Still hot on highway. Suggestion needed. Long..
 

Need some advise. I am running out of options. Here is the chain of events.

Winter – Installed 3” lift and 275-65-18 tires, tested the coolant and discovered there was CO2 present. Not loosing coolant so planned on head gasket work once I had the $$

February-April – coolant temps were around 198-203 around town and on the highway

In April-May I had the head gasket, head machined, oil pump rebuilt, water pump, belt and the other associated components replaced. After temps were around 200 in town and 208 on the highway

May-June - Installed the RTE 4”+ lift and 285-75-18 tires, Bajarack and Tactical rover bumper.

July – Had new radiator replaced and the soft spring thermostat installed. After temps were around 195 around town and 221 on the highway

August – Had the coolant temp sensor replaced and the viscous fan clutch. After the temps were 200 around town and 221 on the highway. Pulled the bumper (no bumper) this weekend and the temps are still 200 around town and 221 on the highway.

I allowed a shop to do the engine related install including the recent bleedings of the coolant system as I didn’t trust myself. I did the suspension and brake work. The shop that did the work is now suggesting that it is the tire size change from 275-65-18 to the 285-65-18 that is causing the high temps on the highway. They are offering to pull the smaller setup off one of their D2’s and put them on mine to see if it changes anything. I am not sure I want to go thru this effort. I don’t know how this 1 size in tires can cause this.

I am thinking it must be thermostat or bleed related.

Any suggestions/advise on how to proceed? i am beyond frustrated now.

*** Please dont tell me i should have done it all myself. I didn't have the time to do the HG work.. I did do the suspension work.

Tire size shouldn't do that. BUT in theory, your engine IS now working harder, to go the same speed and also SHOULD be turning slower at the same speed which could contribute.

I would just for the hell of it throw on smaller tires and give it a try.

If it works, you may have to regear... But this just doesn't sound right

Considering all the things that you have done to alleviate the condition and that the temp increase has all happened after the headgasket replacement, I would suspect something with the HG job. Maybe the gaskets they used were make incorrectly restricting coolant flow, or something like that. I'm thinking coolant flow since it apparently doesn't overheat until it's under load (on the highway). Just some thoughts.

Belt route?

Fan blade reversed, or power to electric fan reversed? Paper towel held to grille should hold there, not be blown away.

Antifreeze percentage? Straight antifreeze looks green but does not cool as good as 50/50 mix.

Lower hose collapsing at speed (rpm) and choking water supply (need spring inside)?

Pull hose off the top of the thermostat and check for trash in the metering holes (leg that goes to "T").

Belt routing Matches rave, paper towel sticks to grill.

Not sure about the hose collapsing,

I can check for trash when I bleed it this weekend. ,

First you cannot route the belt wrong on a DII.
Second, its the bumper dude, the OEM bumper was designed to do many many things along with the plastic tray under the engine that just gets in the way.
The bumper not only improves aerodynamics it aids in engine cooling by directing air flow through the radiator.
Thats why you temps changed as soon as you installed the new bumper and that is also why they are the same with no bumper.
If you still have your OEm bumper put it back on and see what happens, I bet your temps drop.
And yes, larger tires and heavy bumper make your truck work harder, working harder also increases engine temps.

I have to say air in system. What spike says kinda makes sense but i have a 6 inch opening in between my lights and have no issues. I say air or junk thermostat also just for thoughts what water pump did you use?

Truck is done. No reason to bleed it anymore..

What do you mean done?

Run around town for a bit, then climb a somewhat steep hill, while still on the incline purge the air from the system via the top hose. Any air in the system should find its way to that spot if you follow those instructions.