Blown head gasket or just short driving?

I made the edit above. Lol. In my defense, it’s not like I’m making up this situation, it’s literally happening to me, I just figured it was normal. I dunno.

 

No worries man. All we want is the right info to get out there. Based on all the cars I’ve had I’ve never seen a suck in like your condition. The laws of thermodynamics is the same whether its 1.6L or 5.7L.

Basically, in proper fashion your coolant in rez should be like these tests/pics just posted. Stay the same when cold and rise when hot.

You need a good baseline start which has been mentioned earlier in a few posts. You probably are low in the rad. Fill rad when cold to the top. Run it to hot and then top of the rez to the Full line. This is your new baseline.

 

Question: could the fluctuations in coolant levels depend on whether or not a truck is outfitted with a transmission cooler? Or is it a completely different "circuit". If a truck wasn't outfitted with a tow package, I don't think they came with one. And then they eventually nixed a separate transmission cooler altogether for the later models regardless of tow package.

 

We're just trying to help you avoid huge trouble. You don't need to take it to the dealership...yet.

Your reservoir level in the pic is fine; mark the level with a dot like others have done. As @AZBoatHauler said, now just remove the radiator cap and top off the radiator. Overflow the filler neck if you want. It will hurt absolutely nothing to do that. Replace the radiator cap.

Then, you need to start/drive the truck and warm it up to expand coolant through the overflow line into the reservoir. (Remember @AZBoatHauler pictures from before.) That will eliminate ALL air in your cooling system just like it came new from the San Antonio plant.

When the engine cools, any over-expansion coolant will be drawn back into the radiator without ANY air space. The final level may be slightly different from the mark when it cools because you will have filled the volume of the overflow hose, and it remains filled. (Assumes there are no holes or leaks in the hose; if it leaks, and draws in air, then it needs replacement.)

IF THE RESERVOIR OVERFLOWS and coolant runs out on the ground...THEN take it to the dealership. Tell them the cooling system isn't working properly. It isn't working right if the reservoir overflows from an initial cold level under "FULL" and above "LOW".

 

Anywhere coolant and other fluids are in proximity across an exchanger interface, there is a possibility for cross-exchange of fluids due to exchanger failure.

For Gen2/Gen3 4.6L/5.7L, those possibilities with engine coolant are transmission warmer/cooler mounted on the transmission, and the engine oil cooler (tow package) mounted on the engine front cover. In the first case, transmission fluid can be contaminated by coolant, and in the second, the engine motor oil is contaminated by coolant.

The engine oil cooler was suggested early in this thread, but parts shouldn't be removed to find a suspected leak until you KNOW that there is constant, abnormal coolant loss with no signs of external leakage. Normal coolant attrition due to poor maintenance diligence has to first be eliminated as the cause, and then the leak confirmed and identified if possible before wrenching.