What did you do with your GMT400 today...or yesterday....

[Husker6.5]

Hmm mine must be the rare one then, from looking at pics of them. But your description of the rare style a few post up doesn’t seem to match the pics I’m finding, could you include pics?

IF I had one, I'd definitely post pictures of it. Hence, per my post above, I'm going diving through 100+ issues of DieselPower magazine to find the article on the 6.5 build that used the rare large single stat crossover, as I know there pics of the crossover.

 

[J_dude]

IF I had one, I'd definitely post pictures of it. Hence, per my post above, I'm going diving through 100+ issues of DieselPower magazine to find the article on the 6.5 build that used the rare large single stat crossover, as I know there pics of the crossover.

Here is mine if that’s of any help.

 

[Will L.]

Right, the argument becomes what is better:
More coolant at 200° going through the thermostat to radiator even though a large portion is going back into the engine, or

The single stat that flows 100% of its coolant to the radiator so none of the already 200° water goes back into the engine.

Different people have tested different set ups with varied results.
In Las Vegas fleets- where the humidity is low so it tasks the radiator more, and the a/c is always on max recirculate shedding more heat from condenser to radiator, and obviously stupid hot - We found the single stat with block off out performed the duals even if they had the restrictor in the 1” line. The fuel company is the one that serviced Death Valley and it made a big difference there also.

Down in Phoenix where it is hotter but has a little more humidity- Our few trucks that ran there did better with single also. I believe @WarWagon had same experience down there.

So, I get the dual flow more, but the duals were enacted by GM, then the next year is when they added the restrictor fitting. As mentioned the thermostats sticking shut was a known issue and cost gm a lot of warranty engines. So they went to the duals so one can fail shut and the engine doesn’t grenade right away. That was yet another win for dexcool. The 1995 introduction of dexcool was building up its mud of nitrate and silicates in the mechanics of the thermostat. I remember reading numbers when I worked in the dealership that near 15 % of the blown engines had stuck thermostat. In the fleet after we lost the 2nd engine because of the “dexcooked” thermostat- we flushed them all and went back to green. NEVER AGAIN lost and engine to dexcool.
But from the flushing and seeing how bad it plugged radiators- we ended up replacing something like 35 radiators.

We did have one mechanic that was convinced the duals would have worked better once green is as in use. So we tried 4 trucks in comparison- normal use wasn’t a major difference but the heavy worked ones or high heat areas, the single stat clearly outperformed.

 

[Husker6.5]

View attachment 76706
Here is mine if that’s of any help.

YES! That is one of the rare rear exit single stat x-overs! Most 96 used the single stat that had the outlet facing forward toward the radiator like 92-95 did. I also notice that you have the A/C delete idler pulley/bracket on it, too. At 60+ years old and trying to remember the article from 10+ years ago, I thought that the x-over also had a squared body and a 4 bolt cover.

 

[Big T]

These are going in my son’s ‘94. I’ll do before and after measurements to see if they improve the steering radius.

 

[Husker6.5]

Of course, @J_dude, living in Saskatchewan you don't really need A/C, do you? Now, fitting in a Suburban dual heater set up. . .

 

[J_dude]

Of course, @J_dude, living in Saskatchewan you don't really need A/C, do you? Now, fitting in a Suburban dual heater set up. . .

Haha yeah for most of the year I really don’t miss it, this summer though has been pretty toasty, we’ve had some near record high temps. But for what I use the truck for it wouldn’t be worth fixing the A/C, would only ever need it once a day on my drive home from work and besides, better fuel economy if you don’t use it .

I find the heaters on these trucks are really quite sufficient actually, it’s my Dodge that needs help in that department, getting that thing to warm up at -30C is difficult, even with the rad mostly blocked off the temp drops right down when you turn the cabin heat on, and I’ve got a hotter t-stat in her!

 

[dbrannon79]

@J_dude what year dodge do you have? my 99 ram 1500 will burn you out of the cab!! when it gets cold enough to ice the windshield, I never warm the truck with the defrosters on. have always feared how hot the air gets that it would bust the glass! lol

back when I was turning wrenches on my first job, our boss (my wife's uncle) had a 96 chevy 1500 shop truck that this very thing happened. he had left it out of the shop one night it has collected ice on the windshield. he warmed it up with the defrosters on high which busted the glass on it!!

 

[J_dude]

@J_dude what year dodge do you have? my 99 ram 1500 will burn you out of the cab!! when it gets cold enough to ice the windshield, I never warm the truck with the defrosters on. have always feared how hot the air gets that it would bust the glass! lol

back when I was turning wrenches on my first job, our boss (my wife's uncle) had a 96 chevy 1500 shop truck that this very thing happened. he had left it out of the shop one night it has collected ice on the windshield. he warmed it up with the defrosters on high which busted the glass on it!!

‘96 with the Cummins, they do not put out heat like the gassers, partly because the cooling system is overbuilt (not typically a bad thing) and partly because the heater system is underbuilt .

 

[J_dude]

@J_dude what year dodge do you have? my 99 ram 1500 will burn you out of the cab!! when it gets cold enough to ice the windshield, I never warm the truck with the defrosters on. have always feared how hot the air gets that it would bust the glass! lol

back when I was turning wrenches on my first job, our boss (my wife's uncle) had a 96 chevy 1500 shop truck that this very thing happened. he had left it out of the shop one night it has collected ice on the windshield. he warmed it up with the defrosters on high which busted the glass on it!!

Oh and yes, when it’s good and cold the glass concern is very real, just not on my diesels, they warm up too slowly lol. My dad’s ‘96 Vortec cracked a nearly new windshield in just such a manner.

 

[dbrannon79]

‘96 with the Cummins, they do not put out heat like the gassers, partly because the cooling system is overbuilt (not typically a bad thing) and partly because the heater system is underbuilt .

Yeah the diesels are much slower at warming up.

 

[J_dude]

Yeah the diesels are much slower at warming up.

Probably would heat like crazy if I was towing something though, after all that’s what the truck was designed for lol.

 

[dbrannon79]

@Big T iirc you posted that you had already replaced your radiator along with all the upgrades you did. I assume the fan clutch is kicking in when the temps are up. I am suspecting you may have a failing t-stat. I would think it's possible that it's opening up too soon and staying full flow with the upgraded higher flowing water pump circulating the coolant so fast it doesn't have enough time to cool down thus temps are climbing when under a heavier load or the engine rpm is up.

I have experienced this on gassers around here in Texas heat with the humidity is real high, lots of folks think running a low temp stat for normal driving on freeways or hauling will help. But it does the exact opposite allowing coolant to keep flowing fast through the radiator to the point that it begins to get hotter. around here the lowest you want to go is 180. and that's mainly for in town driving only. for highway driving or heavy loads it's best to keep the factory temp stat along with using the OEM brands.

on the OEM brands, I learned this the hard way. I have had to replace the stat on my rig about 5 times due to every time I have to do any work that requires the coolant to be drained below the level of the stat, I begin to see issues with it trying to stick on me.

that might be too what is happening, if you did any work on the cooling system after installing the current stat.

 

[Big T]

@Big T iirc you posted that you had already replaced your radiator along with all the upgrades you did. I assume the fan clutch is kicking in when the temps are up. I am suspecting you may have a failing t-stat. I would think it's possible that it's opening up too soon and staying full flow with the upgraded higher flowing water pump circulating the coolant so fast it doesn't have enough time to cool down thus temps are climbing when under a heavier load or the engine rpm is up.

I have experienced this on gassers around here in Texas heat with the humidity is real high, lots of folks think running a low temp stat for normal driving on freeways or hauling will help. But it does the exact opposite allowing coolant to keep flowing fast through the radiator to the point that it begins to get hotter. around here the lowest you want to go is 180. and that's mainly for in town driving only. for highway driving or heavy loads it's best to keep the factory temp stat along with using the OEM brands.

on the OEM brands, I learned this the hard way. I have had to replace the stat on my rig about 5 times due to every time I have to do any work that requires the coolant to be drained below the level of the stat, I begin to see issues with it trying to stick on me.

that might be too what is happening, if you did any work on the cooling system after installing the current stat.

You may be confusing my work on the ‘99 with the work on my son’s ‘94. I recently replace the radiator on the ‘99 as the OEM started leaking. I installed a Champion radiator.

My son has replaced the radiator on the ‘94, but that was 4+ years back and it sat in my backyard for 3 years with injection pump issues. Also replaced his fan clutch. He has an HO waterpump, single t-stat crossover w/ either 190 or 195 AC Delco t-stats, duramax spin on fan blade and green coolant. Guess I could start with cheap things like a new t-stat.

 

[Husker6.5]

The high output 130gpm water pump on a <95 single stat x-over is just barely slightly better than running the from the factory 80gpm pump. Simple mathematics of Bernoulli's Principles of Hydraulic Dynamics.

Since fluids (such as water) are uncompressible, the smallest restriction in the system limits the volume that can pass through that point. Trying to cram more volume through that point (higher flow water pump) only results in a slightly higher volume passing through that restriction, and HIGHER back pressure behind the the restriction (as high as 30-60psi with a partially open/stuck shut t-stat OR a t-stat not designed to flow the volume of water the pump is designed to flow) - that will actually SLOW the movement of fluid behind the restriction. Which will keep heat in the coolant behind the pump, as well as limit the amount of even now hotter coolant that makes it to the radiator.

The point is, you want to balance the flow rate of the pump (gpm) to the flow rate of the most restrictive point in the system - which is always the thermostat - to limit back pressure to a minimal amount (a little back pressure is good, it allows more heat transfer to the coolant it's in contact with longer, too much back pressure is bad because the hot coolant has nowhere to go).

With a thermostat, the flow is NOT determined by the diameter of the flange of the t-stat, but the diameter of the valve seat inside the t-stat and how high the valve is lifted off the seat at full open. The actual area for the coolant to flow through is the circumference of the valve seat x's the height it is lifted. So, circumference is the diameter multiplied by pi.

Let's use this pretty easy example, typical for say a 2.2L gasser:
Circumference x Height = Area
Circumference = Diameter x pi
Valve seat diameter -> 1.25"
Lift height wide open -> 0.25"
So, [1.25" x 3.14(pi)) x 0.25" = Area
3.925" x 0.25" = Area
0.98"² = Area - just less than one square inch, 3n open 3/4" hose/pipe has 0.442"² area.
By comparison, at a standard 60psi pressure of a municipal water system, with 3/4" house pipes, faucet and 3/4 garden hose, you flow 113 gallons per minute. A vehicle cooling system runs nowhere near that psi of pressure, it is designed to run at just a few psi difference on either side of the t-stat at its wide open and a very low system pressure of 15psi overall.

The 130gpm water pump you're running on your son's '94 was designed as an answer in the '96 production on the assembly line to the overheating in the rear of the passenger head/cylinder, and to flow almost double the earlier 6.2/6.5 80gpm. The engineering answer was the early, "temporary" large single t-stat housing and the large diameter, high lift (nearly ½" at wide open) valve t-stat in it. Look at @J_dude 's photo of his 96 special t-stat x-over. Look at how large and deep the "bowl" is and how tall the outlet housing is to the spigot - that was to both allow enough coolant to flow into the bowl behind the t-stat AND enough depth/height for the high lift t-stat. It was the "fix" to allow the new 130 gpm (unbalanced flow) water pump to move the volume it was designed to. But that casting of x-over and outlet housing was difficult to both cast and machine (expensive). The Bean Counters quickly intervened with the Engineering Department and the result was the easier to cast and machine (cheaper) rectangular box with two runners attached and simple outlet cover using two common standard t-stats (cheaper) that combined flowed close to the "temporary" design.

Want your son's 94 to run cooler? Remove the restriction that's preventing the 130gpm from flowing as it was designed to, and is creating backpressure which is also holding heat in the engine by doing so. Swap out the "choke point" 94-95 x-over and put a 97+ one on with AC Delco/GM t-stats in it so that 130gpm water pump can "breathe" freely and move the coolant it was designed to through the engine, out of it past the t-stats and through the radiator.

Also, as @Will L. pointed out earlier and I agree with him 100%, Water Wetter does make a difference. It is a surfactant that enhances the transfer of heat from metal to water and while you may not see a difference on the temp gauge (because the t-stats regulate the coolant temperature to a couple of degrees of their operating temperature) but it does help pull more BTU's out of the engine into the coolant and then rids those BTU's from the coolant to the core of the radiator which then rids the BTU's to the air flowing through it. The temperature drop they claim to coolant temp comes from running a racing engine, which does NOT run with a t-stat in it, at speed and measured the difference without and with Water Wetter in the cooling system. Why do they call them "warm up laps" before a race? Because that's exactly what they're doing, bringing their t-statless engines up to operating temperature and maximum performance efficiency before starting the race.

Remove the restriction and put a 97+ dual t-stat x-over on your son's 94 and you'll see the coolant temps drop down to where your 99 runs now that the 130gpm pump can carry all that heat away from the engine unrestricted.

 

[Husker6.5]

Yeah the diesels are much slower at warming up.

Unless you plug in and use a 1000W block heater (or a 750W in each side of the block) when you park after running. FAR easier to keep the block and coolant maintained at 100-120°F (38-50°C for the Cannuck) than it is to heat up from -22°F (-30°C) to 100-120°F (38-50°C) three hours later to start it.

 

[Big T]

The high output 130gpm water pump on a <95 single stat x-over is just barely slightly better than running the from the factory 80gpm pump. Simple mathematics of Bernoulli's Principles of Hydraulic Dynamics.

Since fluids (such as water) are uncompressible, the smallest restriction in the system limits the volume that can pass through that point. Trying to cram more volume through that point (higher flow water pump) only results in a slightly higher volume passing through that restriction, and HIGHER back pressure behind the the restriction (as high as 30-60psi with a partially open/stuck shut t-stat OR a t-stat not designed to flow the volume of water the pump is designed to flow) - that will actually SLOW the movement of fluid behind the restriction. Which will keep heat in the coolant behind the pump, as well as limit the amount of even now hotter coolant that makes it to the radiator.

The point is, you want to balance the flow rate of the pump (gpm) to the flow rate of the most restrictive point in the system - which is always the thermostat - to limit back pressure to a minimal amount (a little back pressure is good, it allows more heat transfer to the coolant it's in contact with longer, too much back pressure is bad because the hot coolant has nowhere to go).

With a thermostat, the flow is NOT determined by the diameter of the flange of the t-stat, but the diameter of the valve seat inside the t-stat and how high the valve is lifted off the seat at full open. The actual area for the coolant to flow through is the circumference of the valve seat x's the height it is lifted. So, circumference is the diameter multiplied by pi.

Let's use this pretty easy example, typical for say a 2.2L gasser:
Circumference x Height = Area
Circumference = Diameter x pi
Valve seat diameter -> 1.25"
Lift height wide open -> 0.25"
So, [1.25" x 3.14(pi)) x 0.25" = Area
3.925" x 0.25" = Area
0.98"² = Area - just less than one square inch, 3n open 3/4" hose/pipe has 0.442"² area.
By comparison, at a standard 60psi pressure of a municipal water system, with 3/4" house pipes, faucet and 3/4 garden hose, you flow 113 gallons per minute. A vehicle cooling system runs nowhere near that psi of pressure, it is designed to run at just a few psi difference on either side of the t-stat at its wide open and a very low system pressure of 15psi overall.

The 130gpm water pump you're running on your son's '94 was designed as an answer in the '96 production on the assembly line to the overheating in the rear of the passenger head/cylinder, and to flow almost double the earlier 6.2/6.5 80gpm. The engineering answer was the early, "temporary" large single t-stat housing and the large diameter, high lift (nearly ½" at wide open) valve t-stat in it. Look at @J_dude 's photo of his 96 special t-stat x-over. Look at how large and deep the "bowl" is and how tall the outlet housing is to the spigot - that was to both allow enough coolant to flow into the bowl behind the t-stat AND enough depth/height for the high lift t-stat. It was the "fix" to allow the new 130 gpm (unbalanced flow) water pump to move the volume it was designed to. But that casting of x-over and outlet housing was difficult to both cast and machine (expensive). The Bean Counters quickly intervened with the Engineering Department and the result was the easier to cast and machine (cheaper) rectangular box with two runners attached and simple outlet cover using two common standard t-stats (cheaper) that combined flowed close to the "temporary" design.

Want your son's 94 to run cooler? Remove the restriction that's preventing the 130gpm from flowing as it was designed to, and is creating backpressure which is also holding heat in the engine by doing so. Swap out the "choke point" 94-95 x-over and put a 97+ one on with AC Delco/GM t-stats in it so that 130gpm water pump can "breathe" freely and move the coolant it was designed to through the engine, out of it past the t-stats and through the radiator.

Also, as @Will L. pointed out earlier and I agree with him 100%, Water Wetter does make a difference. It is a surfactant that enhances the transfer of heat from metal to water and while you may not see a difference on the temp gauge (because the t-stats regulate the coolant temperature to a couple of degrees of their operating temperature) but it does help pull more BTU's out of the engine into the coolant and then rids those BTU's from the coolant to the core of the radiator which then rids the BTU's to the air flowing through it. The temperature drop they claim to coolant temp comes from running a racing engine, which does NOT run with a t-stat in it, at speed and measured the difference without and with Water Wetter in the cooling system. Why do they call them "warm up laps" before a race? Because that's exactly what they're doing, bringing their t-statless engines up to operating temperature and maximum performance efficiency before starting the race.

Remove the restriction and put a 97+ dual t-stat x-over on your son's 94 and you'll see the coolant temps drop down to where your 99 runs now that the 130gpm pump can carry all that heat away from the engine unrestricted.

We have a dual t-stat X-over, so will put that on. Everyone said the single was superior so we left it on. The dual x-over makes playing with the IP a lot harder.

 

[jrsavoie]

You may be confusing my work on the ‘99 with the work on my son’s ‘94. I recently replace the radiator on the ‘99 as the OEM started leaking. I installed a Champion radiator.

My son has replaced the radiator on the ‘94, but that was 4+ years back and it sat in my backyard for 3 years with injection pump issues. Also replaced his fan clutch. He has an HO waterpump, single t-stat crossover w/ either 190 or 195 AC Delco t-stats, duramax spin on fan blade and green coolant. Guess I could start with cheap things like a new t-stat.

Test and verify

 

[jrsavoie]

We have a dual t-stat X-over, so will put that on. Everyone said the single was superior so we left it on. The dual x-over makes playing with the IP a lot harder.

I would just leave the single stat cross over alone

 

[dbrannon79]

I am curious on this dual x-over housing. I have the 95 single setup on mine with the HO pump. I have noticed that when I'm on the freeway my temp will get up to a 200 and the EV fan will turn on, cool everything off and then cycle off again. I have a 180 stat installed. when in town it rarley turns the ev fan clutch on except for when the AC is on. it never overheats or goes any higher than 200 ( where I have the fan controller set at. And I run empty 90% of the time.

@Husker6.5 you have me curious if the dual x-over will help with this.