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

[SnowDrift]

Thank you @Glagulator

 

[SnowDrift]

Husker said this:

When they switched sides with the accessories in 96IIRC there was a one year single stat before the dual stats. They're unicorns anymore I had one that I let get away not realizing what I had. It allows the DB2 pump to fit better on later year rigs

If a guy could obtain the unicorn, it sounds as though it's capable of doing the job, though, and allows a better fit for the DB2. Is that about right? I still wonder how much that '96 design will flow in comparison to the later dual thermostat design.

 

[Big T]

Husker said this:
View attachment 98481

If a guy could obtain the unicorn, it sounds as though it's capable of doing the job, though, and allows a better fit for the DB2. Is that about right? I still wonder how much that '96 design will flow in comparison to the later dual thermostat design.

This is interesting. Because of all the proponents of the single stat, I left it on the ‘94 which has the upgraded 130gpm water pump and the Dmax fan. However, it still runs warmer than my ‘99. I do have a dual stat crossover on the engine we took out of the ‘95, so I might just put that on the ‘94 based on Husker’s comments.

 

[Will L.]

Husker said this:
View attachment 98481

If a guy could obtain the unicorn, it sounds as though it's capable of doing the job, though, and allows a better fit for the DB2. Is that about right? I still wonder how much that '96 design will flow in comparison to the later dual thermostat design.

Look in my signature. Block off thermostat option. Follow the link.
Look at the size of those two. If a person is worried about flow restrictions through thermostat(s)- this would have maximum ability.

Also for the dual stats vs single-
It was already actually tested years ago. The single wins.
Someone can do it again if they feel the need.

I’ll try walking through it.
lets say the single stat has 2 square inch of flow area.
And the smaller duals has 1.25 each for 2.5. Now
Account for
100% of the coolant on the single going to the radiator. 2x100=200
75% of the duals IF you have a BRF. 2.5x.75=1.875.

Maybe my 1.25 is wrong?!!? Maybe it’s 1.5x2=3. Then 3x.75=2.25?????
Number theory is cute- but how much actually flows into the radiator and REMOVES HEAT FROM THE ENGINE- that’s what counts.

FOR EVERY PERSON you can find that has ran both the duals and the blockoff single stat- I am willing to bet there is 4 who attest to the single keeping temps more stable for less fan time, cooling off quicker when hot. Warming up faster on cold mornings.
You can find @WarWagon accounts of it here and other forums long before I joined.

Run what you have if it works. If not-then play with it. But as hard as it is to find any rare part- I would say get the ones that Nate found that are in my signature.

 

[dbrannon79]

Well I haven't been home long getting off work, maybe an hour, but I went outside to look at something on the truck and go out there to see this in the driveway! looks like I might be pulling the timing cover sooner than I want to. I know it's been leaking ever since I got the truck, but it hasn't been bad enough to warrant me to tear it down with all the work and time required to seal this up. I was hoping I could leave it be until I find another engine since this one is so worn out.




It's leaking from the passengers side top of the timing cover right where the coolant passage is from the pump on the block side. second pic is zoomed in right underneath the AC compressor near the fitting on the block for the turbo oil feed line.

 

[SnowDrift]

Mine got warmer than I like to see this past summer pulling our fifth wheel on flat ground for about a 10 mile trip. I had to turn off the A/C and haven't had to do that since before I replaced my radiator when I suspect it was plugged.

The cavitation mentioned in that dieselpage article makes sense and causes me to wonder if those involved weren't onto something.

Seems strange that a corporation would go to the expense to create a new part if they had one that was already superior.

I have looked at the parts in the link you mentioned several times.

I was just wondering if it would be worth the wait for the rare part if it has adequate flow.

 

[Big T]

Look in my signature. Block off thermostat option. Follow the link.
Look at the size of those two. If a person is worried about flow restrictions through thermostat(s)- this would have maximum ability.

Also for the dual stats vs single-
It was already actually tested years ago. The single wins.
Someone can do it again if they feel the need.

I’ll try walking through it.
lets say the single stat has 2 square inch of flow area.
And the smaller duals has 1.25 each for 2.5. Now
Account for
100% of the coolant on the single going to the radiator. 2x100=200
75% of the duals IF you have a BRF. 2.5x.75=1.875.

Maybe my 1.25 is wrong?!!? Maybe it’s 1.5x2=3. Then 3x.75=2.25?????
Number theory is cute- but how much actually flows into the radiator and REMOVES HEAT FROM THE ENGINE- that’s what counts.

FOR EVERY PERSON you can find that has ran both the duals and the blockoff single stat- I am willing to bet there is 4 who attest to the single keeping temps more stable for less fan time, cooling off quicker when hot. Warming up faster on cold mornings.
You can find @WarWagon accounts of it here and other forums long before I joined.

Run what you have if it works. If not-then play with it. But as hard as it is to find any rare part- I would say get the ones that Nate found that are in my signature.

Same components on my ‘94 and ‘99, except for single vs dual thermostat respectively. ‘94 runs at 195 to 200 a can easily hit 210 on a warm day. ‘99 runs at 187 and is mostly pegged there. It and rarely gets over 200 and you must be charging up a steep mountain grade in summer heat.

 

[SnowDrift]

Are you running the HO pump on both @Big T ?

 

[Will L.]

Ive done swaps on the same truck in fleet and on my personal 99 when we were trying to figure it out. To be fair, the 195 stat would move the ect gauge more but keep it steady under or at 195 where as the duals would allow the 210 to happen- exactly opposite of what Big T has in his two suburbans.
When I did the 180 stats and swapped between them- the duals would move between 175-190. The single 180 just lives within 5° of 180.

Keep in mind with mine i was paying attention to how often fan came on and the singles won that regardless of 180/195. This was still running stock fan, radiator, & what we know now as the balanced flow pump. Any old postings from me here or other places I called it the updated serpentine belt pump.

The other thing is my readings were with two quality temp gauges, one mechanical and one digital. The factory pos is a joke. In the fleet they all had an aftermarket mechanical gauge added reading right rear head.

Where he said can hit 210 on warm day- mine of a fleet truck that hits 210 a second time comes into the shop for repairs. You guys seen me say it-
195-200 all day is ok
210 watch the gauge ore than the road.
220 pull over and let idle to normal.

I’m not joking with that 210 - and if you are busy watching a gauge while driving then you are at elevated risk for an accident. That is a get you home/ to shop state. If you know you can hit 210 - fix it, it is broken.

Verify gauge
Clean the radiator inside outside, between stack components.
System flush
Clean & test fan clutch
Thermostat is highly suspicious-

GM went to the dual stats because they ate a bunch of engines when the factory stats were sticking closed. Having one of two stick closed means a controlled overheat. A single stat sticks closed and you over heat and over pressurize quickly. It’s been too many years to remember the brands right now- but GM changed suppliers over it. There was a design of using the dual thermostats that were both block off and the lower chamber came out into one return hose.
Some generators got them. But they had the db2 and oil fill on the valve cover. It was simply too bulky.
Going to the constant bypass was an undesirable compromise. Thats why they had that freshly retired guy redesign the duals and he came up with that restrictor. It wasn’t a simple drilled hole reducing the size- it was shaped inside to affect flow. The whole- put in part and drill it or weld up & drill was a jerry rig trying to imitate most of the effect after he died and GM couldn’t steal his idea.

 

[Big T]

Are you running the HO pump on both @Big T ?

Yes

 

[Big T]

Ive done swaps on the same truck in fleet and on my personal 99 when we were trying to figure it out. To be fair, the 195 stat would move the ect gauge more but keep it steady under or at 195 where as the duals would allow the 210 to happen- exactly opposite of what Big T has in his two suburbans.
When I did the 180 stats and swapped between them- the duals would move between 175-190. The single 180 just lives within 5° of 180.

Keep in mind with mine i was paying attention to how often fan came on and the singles won that regardless of 180/195. This was still running stock fan, radiator, & what we know now as the balanced flow pump. Any old postings from me here or other places I called it the updated serpentine belt pump.

The other thing is my readings were with two quality temp gauges, one mechanical and one digital. The factory pos is a joke. In the fleet they all had an aftermarket mechanical gauge added reading right rear head.

Where he said can hit 210 on warm day- mine of a fleet truck that hits 210 a second time comes into the shop for repairs. You guys seen me say it-
195-200 all day is ok
210 watch the gauge ore than the road.
220 pull over and let idle to normal.

I’m not joking with that 210 - and if you are busy watching a gauge while driving then you are at elevated risk for an accident. That is a get you home/ to shop state. If you know you can hit 210 - fix it, it is broken.

Verify gauge
Clean the radiator inside outside, between stack components.
System flush
Clean & test fan clutch
Thermostat is highly suspicious-

GM went to the dual stats because they ate a bunch of engines when the factory stats were sticking closed. Having one of two stick closed means a controlled overheat. A single stat sticks closed and you over heat and over pressurize quickly. It’s been too many years to remember the brands right now- but GM changed suppliers over it. There was a design of using the dual thermostats that were both block off and the lower chamber came out into one return hose.
Some generators got them. But they had the db2 and oil fill on the valve cover. It was simply too bulky.
Going to the constant bypass was an undesirable compromise. Thats why they had that freshly retired guy redesign the duals and he came up with that restrictor. It wasn’t a simple drilled hole reducing the size- it was shaped inside to affect flow. The whole- put in part and drill it or weld up & drill was a jerry rig trying to imitate most of the effect after he died and GM couldn’t steal his idea.

I’m going off the shitty dash gauges and the ‘94 gauge is really shitty and suspect. Down the road I’ll be getting a digital gauge cluster for the ‘94.

 

[SnowDrift]

Is this the article that was mentioned which Bill Heath wrote when the single thermostat housings became desirable?

 

[dbrannon79]

Not sure if this constitutes in the same manor as in Bill's article, but I did do AK's version of the cooling upgrade on my 95 a good while back. it still had the factory pump with the bolt on original fan clutch and the factory fan. I replaced it all with a GM pump for a 2000 6.5 that uses the spin-on clutch, also installed a electro-viscous clutch and fan blade from a 2010 express van with a duramax engine. The fan controller is a Hayden brand made for electric fans, but works the same for the clutch for engagement at temp. I can get the part numbers for the pump and all if needed to compare to what Bill's article shows if needed.

still has the factory aluminum / plastic tank radiator but was cleaned out as well as the cooling stack too.

although this truck has only ever towed a 30' travel trailer a couple times since then and not had a hard life, I have noticed that for me, it's not "safe" to keep a factory 195 degree thermostat installed, while driving at freeway speeds the temp will easily climb slowly up around 205ish (factory gauge) and I recall a few times seeing temps exceed 210. when the engine is well heated from driving, I can rev the engine up to around 2500 and hold it even with the fan roaring I can watch the temp gauge begin to climb from where it sits normally at just below 200 to just below 210, let off the pedal and let idle, the temp will fall almost instantly. this truck does have the single thermostat crossover with the block-off. My theory has always been that the coolant is being pushed so fast that it's not cooling down even with the overgrown leaf blower driveway clearer 9000 fan under the hood. After replacing the thermostat twice with the same results, I went back and swapped itt out for a 180 degree, this issue was roughly fixed with a band-aid. to add to this, I do have an electric temp gauge with the sensor in the passenger head near the #8 cylinder and it also shows this, but stays with the same reading I get in the dash gauge, so temps across both heads are equal.

Now on the other hand my 93 still has all factory parts, original to 93 water pump, fan, clutch and 195 thermostat. this truck does not do this at all and maintains a steady temp just below 200 at all times other than when I let it become low on coolant (has a slow leak on the timing cover to the block)

Maybe my experience with the differences of a HO pump with a single stat crossover will help

 

[ak diesel driver]

Not all HO pumps are the balanced flow. Some rigs just run hotter than others