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Thread: Bypass cooling for the 6.2/6.5

  1. #21
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    I wouldn't modify (enlarge) the small holes in the head gaskets we're talking about there. Larger holes could alter coolant flow patterns through the heads in unexpected ways.

    Incidentally, any air pockets that remain in an engine will slowly be absorbed by the water/coolant mixture. Over a few days or a couple weeks, the air will disappear. This assumes the air pocket is below the uppermost coolant level in the cooling system.

    Jim

  2. #22
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    i make the holes bigger but that's cause i'm moving water up, not back-up-then forward.

  3. #23
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    I think that removing water from the heads is a big mistake. There are others that disagree.

    this will do NOTHING to help prevent a cracked block. The cracks form at the bearing journal, which is far way from the cooling jackets.

    the blocks aint cracking because they are getting hot.

    Tim
    Last edited by More Power; 11-24-2008 at 21:37.
    Ford Owner.


    Music by Andrew Lloyd Weber. Lyrics by Andrew Dice Clay

  4. #24
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    "Bypass cooling" is, to me, an oxymoron. GM engineers might not be the brightest lights in the chandelier, but I'd go with their cooling scheme anyway.
    '94 Barth 28' Breakaway M/H ("StaRV II") diesel pusher: Spartan chassis, aluminum birdcage construction. Peninsular/AMG 6.5L TD (230HP), 18:1, Phazer, non-wastgated turbo, hi-pop injectors, 4L80E (Sun Coast TC & rebuild, M-H Pan), Dana 80 (M-H Cover), Fluidampr, EGT, trans temp, boost gage. Honda EV-4010 gaso genset, furnace, roof air, stove, microwave/convection, 2-dr. 3-way reefer. KVH R5SL Satellite. Cruises 2, sleeps 4, carries 6, and parties 8 (parties 12 - tested).

    Stand-ins are an '02 Cadillac Escalade AWD 6.0L and an '06 Toyota Sienna Limited.

  5. #25
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    I have done this particular modification well over 100k miles ago with only positive results. I did not do this because I felt the large holes could pass water. I saw that besides the large passage at the rear of the block, only the small holes between the cylinders pass water to the heads. The water is coolest in the block closest to the water pump inlets. The water is hottest when it passes through the heads and exits at the thermostat crossover. The small holes helps to balance the temperature in the heads by using the coolest water in the block with the hotter water in the heads.

    It was explained to me that the larger passage in the back flows more of the hot water, which like all hot things is trying to expand. That limits flow between the head and block at the smaller holes. Reducing flow of the hotter water allows more of the cooler water to pass from the block upwards to the heads.

    Before installing this setup I was seeing temps on the dash gauge of better than 210 on a hill coming into Santa Fe, NM, an elevation of 7,000, with outside temps of around 90. I also had a gauge installed on the passenger head at the rear and temps there were showing as high as 235. After making the change I could keep temps at 210 on the dash gauge and around 220 on the other one. Every place where I towed and saw higher temps, I now have lower temps and less differential between the front and back of the engine.

    It seems that most of those opposed to this idea are doing so based on their theories. When they have some real experience with the idea and can show it will negatively affect engine life, I may consider their experiences. Right now I can only go with what I have observed myself and it doesn't seem to conform to the theories and speculation.

    I spent around $200 doing the setup using braided lines and having fittings welded to the thermostat crossover. I have an extra crossover so that I could have put things back to stock if I felt it wasn't working. Haven't seen a need to change so far.
    94 K1500 6.5 TD<BR>2K Honda CR250

  6. #26
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    GM increased the water pump flow rate from 87-gpm to 130-gpm primarily to increase coolant flow through the heads in an effort to reduce the incidence of cylinder head cracking. That's not a theory. By-pass cooling reduces coolant flow through the length of the heads. That's not a theory.

    There are a couple of different vendors who produce these kits. I spoke to one of them a couple of years ago about by-pass cooling. I offered to travel to them, at my own expense, to witness an instrumented test using at least three thermocouples on one head. I was not invited. If I sold and believed in these kits, I would welcome/encourage an opportunity to prove their worth.

    I would like to see the cyl head temperature between the valves on each of the end and center cylinders during a sustained full load (long grade, heavy trailer, full pedal or 1250 degrees EGT). If the temperature(s) could be shown to be lower at each thermocouple with by-pass cooling, I'd write a story and advertise that product at no cost to the vendor. We are, after all, here to help 6.5 owners.

    Jim

  7. #27
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    Question Marine application for bypass, or?

    Jim, I've been wondering if those openings at back of heads are there for marine applications where the body of water is the cooling medium, or?
    99 GMC SUB, 2500, 4x4, 6.5 TD (F) #H32 enhanced blk, Phaser timing set, B&D IC, 3" ATS exh, K&N w/prefilter, 4WD NVG 246, 4L80E kevlar Transgo off road/tow mods/B&M supercooler, 14 FF MagTec w/locker 3.42:1, 9.25" IFS frt/diff 3.42:1 w/ARB locker, AutoMeter Boost & pre-turbo pyro meter, 12,000 lb hydro winch, Warn classic bumper w/brushguard & diesel scoop, Max E-torq Stage 3, hi pop inj, oil bypass sys, on board air comp for front ARB locker & tire inflation, DynaView driving/auto-cornering lts, DZ nerfs, A/T 285/75/16 SilentArmor 3750 lb rated on 3750 lb rated Alcoa, 3 IP drivers 2 r spares.

  8. #28
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    The coolant crossover uses the openings at the front of each head. If you swapped the heads right for left on the block, the opposite end of each head would now be at the front. So, the heads contain openings at both ends to allow them to be used on either bank.

    The single most important coolant temperature is that temperature within the cylinder heads. Bypassed coolant isn't picking up heat in the heads. So, of course, the coolant will show a lower temperature.

    Jim

  9. #29
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    I do have the higher output water pump and dual thermostat on my 94 as well as the Kennedy fan clutch and Dmax fan. My temps are more under control than when the rest of the engine was stock and much better than after doing some mods.

    My observation was that the output from the water pump is a larger hole than the output from the crossover. The flow from the crossover and bypass lines, in my opinion, is not more than the flow from the water pump. The crossover itself is a restriction to flow and as I stated earlier, the hotter water in the front cylinders of the heads can reduce transfer of cooler water from the block into the hotter end of the head.

    I'm not trying to get into a big argument with anyone, but my results have been positive and I have been running my truck this way for over 100k miles. I only have a 1/2 ton, so I have not had loads as extreme as some might, but I do have a 5th wheel that has a lot of wind resistance and do run up some steep hills in thin air with high outside temps. I try and avoid 1250* egt's and lift when I get close. My destination will still be there a few minutes later.

    The only way a test would really indicate something is do run it with the bypass and again without it. It would be interesting to see if testing could show a benefit or not, but I do feel that long term results show something as well.
    94 K1500 6.5 TD<BR>2K Honda CR250

  10. #30
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    I'll say it again.....

    Bypassed coolant isn't picking up heat in the heads. So, of course, the coolant will show a lower temperature.

  11. #31
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    Can we have a BIG "AMEN"?!

    Sometimes I wonder where these Bright Ideas come from. The only useful bypass (which most engines have) is to route coolant to the heater core to provide cabin heat as quickly as possible, until the 'stat opens...
    '94 Barth 28' Breakaway M/H ("StaRV II") diesel pusher: Spartan chassis, aluminum birdcage construction. Peninsular/AMG 6.5L TD (230HP), 18:1, Phazer, non-wastgated turbo, hi-pop injectors, 4L80E (Sun Coast TC & rebuild, M-H Pan), Dana 80 (M-H Cover), Fluidampr, EGT, trans temp, boost gage. Honda EV-4010 gaso genset, furnace, roof air, stove, microwave/convection, 2-dr. 3-way reefer. KVH R5SL Satellite. Cruises 2, sleeps 4, carries 6, and parties 8 (parties 12 - tested).

    Stand-ins are an '02 Cadillac Escalade AWD 6.0L and an '06 Toyota Sienna Limited.

  12. #32
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    I don't see where you can prove that the heat is not transferring to the water. If hotter water is being used to "cool" the heads, the temperature of the head will be higher. Increasing the flow of hot water through the head isn't beneficial.

    If it's such a bad idea I would expect to have seen a problem with it by now. The only thing I have seen is lower overall temps and less variance between the temps at the rear of the head versus the front. The temps at the rear of the head where water is just entering the head is lower under tow conditions. It is not because it hasn't picked up heat from the head, because it hasn't passed through much of the head yet.

    Again, running the same hills with the same outside temps and the same load has shown lower temps and quicker return to normal temps. Over 100k miles of testing hasn't shown a problem.
    94 K1500 6.5 TD<BR>2K Honda CR250

  13. #33
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    The bypassed coolant should be traveling through the cylinder heads, but in your case, it's not. So, only a fraction of what should be traveling through the heads actually is.

    By bypassing, the bypassed coolant will move faster (less resistance when compared to traveling through the heads), which produces an artificial lower temp where you're measuring it at the back of the heads.

    If you had a thermocouple located at the mid-point inside the cylinder head, it would show a higher than normal temperature when using a bypass strategy. This is exactly where the GM engineers wanted to reduce temperatures. This is why they upgraded to a 130-gpm water pump.

    In your case, perhaps you haven't run the engine at a high enough load and subsequent ECT/EGT temperature level to cause cylinder head problems. Your guess is as good as mine. I know a guy who reported 450,000 miles on his original FSD module too.

    I'd love to be invited to participate in a bypass cooling test (with/without)where an instrumented 6.5 head was used. We'd use a 10K trailer, a 6% grade and full pedal for a minimum of 1 mile - longer the better. Then compare with/without bypass cooling. If the bypass strategy could show a lower temperature at mid head, I'd write an article singing its praises and I'd promote whatever vendor sells it - at no cost... Till such a time, I'm going with what the GM 6.5 cooling system engineers say about what works best for the 6.5... More flow t h r o u g h the heads - to reduce the incidence of cylinder head cracking...

    The Diesel Page doesn't sell any parts for your engine. There is no financial incentive for me to promote any part (or suggest not using a part). We just want to help folks be successful 6.5 owners.

    Jim

  14. #34

    Default 130 gpm water pump?

    I guess this is a little of subject, But does anyone no if the 130 gpm water pump will bolt directly to a 1994 truck?
    Toby

    1994 Chevy K2500
    6.5L Turbo Diesel, Stock

  15. #35
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    The 1996 and earlier factory 6.5 water pumps were rated at 87-gpm, which were designed to operate with a single thermostat.

    The uprated 1997/98 130-gpm water pump is a direct bolt-on, and your existing fan-clutch will bolt on. We recommend using the twin thermostat setup as well. Several vendors sell the complete kit using all genuine GM parts.

    The uprated water pump is also available in the 1999/00 style, which contains an integral water pump pulley that includes a threaded fitting for a screw-on style fan-clutch. Whether 1997/98 or 1999/00 style, each produce 130-gpm at 3000 engine rpm.

    These are not "heavy-duty" water pumps. They are "High-Output" water pumps. Only the 1997/98 style water pump is marked "HO".

    Jim

  16. #36
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    wonder why the australians are so fond of this mod ? something about steam pockets, steam bubbles and cavitating water pumps,. so more flow works better,. they run their stuff in the desert,. and when the pump is pumping water around the block thru the heads and also thru the bypass lines, if it comes to a closed thermostat, then the water gets sent around again, till it is hot enough to open the t-stat,. the theories mentioned here seem to be based on the water heading straight back into the rad,.
    australians also drill the fire deck in the spots needed to increase the flow up thru the head,.
    "soak" time is not the best way to remove heat, "flow' works better,.
    JMHO,

    nick
    1999 chev suburban C2500
    300,000 mi

  17. #37
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    Quote Originally Posted by phantom 309 View Post
    wonder why the australians are so fond of this mod ? something about steam pockets, steam bubbles and cavitating water pumps,. so more flow works better,. they run their stuff in the desert,. and when the pump is pumping water around the block thru the heads and also thru the bypass lines, if it comes to a closed thermostat, then the water gets sent around again, till it is hot enough to open the t-stat,. the theories mentioned here seem to be based on the water heading straight back into the rad,.
    australians also drill the fire deck in the spots needed to increase the flow up thru the head,.
    "soak" time is not the best way to remove heat, "flow' works better,.
    JMHO,

    nick
    placebo effect.... who knows? Hot is hot, boiling is boiling, doesn't matter whether you're crossing the Outback or pulling the Grapevine out of LA at max GCVW in the middle of August. HMMWVs don't use bp cooling in the deep sand and 130 degree heat of the Iraqi desert.

    There are lots of theories about engine cooling, but not a lot of verifiable data collection out there - except by the GM 6.5 cooling system engineers who wanted dual t-stats used with their HO wp.

    Generally, the biggest proponents of bp cooling are vendors. I don't sell any part you can bolt onto your truck. I have no financial stake in whether a product helps or not. In fact, I've turned away vendors and their advertising who had crappy products or had ads that were over-the-top unprovable BS.

    I would hope that vehicle owner/proponents of bp cooling would be just as diligent in asking the vendors for hard verfiable data and photos of the testing equipment, and not just take their word for it that they tested it. Those vendors have a stake in selling you hardware.

    Through the years I've tested quite a few aftermarket products that were advertised to improve one thing or another. Some did, and I could usually prove it using data collection (i.e. performance products, using dynos, elapsed times). For those tests, I always included photos of the testing equipment and included pics of the truck on the hill or the dyno (plus indicated when & where it was dyno'ed so others could verify what I said).

    I've made the offer before.... Any vendor who will instrument a cylinder head using three calibrated thermocouples (end, center, end) to measure coolant temperature and can prove to me that bypass cooling lowers overall engine temperature or otherwise improves cooling, I'll write a story about it and give that vendor a free year of banner advertising. I'll travel anywhere in the continental US at my own expense to witness the data collection. Of course, and to be fair, if he's blowing smoke or the stuff doesn't work, you'll hear about that as well. My purpose for creating this web site 14+ years ago was to help owners improve GM diesel reliability, performance and ownership satisfaction. Still is.....

  18. #38
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    I'm sure I've posted this before, but I don't feel like digging through the posts to find it. So.....

    Heat is a product of consumed energy, and can be measured absolutely by many scales (BTU, KW, Calories, etc.). During operation, an engine consumes fuel and produces heat. That heat is present, regardless of the methods of removing it. It must be removed. In most all motor vehicle engines, this is done with a liquid-air heat exchange. Before the heat can be removed from the engine, it must first be transfered to the coolant, then moved to the liquid-air heat exchanger (the radiator). Any successful method of a more efficient heat removal will (all else being equal) indicate the additional heat being removed. There are several vendors selling a bypass cooling kit, as well as available published instructions. Each I've seen has claimed immediate cooling results, by an indicated engine coolant temperature decrease. Problem is, if the cooling method were in fact more efficient, the result would indicate the exact opposite: HIGHER indicated coolant temperature. If the method was actually removing additional heat, it would be indicated by an ECT increase, not a decrease. There should also be a more active thermostat and fan clutch with an increase of coolant temperature. A decrease in indicated ECT is evidence of LESS heat actually being removed from the engine.

    If your 6.5 is overheating, it needs to be fixed. Not bypassed.
    1985 Blazer 6.2
    2001 GMC 2500HD D/A
    dmaxmaverick@thedieselpage.com

  19. #39
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    http://www.4wdaction.com.au/forum/sh...ad.php?t=23850

    interesting read for the first few pages,.pay attention to 'LES ADDISON'
    he says the bypass cooling is not really that, but they are air bleeds to help release the bubbles caused by the sonic vibrations,. large diesels have the same sort of technology,.it stops cavitation at the water pump,.
    Interesting to see his modified waterpump,.
    shame that some of the pics aren't available,.

    Nick
    1999 chev suburban C2500
    300,000 mi

  20. #40
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    Default bypass cooling

    Hey guys, since I am reading this for the first time I have to say how interesting it is since I was just thinking after repairing my 6.2 head gaskets that I should run a line from the back of the head to the crossover. Obviously I won't do that now as I can see that this will cause more problems than it will solve! I didn't know there was any discussion about it or products for that matter, I just thought I would try it.

    HOWEVER if flow is the only true solution please advise me about running that same line but instead, from the pressure side of the water pump to the back of the head, in an effort to "add lower temp water flow" to the back of the head rather than removing the hotter water flow from that spot with a bypass? is there a fundamental flaw in this idea.

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