HMMWV coolant crossover tube install and temp readings..........

[welpro222]

I have a Prestone Robertshaw 190 in my 6.2 with a autometer electric sender tapped into the crossover near the drivers head port. It reads a steady 190 on the gauge. I heard the robertshaws are the best thermostat for these engines. Look for the prestone brand, it says robertshaw on the box. You can get it in 180 or 190, its made for the coolant crossover with the bypass block. It fits in the older no bypass block crossover just fine. I have this thermostat in two of my rigs and they hold a steady temp.

 

[Drock]

If you come to a complete stop and your temp drop you could be low in antifreeze.

Well as it turns out you may have bin on to something. When I did the crossover swap I also replaced the heater hoses. The problem is I eyeballed the size of them as 3/4". As it turns out only one is 3/4" and the other, along with the bypass hose are 5/8"but I just put the 3/4"s on anyway. When I started the truck yesterday morning for the first time I did ah quick check under the hood and saw that the hose on the 5/8" side of the heater core was leaking down the firewall. But as soon as the truck warmed up and the system built pressure the leak stopped. So I should be getting the new thermostat in the mail today and I'll swap out that 3/4" hose with the 5/8" it's supposed to be. I'll report back with the results.

 

[Drock]

So the other day I replaced the 3/4" heater hose with the correct 5/8". Then installed the new thermostat #14077122, which is a 190° acdelco unit (from the dealership). Then poured in another bottle of water wetter. Today I drove a 150 mile trip. 75 of which I had 1000LBS of steel in the bed. The temp never got over 192°. When I got back I checked the old thermostat (also a 190°) and it would open slightly at 195° and stick, only closing after tapping it. So moral the story replace the 30 year old thermostat whether you think it needs it or not

 

[R Racing]

Well as it turns out you may have bin on to something. When I did the crossover swap I also replaced the heater hoses. The problem is I eyeballed the size of them as 3/4". As it turns out only one is 3/4" and the other, along with the bypass hose are 5/8"but I just put the 3/4"s on anyway. When I started the truck yesterday morning for the first time I did ah quick check under the hood and saw that the hose on the 5/8" side of the heater core was leaking down the firewall. But as soon as the truck warmed up and the system built pressure the leak stopped. So I should be getting the new thermostat in the mail today and I'll swap out that 3/4" hose with the 5/8" it's supposed to be. I'll report back with the results.

I have had issues in the past that led me down that road. I'm glad you got it fixed !