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Bad idea, and right on par with the bypass method. Increasing flow at the rear of the head will decrease coolant flow upstream. The dual stat and HO water pump upgrade is about as good as it gets. Assuming the rest of the system is healthy (radiator, stats, jackets, etc.).Quote:
Originally Posted by tomtaylor
So you are saying that any flow diverted will have will have a neg effect because the current design is as good as it gets without going to the HO pump and dual stats. correct?
Do the dual stats simply double flow back to the rad? I guess you need a rad modification for two return hoses? I've never seen one before.
I also noticed here that the GM engineer said if you flow to fast through the engine then you will not be absorbing enough heat from the metal surfaces and you will produce a false reading of lower (ECT)engine temp. So I guess that means that they have already figured out that the HO pump and dual stats is probably the maximum flow you would want. Have I got this right?
thanks for your feedback
If you add flow to the back of the heads at sufficient pressure to overcome the flow from the block then you cool the heads at the expense of flow through the block. which will get hotter.
If you could figure out a way to remove the hot water and replace it with cooler water then it would help.
Correct. Short of making sure the system is as healthy as it can be (clean and operating well), that's about it. Optimizing injection timing and boost levels will reduce temps under load as well as any other method.Quote:
Originally Posted by tomtaylor
No. The dual stat upgrade is OEM equipment for 1997+ models (and late 1996). The HO water pump is the same as your original, except for the output volume. It's a parts swap.Quote:
Do the dual stats simply double flow back to the rad? I guess you need a rad modification for two return hoses? I've never seen one before.
Hogwash! Any engineer who would say that is no engineer.Quote:
I also noticed here that the GM engineer said if you flow to fast through the engine then you will not be absorbing enough heat from the metal surfaces and you will produce a false reading of lower (ECT)engine temp. So I guess that means that they have already figured out that the HO pump and dual stats is probably the maximum flow you would want. Have I got this right?
thanks for your feedback
Quote:
Originally Posted by tomtaylor
To add to what DM said, "dwell time" is important for either absorbing heat in the engine or releasing heat in the radiator, but there is a fairly wide range that'll work fine. A longer dwell time in the radiator is important too.
It's important to understand the reason why the GM engineers increased coolant flow rate through the engine in the late 1996-early 1997 engines - to help prevent cylinder head cracking... Increasing flow rate through the heads helps to sweep the steam vapor layer off the exhaust runners in the heads and allow the coolant to better absorb the heat directly from the cast iron heads.
The coolant passages in the cylinder heads and head gaskets were all designed to move coolant in certain directions and at certain volumes. Any cooling system mod that reduces flow through the cylinder heads works against what the GM 6.5 cooling system engineers learned in the laboratory and ultimately applied to engine production.
I will chime in here for a bit of input.
Lest say right off, I agree 100% with Maverick and More Power.
The Bypass gimick is just that, a GIMICK TO MAKE SOMEONE $$$$$$$$$$$$$$ and to try and fool people into believing that all is well.
The coolant flow through the 6.2/6.5 engines must work as it was designed in order to keep the engine cooling properly.
Head gaskets do go away on these engines, but usually its not until around 200K miles or so.
The gaskets used on the older 6.2 engines (80's) were of a different design than the ones used on the 6.5 later in the production sequence.
Currently the best gasket to use in a 6.2 is the late style 6.5 gaskets produced by Felpro.
One of the most overlooked items in the cooling system is the radiator, followed closely by the fan clutch.
The original equipment fan clutches were a POS. GM raised the temperature at which the clutch "Hooked UP" after the myriad of whinning complaints they had on the mid 80's pickups/Burbs/Blazers about FAN NOISE
I had a customer once that swore his tranny was slipping when he was in the mountains and pulling hard.
I checked the tranny and all was fine. He insisted that I rebuild the tranny, install a cooler, a shift kit and a special torque converter.
OOOOOOOK, so we did all that. Two weeks later the fellow came back, madder than a boiled owl, tranny was slipping again :eek:
Nope, that was not the case. I kept the rig for a weekend and took it over the mountains for a family outing.
As soon as the engine temp would reach about 200 (gauge) the fan would howl like crazy and the temps would drop right off
I took the rig back and explained the situation to the owner, he was not convinced so I installed a Tach in the vehicle and had him watch that.
Only after seeing that when the engine fan was howling, the RPM did not climb was he convinced.
I digress
Now GM was fed up with all the whiners, so they raised the temps at which the clutches engaged plus the fan designs were changed and the overall fan speed (clutch connection) was altered so the noise level was dropped off to a less noticeable level.
Soooooooo these are some of the reasons why the cooling issues have happened.
The radiators also are of concern, as the size and cooling capacity is marginal when new, and after 100K miles or more the cores tend to "SILT" in down in the areas that have a slower flow rate.
The cooling air passages also tend to plug up with Bugs, dirt and other crap that gets ignored.
The results are an engine that continually runs too hot.
The cooling system upgrade with the new HO water pump and dual stats is a great addition, but the radiator should be changed out too (high milers)
The other issue in the radiators is the crap that sticks to the inside of the cooling water tubes, this being deposits from minerals in "TAP" water used in the coolant mix.
These deposits through time and heat collect and insulate the coolant from the metal tubes, thus blocking the rejection of heat.
I have replaced radiators in 6.5 trucks that had heating issues and the problems go away, instantly.
The raiators looked fine, until you cut them open and took a good look inside.
A 6.5 rig with a fresh radiator, a good water pump and Stat/stats plus a fan that will hook up when the air coming through the radiator gets to about 210F, will cool just fine.
Now if your talking H1 Hummers, thats a horse of a totally different color.
The airflow through the radiator on these must pass such a torturous path that the rigs are prone to cooling issues.
The radiator mounting position is part of the problem, but we are not going to redesign the Hummer here.
Clean radiator, good fan clutch, upgraded water pump and dual stats and the thing will cool fine without the need for add on hoses, fittings and other such nonsense.
In fact, just a clean radiator and a good fan clutch and most rigs will do fine without the HO pump and dual stats.
Missy
Hey everyone thanks for sharing the excellent info, learning alot here, still not fully clear on how the dual stat unit makes a difference. What exactly does this unit do that the old one does not? Is the turbo creating different temp characteristics on each side of the engine? thanks.
The dual thermostat is not different than a single, other than having 2 stats in parallel. The coolant crossover contains 2 thermostats, with 2 inlets and 1 outlet, same as the single. This also offers an option for thermostats with different temp standards, which can be beneficial, and is OEM on Duramax engines.Quote:
Originally Posted by tomtaylor
Thanks, I guess what I was looking for was in one of Jim's articles about system flow rates. The single stat doesnt keep up with the flow rate of the HO pump so a quick & cheap fix was to design a dual stat X-over that flows high enough for that pump, simple as that.
The dual Xover has a major increase in flow rate through the bypass port so the water in the block does not stagnate and allow steam pockets to form and result in Hot spots.
The other benefit is an increased flow through he radiator.
The radiator flow increase is not huge, but beneficial.
The major difference is the overall coolant flow rate through the block.
A much faster flow stirs up the entire cooling area in the heads and keeps stagnant areas with little or no flow from forming.
The coolant flows through the block, in and around the cylinders and then out the rear block port and up into the rear of the head. From here the water flows forward through the heads and up into the crossover.
During closed thermostat running the coolant flow rate on the old single stat system was much much slower, allowing the stagnation of coolant in various portions of the heads and block.
Velocity is the key here to keep these areas moving and steam pocket formation to a minimum.
The original single stat system was not bad, If the stock type stat was used.
A non stock stat without the proper base on it would alter the bypass flow rate and adversely affect the cooling ability.
The original stat had a baffle of sorts on the bottom of the stat that modified the flow back into the pump during the time that the coolant was flowing to the radiator.
The baffle on the stat would close of the bypass port to a great degree and keep coolant going to the radiator.
The wrong stat would allow too much coolant to back feed into the pump instead of going to the radiator.
The new dual system is a good setup.
Missy
Great thanks for adding in those details, so the purpose of the bypass circuit is to keep coolant on the move until the stat opens and this helps prevent those hot spots/steam pockets from forming, correct?
I seem to recall seeing a coolant product advertised here a while back that claimed to reduce or eliminate this steam layer and then I saw a comment from Jim about it maybe didn't live upto it's claim or something like that, does anyone recall this?
No. The "bypass" is there to circulate coolant to the thermostat to keep it "in touch" with actual engine/head coolant temperatures. This is necessary when the thermostat is "detached" from the engine. Meaning, because it is in a crossover manifold, the thermostat may not be exposed to actual coolant temperatures occurring in the engine. circulating a small amount of coolant at all times keeps the thermostat in contact with engine temperature coolant. Many other engine designs (such as the traditional SBC/BBC) don't have this problem, because the thermostat is actually housed in the engine.Quote:
Originally Posted by tomtaylor
The HO water pump creates a condition of higher coolant velocity, which helps reduce the condition of "film boil", which causes the heat/steam pockets.
"Water Wetter" is the product. Its purpose is to reduce the condition of film boil to prevent cylinder wall detonation. This is a serious condition with, primarily (in the light truck world), Navistar 6.9 and 7.3 IDI engines. The "wet" cylinder sleeves would actually erode to the point of failure without the correct coolant additive. None of the GM engines have ever suffered this condition. The additive has never proved, that I've seen, to help with actually cooling the engine.Quote:
I seem to recall seeing a coolant product advertised here a while back that claimed to reduce or eliminate this steam layer and then I saw a comment from Jim about it maybe didn't live upto it's claim or something like that, does anyone recall this?
If you are concerned with steam pockets/layers, use NPG coolant. No water, so no boil. It works very well, but is expensive. If you never have a leak, it could be your last coolant service on that vehicle. Ever.
Thanks again for the great details, I will definately look up the NPG product although I don't think I'm in need of it. I am just trying to understand as much as I can about these engines.
I would like to ask though with all the discussion here about lowering coolant temp is there not an ideal engine operating temp to maintain thermal efficiency to get the most out of your power and economy? Is this operating temp a narrow or broad range?
The ideal engine temperature to achieve optimal thermal efficiency, power and economy far exceeds the abilities of traditional engine cooling system components, coolant fluid, and engine components. Essentially, the coolant medium is the limiting factor at the lowest level. The use of NPG coolant removes this factor, and steps the process to the next level: the components. 240°F is about the maximum with EG/water coolant at 15 PSI. The ~200°F operating temperature standard for almost all passenger vehicles allows for a bit of flexibility to keep the temperature at a safe level, with a buffer for overheat conditions. Above that, components such as hoses and seals become vulnerable to heat damage.
The problem isn't so much what temperature can be withstood, but what temperature can be maintained and/or managed. Lowering an engine's operating temperature (by installing lower rated thermostats, for example) to address a frequent overheat condition is most often a band-aid to mask a problem of a less than optimal cooling system, or exceeded mechanical/physical limits (too much power). The lower operating temperature only increases the range of the buffer. In most cases, the problem isn't the maximum temperature, but the ability to control the temperature once it reaches a point of no return. This is why we hear of some trucks that can do a job without ever overheating, while others boil over, all else being equal. Heat generated by burning fuel is used in two ways, either by converting it to forward motion, or shedding it to the environment (cooling system). A 100% efficient powerplant would remain at ambient temperature, all the time, always have power limited only by the fuel consumed, and be absolutely silent. Unfortunately, we can't achieve that, so we have to settle for a middle ground. Some heat energy is used to move you down the road, and the rest is returned to the environment, one way or another.
Just a quick comment on cooling system performance. I have found a relationship between engine blow by and cooling system performance.
This has possibly been related to efficiency as with modern ring, piston design oil consumption is usually excessive long after engine inefficiency has caused problems with cooling. Also it seems to me that when ever I have a "hot" running engine the damn thing seems to go forever.
Some t-stat facts....
GM installed 180 degree t-stats in the 1980s 6.2L diesel engines.
GM upped the temp to 195 in the 1990s.
Peninsular Diesel installed (and may still) 160 degree t-stats in their marine 6.2/6.5 diesels.
Jim
The main reason that the Manuf's use the 195F stats is to maintain emission levels.
The higher temps allow for a little better burn and a little more efficiency.
The cooler temp stats allows the engine to run a lot cooler and overall with place less thermal stress on the engine components.
More heat equals more expansion and contraction of the block and heads.
As these components expand and contract (They are Moving) :eek:
All this movement eventually causes issues, or at least it can.
After having been inside many many 6.2/6.5 engines, I have seen some of the damndest messes of cracks.\
Cracks in cast iron are cuased or at least can be caused by many things.
A poorly cured block, when subjected to high temperatures moves around a lot duirng its operational cycles, and in many cases, due to the fact that everything is all bolted up tight, can't move enough to relieve itself.
I have seen mainline cracks at the register fit area that have spread open as much as .030". Now this is not at all a good thing.
A hairline crack can occur due to stresses, but to have a crack open up means that stuff is moving, changing shape and "Normalizing"
A 6.2/6.5 block thats crack free and has many many miles on it will likely be fine for an almost indefinate time period.
The heat level at which these engines operate can certainly effect the whole picture.
I prefer the 180F stat as a good compromise in temp level.
Good enough to allow the oil to lose any moisture and flow well, and also a level that the thermal stresses are manageable.
If you look at many of the 6.5 equipped trucks, you will see a dash gauge (coolant tamp) that has a RED line of 250F ++
This is crazy.
I have spoken with a few owners who tow trailers and tell of long periods of towing in the heat of summer with the gauge at or near the 240 mark :eek:
This sort of temperature is just cooking the engine.
Expansion is at its maximum and the stress on the components is off the charts.
A properly set up and maintained cooling system in these rigs can and will maintain 200 F under most conditions.
Even in the extreme heat of the desert, the cooling system should be able to deal with the heat and manage it at near the 200 F mark
Missy
In the far distant past I had a lot toto do with cat engines and the best examples I can come up with to illustrate my findings regarding the relationship between higher "controlled" engine temps and operating under lower temps are as follows.
3512, 3516 in 785b and 789b trucks at only 12/14 thou hrs rhs liner wear (water pump side) in excess of 14 thou lhs liners less than 5/6 thou.
3516 gen sets 1.2 Meg operating at coolant temps of 100c / 110c 18000hrs +.
Less than 10 thou on average both banks.
D7g dozers doing seismic work ie hi speed low load 2,500 hours valve guides u/s. Same dozers pushing gravel 8,000 hrs +.
Why does this not apply with the 6.5?
I am not convinced that sulpher is the sole culprit.
Would really appreciate your thoughts.
Steve.
Discussing the ideal thermostat temperature setting is a little off topic to this thread, but... I've thought about it too....Quote:
Originally Posted by scarmic
First, there is a big difference between a constant load operating cycle (i.e. genset) and a variable duty-cycle (i.e. light-duty pickup).
1- A case can be made where the hotter the operating environment, the more failures the original DS4 PMD suffered.
2- If the thermostat setting was nearer to the critical level where the electronic DS4 system went into limp mode (programmed de-fueling), the more often that might occur and it would present the driver with less time to prevent an overheat situation.
3- A normal and healthy diesel engine and cooling system in a light-duty pickup doesn't reach the level of the t-stat setting unless it's hot outside or there is a load on the engine - especially in cool weather. A higher t-stat setting would produce larger engine temperature swings. Large and frequent thermal cycles affect the longevity of the gaskets and other engine components. A Genset, on the other hand doesn't have to deal with the same frequency or magnitude of thermal cycles that a pickup engine does.
That said, there's nothing stopping anyone from using whatever temp thermostat they choose or have available to them. I prefer a 180 degree t-stat, but that's just me... ;)
So then our issue is not so much the operating temp as it is the control of that temp (temp range) as it relates to the flow rate and quantity of coolant on reserve(rad). This is an easily solved problem in a constant load environment where stationary power is needed but more challenging in variable load environment like motor vehicle applications. So upsizing the coolant reserve(rad) and flow rate, when possible, is always a good idea as well as the air flow across the rad. Thanks for the info again.Quote:
Originally Posted by DmaxMaverick