Thermostat Bypass Blocker?

[bowtiebutler956]

What is 12559338 for then? A double t-stat housing?

The 12559338 is a 190 for the single thermostat 6.5's, just like I have pictured above. Its not a 195, it says 88 Celsius on it, which is 190.

Matt

 

[bowtiebutler956]

So the double housing has one stat with a blocker on the bottom and one without?

No, the dual thermostats don't have the blocker on either of them. I believe they use a restriction in the bypass to compensate.

Matt

 

[THEFERMANATOR]

No, the dual thermostats don't have the blocker on either of them. I believe they use a restriction in the bypass to compensate.

Matt

gms idea was the dual stats flowed enough that they didnt need a bypass blocker. It has been found that they needed restrictor to help get full rad flow. This is why heath reccomends the single now, and sells a restrictor for the duals. Gm added a blocker when they made the duramax as they had learned there lesson from the 6.5.

 

[bowtiebutler956]

I already updated the build thread on the truck, but I thought I'd post this here as well, since it seems relevant.

I installed the new 9 blade fan with the modded clutch today. I wasn't very impressed with the look of my new fan clutch when comparing to the factory unit. The factory one is both wider, and thicker. However, once it was installed, I couldn't tell it was smaller by the way it pushes the air! This thing doesn't seem to ever fully disengage, but when the trucks cooler, it is quieter. If you leave it idling with the AC running for awhile, it sounds like an airplane taking off when you leave, and stays that way for a short period of time before quieting back down. I don't mind hearing the sound of my fan, so I'm very happy so far, and will post more updates after I've taken it for a long drive with a loaded trailer. Here is a video, as well as some pics for comparison between the fans. Thanks

Matt

https://www.youtube.com/watch?v=THYasPSlA14&feature=youtu.be

 

[dangerousdave]

Thanks, Matt.

 

[JayTheCPA]

gms idea was the dual stats flowed enough that they didnt need a bypass blocker. It has been found that they needed restrictor to help get full rad flow. This is why heath reccomends the single now, and sells a restrictor for the duals. Gm added a blocker when they made the duramax as they had learned there lesson from the 6.5.

I was a little curious as to the differences from single to dual blocking. Any threads out there on how to do it for a dual setup?

 

[HotRod77]

Has anyone found a good restricted thermostat for the dual tstat system? Is the duramax dual the same as the 6.5? Any suggestions.

 

[JayTheCPA]

Will need to add a restriction in the bypass port off the water pump as opposed to a thermostat with a built-in bypass blocker. Here is a pic / reference for adding a restriction: http://www.thetruckstop.us/forum/threads/a-military-rebuilt-6-5.43832/page-33#post-502585

In terms of thermostats, I just installed Mr Gasket 195*'s and am liking them so far. Just look on Summit and there is only one 195*F part from Mr Gasket.


And to balance out the cooling package, consider a Hayden 2886 fan clutch.

 

[FellowTraveler]

Has anyone found a good restricted thermostat for the dual tstat system? Is the duramax dual the same as the 6.5? Any suggestions.

The housing design for the dual does not allow for bypass blocking thermostats, it requires higher flow stats installing lower flow stats could come back and bite you in the a__. The dual system requires a restricter in in the bypass hose to get the most from the cooling system. As a single thermostat housing goes I've not seen any that meets the flow requirements of the newer HO pumps, I had asked if there is a difference in their design to allow for more flow never got an clear answer.

 

[FellowTraveler]

Yes, there is a part missing. Rubber mud flaps cut up do wonders there...

Yep that missing tab directs flow up to cooling stack GMT400 that had HD towing had tabs on both sides to direct the air from the bumper holes upwards.

 

[WarWagon]

The housing design for the dual does not allow for bypass blocking thermostats, it requires higher flow stats installing lower flow stats could come back and bite you in the a__. The dual system requires a restricter in in the bypass hose to get the most from the cooling system. As a single thermostat housing goes I've not seen any that meets the flow requirements of the newer HO pumps, I had asked if there is a difference in their design to allow for more flow never got an clear answer.

There is a clear answer and it it that it takes the two thermostats to get the highest flow. And you still have to restrict the bypass to cover GM ongoing cooling system screw ups. Further there are concerns of higher block pressure with a single t-stat and a HO water pump pushing out freeze plugs.

In my experience running a single T-stat and a HO pump the Single T-stat was just fine. Extended high RPM means my freeze plugs were very tight... Really concerned - run a lower pressure cap. 14 PSI or make sure you get a 15, not 16 PSI cap the parts stores hand you all the time. The water pump just doesn't generate that much pressure. EVANS 0 PSI coolant is a option.

Only when I went really crazy with the spool valve did I reach the limit of a single T-stat in AZ 121 degree weather. Spool valve traps more heat in the engine. With a better turbo the cooling needs are less. Even so running a GM3 hard the single t-stat worked fine with a KD low temp fan clutch.

Again the clear answer is there isn't a need for the dual t-stat setup unless you are building more power than 99% of us. I can think of 3 members would would benefit form this and that doesn't include me as I sold the 1995 that would have. It's now in a colder climate and doesn't need it now I expect.

 

[FellowTraveler]

There is a clear answer and it it that it takes the two thermostats to get the highest flow. And you still have to restrict the bypass to cover GM ongoing cooling system screw ups. Further there are concerns of higher block pressure with a single t-stat and a HO water pump pushing out freeze plugs.

In my experience running a single T-stat and a HO pump the Single T-stat was just fine. Extended high RPM means my freeze plugs were very tight... Really concerned - run a lower pressure cap. 14 PSI or make sure you get a 15, not 16 PSI cap the parts stores hand you all the time. The water pump just doesn't generate that much pressure. EVANS 0 PSI coolant is a option.

Only when I went really crazy with the spool valve did I reach the limit of a single T-stat in AZ 121 degree weather. Spool valve traps more heat in the engine. With a better turbo the cooling needs are less. Even so running a GM3 hard the single t-stat worked fine with a KD low temp fan clutch.

Again the clear answer is there isn't a need for the dual t-stat setup unless you are building more power than 99% of us. I can think of 3 members would would benefit form this and that doesn't include me as I sold the 1995 that would have. It's now in a colder climate and doesn't need it now I expect.

Thanks for the reply good info.

 

[Burning oil]

I wanted to run a single on the 96 and had one bolted on ready to go. Ran into a problem in that with a DB2 the throttle bracket was in the way. Had to go back to my old set up were I used a dual with the neck turned upside down.

 

[Will L.]

Im trying to figure a better one to run with the van manifold and a db2. Getting close to doing some fab work and going with inline thermostat instead.

 

[WarWagon]

I wanted to run a single on the 96 and had one bolted on ready to go. Ran into a problem in that with a DB2 the throttle bracket was in the way. Had to go back to my old set up were I used a dual with the neck turned upside down.

Was there a different single than the 1992/1993 years have as this clears the throttle and cruise brackets on the DB2's.

 

[ak diesel driver]

I sold him one off a 96 which is different than the older ones. Actually kind of rare

 

[Burning oil]

Early 96 tstat housing/crossovers were single and clears a/c on 96-2000. It uses the same tstat as 92-95.