This. There's only one way to max out at 150 degrees, if the sensor is properly positioned. The antifreeze is not being held in the engine long enough to get up to acceptable temps.

 

that's what I think too...

I had a saab that did this. I changed the stat and it did the same thing. You could coast in neutral down hills and gets the temps into 120's I used to do it all the time. it would heat normally while driving but when you wanted to lower the temps going down a hill, just coast. I never could figure it out.
This rover is extreme however...this is better than the inline mod.

 

Brand new 180 degree thermostat, black, from britpart.
I should also note I still get heat inside, albeit not very warm, but it never gets very warm and never has. So for sure, something is still hot. I'm assuming it's just getting the temp from the radiator, and that is remaining closed.

 

New thermos are often bad out of the box. Change your thermo. Better yet, do the online mod and use a motorad 180 thermo for a big block Chevy.

 

Have experienced a new thermostat being bad, too (though, can't say I've experienced it "often"). Never assume that because a part is new that it is functioning properly.

 

I had 2 stants in row bad out of the box. I changed to motorad. Always drop them in boiling water first and make sure they function.

 

I do this with a thermometer to see if they are accurate.

Some stats OPEN at a certain temp, some are fully open by that temp.

 

Now I'm getting a check engine for thermostat defective. So all signs point to bad thermostat out of the box. Already talked to LK8, and a new one is on the way. If this solves it, I'll update you. Thanks all.

 

PO126????

If it was “defective” it would stay closed & you would be running hot. Seriously doubt it’s defective, but at least Lucky8 is sending you another one. However Lucky8 does NOT sell the Britpart 180F thermostat marked at 78C. They sell a generic knock off that comes in bubble wrap. It is supposed to come in a Britpart box.

Your problem is you’ve got to much cold air going thru the radiator, and the thermostat is opening/closing, opening/closing, opening/closing, and opening/closing rapidly. That is why with SAI you’re getting the P0126 fault. Your engine is not reaching warm up temp soon enough.

Either slap in a stock temp thermostat, standard duty fan clutch, or block off “some” airflow.

 

Defective can mean stuck open or stuck closed. I run in the denver area all the time. His temps tell me his thermo is stuck open.

To the OP, spend 80 bucks and do the in line thermo mod. It is easy and you are gonna drain your coolant anyway. That original design with the thermo so far away makes no sense. Make sure to use a motorad 180 for a big block chevy.