New HO waterpump without dual therms upgrade..

[j_k_auto]

Well I just did it. Drilled four 7/64th holes in the flange of my stock thermostat

Where did you drill the holes and why did you decide on that hole size?

[joescj5]

Where did you drill the holes and why did you decide on that hole size?

I drilled the holes on the mounting flange right up against the swell of the T-stat. The holes are evenly spaced around the perimeter. I went with 7/64th as they were almost the largest size I could actually use. There is just not a lot space around the perimeter of the T-stat. Basically there is very limited flat space that you can drill into, but I think there will be plenty of flow to prevent the block heater from being popped out by the new pump.

I only went with four holes because I still want some functionality out of the T-stat. I can always add more holes to increase flow, but the main point of them is to decrease block pressure before the T-stat opens. I was going to take pics, but by the time I got to that stage it was almost midnight, and I was kinda tired. We'll see how it does in an hour or so.

[j_k_auto]

You might of found a way for the single stats to actually work without the pressure build up. I am thinking on going either way at this point. I am tring to decide what is going to work best impo. I do have my crossover out and apart on my bench. I keep looking at it and thinking what would work best.
I am just tring to look at the flow pattern and tring to figure out why there will be extra pressure. I searched this for 6 months and now I can see first hand the difference detween the single and duel setup then maybe I can figure out what will be the right thing to do with the h o pump.

[joescj5]

We'll I don't know if this was the right way to do this or not yet, but it seems to be working pretty well right now. @75mph and normal freeway driving the temp gauge reads 185-190 deg. I started at the bottom of Horshoe Bend hill (6% grade, 7 miles) at 65mph. About halfway up the temp was at about 195-200 deg. I then romped on the accelerator and at the top of the hill the temp was 200-205 deg at 70mph.

This is easily 15 deg cooler than the last trip up the hill. In fact last trip up the temp hit about 220, the SES light came on and I lost all power (Set DTC 78 - Turbo Wastegate Solenoid Fault). Max speed was then 45mph until I crested the hill and the engine cooled.

Ambient temp this trip was about 65 deg, no load other than three adults, a 30lb rat dog, and 60lb Husky. So far this is a vast improvement. I'll post up if any problems rear up.

[j_k_auto]

joescj5 why don't your pm's work? I was wondering where you are located?

thanks joe

[rameye]

I'm running HO pump on single stat... I removed the bypass blocker off the thermostat..

Results so far indicate...

Definite inprovement, however I wouldnt run out and change my rig for the improvement i got unless I really needed some lower temps badly.

The real noticeable improvement was when I had the bypass blocker on the thermostat...the gage would barely move as I climbed hills, of course I wimped out with visions of pulling the motor to slam in a new freeze out plug and removed the blocker.

I like the holes in the thermostat idea...is that a factory stat??

[joescj5]

I assume it is the factory or a stock replacement stat. I've only had this thing for about a month, and it has had a lot of miles put on it by previous owners. So I can't be sure it is factory/stock.

I've updated my profile to include location, the lovely Boise, Idaho. I'm not sure why my PM's don't work, heck I can't even find where to access them I'll figure it out eventually. I am a little slow on the uptake, but I am still trainable

[DmaxMaverick]

.....I'm not sure why my PM's don't work, heck I can't even find where to access them I'll figure it out eventually. I am a little slow on the uptake, but I am still trainable

Cool. I'll train ya.

Go to your User CP (link at the top/left header area on every forum page) and enable the PM's. It's in the "Edit Options" link at the left of the User CP page. Go down to " Messaging & Notification", and check all 3 boxes in the "Private Messaging" area. Click "Save Changes" at the bottom of the page, and you're done. There are other settings available in the CP, so have a look around to see what is appealing to you. The PM's are off by default, which is necessary for reasons we don't care to discuss openly.

[GMC Hauler]

Look inside the dual thermostat crossover and the single crossover (early 96 model). There is a built in restrictor plate in the early 96 model. If you grind that plate away, and then go with the non blocker type thermostat, there is no difference in the recirc flow path at all. The thermostat will flow more water with this modified setup when open because of the increased pump head of the high flow pump. It will not flow as much to the radiator as the dual crossover. This setup is safe and will not pop freeze plugs because there is NO difference in the recirc path.

I've heard a few guys say that the thermostat will cycle open and shut rapidally because of the very cool water that was sitting in the radiator now rushing in the block (which is not necessarly good for the thermal stresses on the block). Drilling a small hole in the thermostat plate as a few of you have done keeps the radiator path somewhat warm and reduces thermal shock to the block. I've done this before (not this engine yet).

[Shikaroka]

How do you know if you are getting a HO pump?
If I go to the parts store and get one for a 99 Suburban, is it going to be a higher output version than my current one?

Like this one At Advance Auto Parts

BTW:
What does "Pull-A-Head Design" mean?

[rameye]

HO pumps are conveniently stamped "HO" on the pump casting.

[More Power]

Here's an email I received from GM regarding retrofitting the dual t-stat and hi-cap water pump to earlier 6.5 diesels. I've not found the other email from the GM 6.5 cooling system engineer - yet, but the admonition was basically the same....

The following email came to me from Dan Fuller, who was a Northeast GM regional training instructor, and who was responsible for training dealer techs on the 6.5 systems in the mid to late 90's.

Date: Wed, 19 Aug 1998

Hi Jim,

If you use the GMT800 water pump on your 94, just make sure that you use the entire cooling system, crossover included. If not, the higher flow pump will create excess pressure in the system due to the restriction of the crossover. This also creates some tricky fabrication as the AC compressor and alternator were swapped to allow rear entry of the upper radiator hose. Let me know how you make out.

The purpose of the dual thermostat housing - more flow... Please caution readers about not removing the thermostat completely - I've had people try this already. The coolant flows through the engine with no restriction whatsoever and travels too quickly too absorb enough heat. Hence, the coolant is not all that hot but the engine metal overheats!

Dan Fuller

[j_k_auto]

Is there a number for him? I would love to talk to him about this and get some updated info.

[More Power]

His personal phone number that I have on file is over 9 years old. Do a google search. I found him in about 30 seconds. I doubt there are too many Dan Fullers involved with GM service training..... It appears he still worked for GM as of December 2006 - and may yet.

Jim

BTW - the 1999 GMT-800 HO 6.5 water pump (treaded fan-clutch attachment) is not marked with the letters "HO". But, it does run the same size impeller as the 1997-98 GMT-400 6.5 HO pump - as measured by my dial caliper.

[j_k_auto]

Ok I found a way to contact him but I will have to call gm and do the run around till I reach him. I will have to wait till monday and go from there.
thanks for the imput on the pump.

[ttyR2]

My understanding is that thermostats also cause restriction that help build pressure in the heads, enabling the coolant to "scrub" localised boiling spots. I think I read such in an article by a tech from Stewart Components a number of years ago.

If that's the case, it's not just about flow, but creating pressure in the heads as well.

[tomtaylor]

If we are just trying to dump excess pressure created by the high output water pump from a closed circuit (that's before stat opens) then couldn't we just create a half inch circuit from the engine back to the rad with an inline pressure relief ball check valve rated for say 12-14psi or whatever the correct psi would be to prevent blowing plugs or gaskets or whatever else???

This allows only the minimum water through to correct the pressure problem would but still allow a better warm up cycle. Once pressure drop the circuit dies until it builds again and then once the stats open the circuit dies until the stat closes again. What would be the correct system pressure to prevent anything from blowing with stats closed? would it be 13-14-15 psi? Are people getting higher than this beofre frost plugs go? need to know where to set the pressure relief valve at?

The guy that was blowing his rad tanks maybe had a compression leak too? Seems odd that a pump would blow a several new rad tanks, but I guess anything could happen when dealling with so many variables.