centremount turbo. And it probably is way overkill. But overkill = fun.

What are your thoughts on this? Has anyone tried it? If not I may do some experimentation and post results with my temp probe.

 

[schiker]

It’s been tried. # 8 gets some temp increase from the exhaust crossover design.

The spin on water pump fixes the problem. Not only is it better balanced it’s higher flow. More flow mixes the water in head better and flushes away hot spots.

 

[Will L.]

Welcome Emmott.
Gm did a ton of methods back when it was a new issue in the 90’s. The solution has been determined, and there are things you can do to help more depending how much you hot rod/ work the engine and depending on what rig you have it in.
Hummers/ hmmwv are worse off than pickups,but HD trucks do better than them- larger more vertical radiator/ cooling stack.

Fan and fanclutch is important. So is thermostat(s) and cross over. Also which coolant and additives help.
Radiator choices and coating options you can shed mega heat. Other things inside engine, which turbo and exhaust have big impact too.


Tell us a out you rig(s) and what exactly your running in them and we can help more.

 

[FellowTraveler]

On my 99 425 Burb dual HVAC the coolant is always flowing through the heater cores I suspect because this adds to the efficiency of the engine cooling system.

Best luck I had w/cooling system was converting to EVANS, tired drilled thermostats along with bypassing the bypass and , restricting the bypass while using a weather front on the grill in colder weather.

 

[schiker]

You can google heath's balanced flow kit to see some of the early attempts at adding flow to the rear of the head.

I think adding hoses at the rear blocked off ports somehow isn't increasing swirl over the head's hot spot(s). It might increase flow somehow at the rear but it doesn't mix and "turbulate" as well and flow over the head's lower surface (where heat is) taking a different passage out or in the rear block off port vs just the newer balanced water pump and increasing flow in OE directions. I think this is documented in more even temps measured in a few places in each head written up in a MaxTorque article on the balanced flow new water pump. Probably can also find it on here and or other forums.

Look at Leroy's water pump bypass restrictor for the double thermostat crossover.

I have always liked the idea of maybe adding "some more radiator" to the heater loop as it might cool the lower radiator hose more. With a clean radiator and good fan clutch most all have enough cooling with new water pump.

Some more of the straight forward approaches are: look into a better radiator with thermal dispersant on it like Twistedsteel offers. Or his fan clutch setup. Or AKdiesel's and others electro viscous fan lock-up mods.

Saying what Will did a bit different it's best to use a systematic approach and make sure mods complement each other.

 

[emmott]

Thanks guys. I added my build signature line. I already have the balanced screw pump and a brand new rad and flushed system. I'll look at the dispersant and maxtorque info, wasn't aware of those!

I saw Leroy's dual thermostat bypass restrictor, but plan to use a single T-Stat housing instead. Heath's cooling research recommended the single over the a dual with restrictor because even with a restrictor the dual can never 100% block the bypass. The single should encourage more pressure at full flow. I can't find the original link but I saved the PDF. Either option would suffice.

The screw on pump, rad maintenance, and dmax fan is probably enough for any 6.5 build. I just wasn't sure how the flow through the back half of the engine was being balanced, aside increasing flow across the board with a HO pump approach. I may try the first idea just to see what happens, easy to revert back to OEM routing. I like to tinker.

 

[Will L.]

Heath quit selling the rear head kits when he learned of the damage incurred from them. They mess with flow through the head and increase head cracks, as well as messing with moving the dead spot from cylinder 8 to cylinder 6 in the block.

Messing with flow system is fine and dandy providing you dont care about ruining that block and headset. Once you go through several hundred, your starting to catch up to what’s already been done.

On the single stat- make sure it is one with full block off of return to pump when stat is open.

Constantly feeding through a heatercore to help shed heat is simply making the radiator slightly larger. The thermal dispersant TSP does is good for roughly 1/3 increase in btu shed.

The Evans is something a few folks here found success with, but I am 100 opposed to it if you keep a heatercore. I know 2 people that suffered severe burns from it. Not burn. Like hot water at 250f burn. It is flammable and just like all oil products when a small leak occurs it mists out and that increases flammability and lowers flash point dramatically. So instead of the front passenger getting first degree burns on legs/feet, it becomes fuel spraying on people and lighting them on fire.

If you remove the heater core then the only risk is when the engine does get to 220 or above, the cylinders of #7 and #8 still colapse onto the rings because that is simply the clearances are that tight and the metal expands “X” amount at “Y” temperature. I suppose you could compensate for this some during a rebuild by over honing the cylinders and opening up ring gap, but you give up life of compression before blow by begins.

There also are some folks that don’t buy into the balanced flow at all and still run the 4 bolt HO pumps. Chris of TSP infact has the hmmwv fanclutch on the 4 bolt which is instant 100% lockup so the fan gets 15% speed all the time and the hmmwv fanclutch is rebuildable quite easily and affordably- gettin a used one of ebay is the trick there.
(I am at beginning stages of adapting hmmwv fanclutch to spin on pump. Another hummer owner is working on it too).
And it just like AKDiesel Drivers use of the dmax van clutch has the adjustability of coming on whenever you want by temp, and you can have manual override. Also you can tie it to a trinary switch of the a/c so the fan can kick on to cool the condenser- like any other modern rig.

 

[emmott]

I wasn't aware Heath had a product like that then discontinued them. Just read your 2017 post about it, cutting heads and watching the flows. The test results and GM voiding warranties if they found rear head cooling kits installed, makes it pretty clear you don't want to touch the back end. Thanks for the writeup!

I would not try evans if it's a safety risk. Definitely will look into thermal dispersant.

Do you know if 12551519 is full block off of return?

 

[Will L.]

Yes I believe it is.

 

[FellowTraveler]

Will! There is a fire risk with all glycol based engine coolant's on the market given the right opportunity to ignite with FORD, GM & BMW recalling many hundreds of thousands of vehicles that are at risk of coolant catching on fire resulting in vehicle loss. Fact is engine coolant fires are lumped in with the top 5 causes for vehicles fires globally.

While EVANS does not have a lions share of the engine coolant market fires attributed to their product are few and far between.

 

[Twisted Steel Performance]

And their IS a high flow 4 bolt pump as well....

 

[ak diesel driver]

I'm wondering if you'd mess up the balanced flow by using the bypass style thermostat?

 

[Will L.]

I'm wondering if you'd mess up the balanced flow by using the bypass style thermostat?

Yes and no. The balanced flow is still not exactly 50/50. It is more like 52/48 with 3/8 restrictor. Using the block off made it flip flop to more flow on passenger side than driver but nearly same percentage iirc.

Remember when AC Delco did the first pumps, it had the restrictor plate style fitting until that company that had the patent went out of business because of the AM General/GM lawsuit about the serpentine belt pump issues. The Dad that owned it died and the family refused to let GM use the patent.
When Working at the dealership, there was a description of how some owners ‘may’ have done an at home mod restrictor that we were NOT to remove if present and that it did NOT void the warranty of engine and trans like the rear rear head hose kits did. Basically they were telling us how to make the restrictor to solve issues but they couldn’t outright say it But the 3/4” hole was simply to big and reduced to 3/8 was the closest fix. The original fitting had a swirling cut to it and was actually smaller than 3/8, but the swirl cut made the coolant flow more laminar and stopped pitting from aeration. And that smaller hole got it to 51/49 roughly. Right as I left GM removed the info showing the original fitting and the how to imitation instructions.

Doing the block off stat though does create more pitting on the impeller blade, unless you use water wetter. The water wetter improves surface tension and makes it almost nothing. We played with enlarged bleed hole thats drilled in thermostat for trying to hit exact balance, but saw no thermal benefits, so let it go. The extra water getting cooled off negates the tiny shortened lifespan of the waterpump. Quality of coolant and using distilled water has way bigger impact on pump life from the small amount of pitting.

I would rather more coolant to the passenger side anyways if slightly off. #8 traps more heat then #7 by simple placement. Thats why it fails more often even after gm did the last block update in 99.