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

[dbrannon79]

Not sure how reliable the PMD is but I have heard of this brand online before. The truck vin I got it all from is 1GBHC39F2RE221459

 

[dbrannon79]

I got the idea about cleaning the coolant bottle from this youtube video. not sure how it will work but I will find out soon enough lol.

Edit: aparently you have to open the link in youtube to play it.

 

[Will L.]

@Husker6.5
Ok cool! Good to learn stuff. I thought it was just that driver side leg that had the funky angle.

I am gonna do the cube stye if I can’t fit the single stat I have. That will definitely flow!
Note the date- these prices are really old so probably $200 each by now.

A fellow could easily have them made bigger, or use two for maximum flow. Then just “Y” together to the top radiator hose. Guarantee that would outflow either option.

Note the threaded hole on bottom for the block off output to waterpump return.

 

[Will L.]

@Husker6.5
Or anyone that has a thermostat for the rare 96 here ( @n8in8or don’t you have one or two?)
If you can find the AC Delco numbers for that larger thermostat- then we could measure one up and do the area math. See what percentage flow difference it is from the regular to it, and the duals as well. Be interesting to see.

 

[dbrannon79]

@Will L. I think you and Husker should put togther a thread on the various different housing throughout the different years for these engines in the technical reference library. this would be some good info for everyone

 

[Husker6.5]

@Will L. I think you and Husker should put togther a thread on the various different housing throughout the different years for these engines in the technical reference library. this would be some good info for everyone

Very easy to do. You had the X-over/single t-stat housing with the forward facing outlet used on 1992-1996 6.5's on both V-belt and serpentine engines. Then you had the X-over/dual t-stat housing with the rear facing outlet on the 97 (late 96)+ 6.5's. Special application 6.5's (like some cab/chassis or stepvan) could have a straight up outlet that used a three bolt mounting bolt pattern.

You'll know you have the very, very rare intermediate design large single t-stat, because the X-over stat housing is very squarish, has a large round center well for the t-stat and four bolts, one at each corner of the housing, and exits the same direction as the 97+, but the outlet housing bolts down to the X-over, not to the back of it like the dual t-stat outlet housing does.

 

[J_dude]

Very easy to do. You had the X-over/single t-stat housing with the forward facing outlet used on 1992-1996 6.5's on both V-belt and serpentine engines. Then you had the X-over/dual t-stat housing with the rear facing outlet on the 97 (late 96)+ 6.5's. Special application 6.5's (like some cab/chassis or stepvan) could have a straight up outlet that used a three bolt mounting bolt pattern.

You'll know you have the very, very rare intermediate design large single t-stat, because the X-over stat housing is very squarish, has a large round center well for the t-stat and four bolts, one at each corner of the housing, and exits the same direction as the 97+, but the outlet housing bolts down to the X-over, not to the back of it like the dual t-stat outlet housing does.

What about the one on my 96? X-over/single t-stat with outlet to the rear, the two-bolt outlet housing bolts to the back side of x-over.

As for what I did to mine, well it was yesterday but I swapped the rad back to the style with no cap (someone put the older style in at some point, but it was leaking so I got the “right” one to put back in it), replaced gaskets on my coolant x-over, and flushed my cooling system. Now waiting for a new t-stat to come on Wednesday... darn long weekends lol.

 

[Big T]

What about the X-over on my sons '94? Cover plate faces to the rear. Are we better off going to the dual t-stat X-over (have one)?

 

[J_dude]

What about the X-over on my sons '94? Cover plate faces to the rear. Are we better off going to the dual t-stat X-over (have one)?

That’s a single t-stat like mine? I just watched an old video from LeroyDiesel on YouTube yesterday about the different types and he said the ones like mine outflow the dual housing x-over

 

[Big T]

That’s a single t-stat like mine? I just watched an old video from LeroyDiesel on YouTube yesterday about the different types and he said the ones like mine outflow the dual housing x-over

Well we've done every single cooling mod and the truck still runs to the hot side. Easily hits 200 with no load upon medium acceleration. Go up a grade and it's hitting 210. My '99 with all the cooling mods runs at 187 and only gets above 200 towing up a grade and it has the dual crossover.

 

[ak diesel driver]

If you do the math I believe the duals flow more than the early singles

 

[jrsavoie]

Well we've done every single cooling mod and the truck still runs to the hot side. Easily hits 200 with no load upon medium acceleration. Go up a grade and it's hitting 210. My '99 with all the cooling mods runs at 187 and only gets above 200 towing up a grade and it has the dual crossover.

Have you done a cooling system pressure test?

 

[J_dude]

If you do the math I believe the duals flow more than the early singles

But the dual housing is constantly dumping hot coolant straight back into the WP, even with the Bypass Restrictor.

 

[J_dude]

Have you done a cooling system pressure test?

X2. Sounds like something’s not right

 

[Will L.]

The pressure created by the heat far exceeds the pressure differential created by restriction (boyles law). Remember the water pump is an IMPELLER not a positive displacement pump. So flow restriction simply causes cavitation at the source.
The bypass is to alleviate this cavitation.

The main restriction in flow is the thermostat and the units opening is what has to be measured. Any single person could do the physical testing simply by buying one of each thermostat. Lock the stat open and mic the size of the opening, size of the plunger, size of the gap between them.

As to ALL the crossovers - there is also another 6 styles used on hmmwvs and 2 more in hummers- that I have seen. Probably more I haven’t seen. But NONE of them have bypass blocking so I wouldn’t waste my time on any of them. Then there are a couple different ones that were used for generators- but they were the worst of all and recalled. Hopefully all destroyed. The very best one was for a generator. It is a butterfly valve operated by a solenoid controlled by temp sensor.

If I was rich and famous like all you guys, I would replace the waterpump with 2 positive displacement electric pumps, one for each side of engine. Control it with temp sensors for that side of the engine. Zero thermostat. Then as each side of the engine gets hotter or cooler the appropriate water pump cools as needed. And if you want more heat in the cabin is cuts back. Easy peasy lemon squeezy!

But seriously- if anyone want to take the time to measure up different thermostats, make some cool pictures and a big spreadsheet showing all the magic- we could all take some old or spare thermostats- label up what crossover they fit and ship them to you. As much as I actually enjoy doing this kind of weird stuff- there is no way I can add this to my list any time in the next few years.

Sounds easy and complete, right? idk...
There is the argument of flow characteristics through different housings and what happens with or without BRF, how hoses are routed affecting the bypass rate, and how much of an advantage Chris has from coating the inside of his housing! Haha.

Seriously, I have a few stats I can send if someone has a set of calipers and some time...

 

[Will L.]

X2. Sounds like something’s not right

@Big T i know you covered stuff across multiple threads, and with the son having it you can’t play with it as easy.
But this is where having a dedicated thread to a real problem child comes into play.
Do you have one on it to bring up again and we can recap all details to see what’s happening? If not, collect all the details and start one. Include in the title “NO DERAILING THIS THREAD!” so it stays focused and solves this issue. Your son and grandkids travel in areas where breaking down could be really bad. Let’s solve this issue.

 

[Big T]

@Big T i know you covered stuff across multiple threads, and with the son having it you can’t play with it as easy.
But this is where having a dedicated thread to a real problem child comes into play.
Do you have one on it to bring up again and we can recap all details to see what’s happening? If not, collect all the details and start one. Include in the title “NO DERAILING THIS THREAD!” so it stays focused and solves this issue. Your son and grandkids travel in areas where breaking down could be really bad. Let’s solve this issue.

I'm in Fullerton for 5 more weeks and the Suburban is in my driveway. Son says he's been driving it and it's running good, but has a fuel leak. That's on me as I disconnected the clear return line for some test and forgot to reconnect it and made a run to the local Walmart, dumping fuel everywhere. I need to go through it to make sure everything is tightened up.

Next thing on this list to remove the stamped steel lower control arms and replace with the forged control arms with new ball joints and Energy Suspension bushings. I will probably have to cut the existing control arms off the torsion bars as nature's weld prevented their removal the last time I tried.

Then I can get on the finer points of addressing engine coolant temps. Or repairing the arm rest that has broken off the inside driver's door. Still proud of the door work I just did on the '99 up in Montana.

Also need to find a clean hood in a pick a part boneyard for the '99. Plan to strip, paint and replace the one on the '99. Want to do it on a replacement hood, so I don't lose the ability to drive the truck while doing this work. $70 for a clean hood is reasonable.

 

[Will L.]

On your trips past this way- call ahead of time to the junkyards in Vegas. Tons of non rusted trucks, some they pull the parts and store them ahead of time like a parts store. Could be worth the extra couple hours drive time.

 

[Husker6.5]

If you do the math I believe the duals flow more than the early singles

Yes they do. However, the rare '96 transitional large single t-stat X-over does out flow the later dual t-stat version. But the large single is like hen's teeth to find. The dual is plentiful and a vast improvement in flow over the early single design.

 

[J_dude]

Yes they do. However, the rare '96 transitional large single t-stat X-over does out flow the later dual t-stat version. But the large single is like hen's teeth to find. The dual is plentiful and a vast improvement in flow over the early single design.

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?