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Thread: Cooling Upgrades Techie Question

  1. #1
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    Default Cooling Upgrades Techie Question

    Good Day!

    Why are dual thermostats part of the cooling mods?

    If memory serves, the cooling upgrade GM introduced to our beloved 6.5TD in 97 (?) includes a higher-output water pump (85 (?) gpm to 130 gpm) & a new, dual thermostat housing. These components are fortunately available for retrofit from several top-quality DP advertisers.

    Again from memory, this upgrade increased flow through the block ~ 75%, & flow through the radiator ~ 9%. This makes sense, as some of the cylinders (6 & 8?) seem to fail from overheat before any others; it seems like increasing coolant flow through the block might stop this problem.

    My question comes up because if flow through the radiator is only increased ~ 9%, why do we need dual thermostats?

    TIA & Blessings!
    82 6.2NA K15 4X4 pickup, 4spd man w/ OD, 335K+ "In Rust We Trust" (parked)
    95 6.5TD 2500 4X4 pickup, Gear Vendors Aux. OD, > ¼ million miles - gone
    95 6.5TD 1500 4X4 3/4T Suburban, Kennedy exhaust, > ¼ million miles
    93 6.5TD 3500 4X4 1T crew cab LB pickup, 230k miles

  2. #2
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    Default

    IIRC, the higher GPM waterpump was to increase coolant flow through the block, to help eliminate "hot spots" in the heads and elsewhere where the coolant would start to boil. Increasing the flow across the surface of the interior block parts helps to transmit more heat to the coolant and out to the radiator.

    Why would flow only increase 9% through the radiator? Hmm, the outlet of the dual stat system didn't increase in size did it? Exactly.

    97 was the first year to be standard on all normal production 6.5's.

    It was on mid to late 96's as well.

  3. #3
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    Default

    Good Day!

    "Why would flow only increase 9% through the radiator? Hmm, the outlet of the dual stat system didn't increase in size did it? Exactly." Which makes me wonder all the more - why the dual 'stats?

    Blessings!
    (signature in previous post)

  4. #4
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    Maybe in case one fails?
    Or to allow a combo - 1 180 and 1 195?
    Or - obviously I don't know - but I went with option 2....
    OOps sold my "baby" - 96 K-2500 6.5TD - ~047,068mi, Isspro's Boost, Pyro, and Tranny temp; Heath Plate Remote mounted FSD; Amsoil Fluids and Air; Bilsteins, BD Down Pipe-Gutted CAT-& B-D'ized 3.5 Kennedy exhaust; '97 cooling upgrade; CAD upgrade; new IP at 34,700 under warranty; Homemade: Boost fooler, Hi/Lo idle, OPS relay, TCC Lockup ( TFT), Glow extender for AC60's, & "GMC H..'s" 6 position Shift modifier .

  5. #5
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    Quote Originally Posted by moondoggie
    Good Day!

    "Why would flow only increase 9% through the radiator? Hmm, the outlet of the dual stat system didn't increase in size did it? Exactly." Which makes me wonder all the more - why the dual 'stats?

    Blessings!
    (signature in previous post)
    The thermostat has a flow area considerably less, and restriction considerably more, than the outlet, hose, and radiator core. Duals closes the gap between them, and also allows more of a progressive and responsive engagement. Redundancy would be a bonus, but not by design.
    1985 Blazer 6.2
    2001 GMC 2500HD D/A
    dmaxmaverick@thedieselpage.com

  6. #6
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    Good Day!

    Thanks everyone - just what I had hoped for. Further clarification of course gratefully accepted.

    Blessings!
    (signature in previous post)

  7. #7
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    While I lived in Washingotn, I had the oppurtunity to visit Bill Heath. I was waiting for him to get off the phone so, I tooled around the shop. There was an engine on the stand with the dual thermostat crossover. I had mine off (I have a single crossover, the newer single thermostat style) at one time and noticed that there is a restrictor disc built into the the crossover, where the coolant enters the recirc path back to the water pump. We'll, the dual stat didn't have one.

    They added another stat with reduces restriction and increases flow through the radiator, but removed the restrictor disc, which reduced the restriction for the recirculation path, increasing recirc flow, but reducing the radiator flow what it would be with the disc and dual thermostats, Hence, only 9%.

    Now, if I can only get stationed in Wisconsin.....

  8. #8
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    Good Day!

    That REALLY helps - thanks.

    Blessings!
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  9. #9
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    The difference in coolant flow for the block and the radiator is due to the volume difference and flow paths.

    The radiator flow cross-section is far larger than the block inlets/outlets, so the coolant flows more slowly. This not a bad thing...

  10. #10
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    As was mentioned earlier, "to eliminate hot spots"
    The factory heads have some areas that the coolant can stagnate in and the extra flow will cause more turbulence and result in the mixing of cooler water being routed into these "Dead zones"
    The bottom line is less head problems such as cracking.
    My personal opinion is that GM did this as a stop gap measure to redesigning the heads.
    Retooling is costly any way you cut it and when an engine design is slated for termination (production end) they are not going to spend the $$$
    The addition of the dual stats and different pump was a cheap fix and it seems to have helped for sure.
    It would be interesting to see if the heads coming from Navistar and also the ones from the after market (clear water) are the same inside as far as flow asd the GM heads or if the flow issue was fixed as well as the thickness of the head in the crack prone areas.

    Just some thoughts

    Robyn
    Last edited by Robyn; 10-08-2006 at 08:13. Reason: spelling
    (1) 1995 Suburban 2500 4x4
    (1) 1997 Astro
    (1) 2005 Suburban (Papa Smurf)
    THIS IS BOW TIE COUNTRY

  11. #11
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    Default Water Wetter?

    Any opinions of use of "Water Wetter" or Dawn dish soap?
    OOps sold my "baby" - 96 K-2500 6.5TD - ~047,068mi, Isspro's Boost, Pyro, and Tranny temp; Heath Plate Remote mounted FSD; Amsoil Fluids and Air; Bilsteins, BD Down Pipe-Gutted CAT-& B-D'ized 3.5 Kennedy exhaust; '97 cooling upgrade; CAD upgrade; new IP at 34,700 under warranty; Homemade: Boost fooler, Hi/Lo idle, OPS relay, TCC Lockup ( TFT), Glow extender for AC60's, & "GMC H..'s" 6 position Shift modifier .

  12. #12
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    Quote Originally Posted by MTTwister
    Any opinions of use of "Water Wetter" or Dawn dish soap?
    I used Water Wetter, but didn't notice any difference. The principles it's based on are sound.

    It will leak out unless your system is absolutely tight (someone here told me that and I subsequently found that out.)

    If i had to make the decision again, I wouldnt bother.

  13. #13
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    Quote Originally Posted by robyn
    As was mentioned earlier, "to eliminate hot spots"
    The factory heads have some areas that the coolant can stagnate in and the extra flow will cause more turbulence and result in the mixing of cooler water being routed into these "Dead zones"
    The bottom line is less head problems such as cracking.
    My personal opinion is that GM did this as a stop gap measure to redesigning the heads.
    Retooling is costly any way you cut it and when an engine design is slated for termination (production end) they are not going to spend the $$$
    The addition of the dual stats and different pump was a cheap fix and it seems to have helped for sure.
    It would be interesting to see if the heads coming from Navistar and also the ones from the after market (clear water) are the same inside as far as flow asd the GM heads or if the flow issue was fixed as well as the thickness of the head in the crack prone areas.

    Just some thoughts

    Robyn
    Now, Robyn, youreally know the answer don't you? When I was an oil peddler in the late 60'/early 70's, Detroit Diesel 6-71's with the 65 injectors (rated at 318 HP) had overheating problems. GM's solution? Bigger cooling passages? Higher capacity water pump and radiator?

    Three guesses:




    Nope, wrong!





    Wrong again!




    Solution: Advertise it as, "The Cool One"! (I came to this conclusion in collaboration with one of my customers who was an OEM DD dealer - we examined things pretty much in detail...)

  14. #14
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    Good Day!

    rustyk: Could you interpret your last post for me? I have no idea what you're talking about.

    Thanks & Blessings!
    (signature in previous post)

  15. #15
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    Sure, you mentioned the GM instituting the dual thermostat/higher cap pump as a stop-gap measure.

    Stop-gap measures tend to be signature solutions for GM.

    I agree with you that they probably tried it to avoid a redesign/retooling of the heads. The problems with the 6-71/318 (which go back to the early '70s) I mentioned to show a trend...

    In that case, they basically did nothing except refer the issue to the marketing department for a solution.

  16. #16
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    A thought ... only a thought - I can see wisdom in running the high out water pump to help cool the heads, but I too am a little curious about the dual t-stat. In the past, I have oft been known to modify water pumps on some engines, gassers to be more precise, by removing half the blades to reduce cavitation & drag on the engine, = more available power. I have done a number with only running slightly warmer at idle. What's this got to do with a dual t-stat diesel setup? Nothing. But, wouldnt shoving the coolant through the radiator faster allow less time for cooling? I have always been of the mindset that letting the coolant move slower through the radiator allows more time for the temp to drop before returning to the engine. Ever remove a t-stat from your engine & find it actually runs hotter than with?

    Tim

  17. #17
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    Moving water through too fast can cause an overheat issue in hot weather as the radiator does not have time to dissipate the heat.
    The dual stats allow each side of the engine to open the stat when the temp is optimum.

    To answer another post.
    The 318 was actually the small horse power 8V71 the larger ones went up to
    475 in the 8V92 silver
    The 6V71'a were available in Hp's down to around 265 in the coach applications and up to 360 in the turboed version. I had a city bus once that I converted to a motor home, it had a small hp 6V 71.
    I got rid of that unit and bought a big "Hound" and converted it.
    GM has always been good about sugar coating things and side stepping issues untill the time that they could phase the design out and start into some other debacle.
    Funny
    They got it right with the small block's (mouse motor) 265-350
    we wont mention the 400 SB
    And the MK IV 396-454 (Rat Motor)
    Great designs that lasted decades and served well with minimal troubles over the long haul.
    Starting with the 5.7 Olds diesel and on to present they just cant seem to get it together. Once they get it figued out they scrap the design and go build another mess to sort out.
    We won't even mention the 4 cyl vega.
    I think all the big manufactures have placed all controls now on design with the bean counters and none with engineering.
    Ford has had their share of crap too as has MOPAR.
    One thing the factories dont do any longer is "road test" they dont give the prototype to "BUBBA" and have him beat it to death on the test track as in the past. Most all testing is done in a computer program. WRONG answer. It takes a crazy to beat the stuff to death to really find issues that will come into play when you hand it over to the general public..
    If the factory had taken only a small number of rigs and set them up with folks to beat them every day under the worst possible conditions for a year prior to production runs most of the stuff you and I have seen could have been fixed.
    The issues with the PMD and IP's
    overheating
    Cracked heads, Blocks, cranks
    All these little gremlins would have come to light and could have been addressed prior to ever building a truck for the general public.
    The overall picture in the motoring publics eye would have been a great one instead of how it turned out.
    I rest my case
    Robyn
    (1) 1995 Suburban 2500 4x4
    (1) 1997 Astro
    (1) 2005 Suburban (Papa Smurf)
    THIS IS BOW TIE COUNTRY

  18. #18
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    GM introduced a higher capacity water pump primarily to increase flow through the cylinder heads, which was intended to sweep away the thin vapor boundary layer formed on the hottest portions of the heads - thus allowing cyl head heat to be transferred to the coolant, which reduces the incidence of head cracking.

    Dual t-stats add redundancy and increase maximum flow capacity. Flow through the radiator is not necessarily increased by the same amount as the increase in water pump flow rate. This is because the earlier 87-gpm systems used a blocking bypass thermostat, that forced all coolant through the radiator when the t-stat was fully open. The 97+ t-stats do not block water pump bypass coolant flow.

    Jim

  19. #19
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    Good Day!

    "What's this got to do with a dual t-stat diesel setup? Nothing. But, wouldnt shoving the coolant through the radiator faster allow less time for cooling? I have always been of the mindset that letting the coolant move slower through the radiator allows more time for the temp to drop before returning to the engine."

    (From my initial post) "Again from memory, this upgrade increased flow through the block ~ 75%, & flow through the radiator ~ 9%." If this is so, they're NOT increasing flow through the radiator much at all, but LOTS through the block, reasons being explained (THANK YOU!) in previous posts by others, which is why I started this topic in the 1st place. :

    Blessings!
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  20. #20
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    Quote Originally Posted by robyn
    Moving water through too fast can cause an overheat issue in hot weather as the radiator does not have time to dissipate the heat.
    The dual stats allow each side of the engine to open the stat when the temp is optimum.
    Be careful, it is not true that increasing the flow speed (or flow rate) causes overheat issues. This is contrary to the laws of thermodynamnics. The faster the flow rate, the more heat that can be dissipated.

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