Yes I understand just tossing some info out not sure why my 2.5 gets hot fast even after the rebuild.

 

I agree that the stat needs to be checked. That would be my first line of attack but that was already mentioned. Sometimes it's a combination of things.

 

There is a similar thread entitled "3.9 takes forever to warm up".... and the ONE THING mentioned in that thread which has NOT been mentioned in this one is that the heater core MIGHT need to be flushed out. Of course you KNOW what a pain it is to get a heater core out. I will continue to watch this thread with interest because I am having similar problems with my '94 Dakota. The coolant just WILL NOT come up to the proper temperature, no matter what I do. And to my way of thinking once you install a new 195 degree thermostat there is just NO WAY that the coolant should stay at any temperature less than that. Seems that physics and thermodynamics both FAIL when it comes to Dakotas. I am stumped on this one - and I eagerly await the day when someone comes up with a logical scientific explanation for this phenomenon...... FredT

 

Ideologically, clogged heater core would actually cause the engine to warm up faster, at the loss of cabin heat.

The Heater Core receives circulating coolant at all times. Thus, the heater core functions as a miniature radiator at all times. Particularly if the cabin fan is on full speed heat, it could take the engine longer to warm up with a perfectly flowing/functioning heater core. If it's clogged, it will not shed that heat.

OK, now with that said. Our trucks use a 5/8" thermostat bypass hose. When we replaced the water pump on our Duramax LB7 last weekend, it uses a 1/4" thermostat bypass hose (and two thermostats).

The theory I have in mind may be that with the thermostat closed, the radiator is not heated, but when moving, cold air + wind chill is flowing past the block, which is having quite a bit of water circulate through the pump and heater core only. It's not a perfect theory, but I have to wonder is a 5/8" bypass hose is too big.

With that said, I have six 1/16" holes drilled in my 180 thermostat, and it has no problem getting up to temperature and opening. The small holes also help burp the system. I can watch the stat open and close on my OBD2 display - it will creep from 175 to 180 then back to 175 up to 180, and the stat opens, cools off, closes, heats up, and opens again.

 

Bypass hose simply allows coolant to circulate thru the engine when the stat is closed.... So far as I know, the stat is the ONLY path back to the radiator, from the engine.

 

Thanks for all the replys and sorry for the time to answer, didn't bookmark page and couldn't find thread at wrong forum.
So....some progress, bought another 195 stat and hung it in a pan of water and measured temp. Opened at 195, closed at 185. good so far. Replaced again and the needle now climbs up and TOUCHES the 2 in 210. Removed the hoses and flushed the heater core with the garden hose, first backflush was dirty and the flow looked good. Live in NE Ohio and temp has been in the mid 20s to 50's and air at outlets is no better than warm. Still not good heat to melt ice on window. Clutch fan is good. With radiator blocked a bad one would show change, it doesn't. With the rad. blocked I should overheat, no signs of that. Cardboard is between condenser and radiator. If the water pump had ALL the impeller fins dissolved there would be no water movement, and would have overheat in the heads and hopefully that indication on the guage. The upper radiator hose is hot on the bottom of the hose but cooler on the sides and top, there is a distinct difference. Leaky stat? Made in Israel
Going to change steering shaft tomorrow and will continue with the heat saga.

 

I know the full size trucks of that generation were a BEAR to get all the air out of the heater core.......