My 2004 SR5 with 271k has been losing coolant. NO drips, no fog from tailpipe, no lost power. But, the reservoir level keeps dropping. Am i looking at a bad head gasket? If so, what does that normally run to have done? I have one of those kits to detect a bad gasket via the radiator water, but i wanted some feedback. Thx.

Assuming you have no leaks you could have a bad head gasket. I would confirm that for sure regardless. You can try the kit you have but many folks, including myself, used a similar kit but got a negative result which implied that the gasket was still good. I found my leak on cylinders #6 and #4 by pressurizing the cooling system and using a borescope to inspect the cylinders for any leaks.

Repair price can vary as there a lot of variables. E.g., Changing head gasket and resealing motor only, or adding additional things like timing components, water pump, head work, etc.

In 2022 I received quotes from $4500 - $5500 from dealerships. That was only to replace the head gaskets and did not include anything else. Btw, my truck was running fine with no codes or start up issues. All I had was mysterious coolant loss.

The gas via coolant testers are ok, but I also have trouble with them.

Pressurize the system and confirm. That's the best 1st step after inspection to look for any source of coolant loss. You can rent one from the parts stores.

The borescope is a nice little add on there. You could also listen for any hissing

Do you ever smell coolant when walking by the front of your vehicle? Do make sure you are not losing it somewhere. These radiators can seep out the seals when they get old. You can pull off the plastic cover on top of the rad and look down all the sides looking for pink bubbly looking seepage. I just replaced my radiator because of the issue. It never leaked enough to have drips on the ground but I could smell the coolant at times.

Hopefully it's this sort of issue and not a HG.

Thanks for the feedback. I never noticed any leaks and i changed the Radiator a year or so ago. It's been losing coolant for a while with no obvious smoking, rough cold starts or anything.
My truck has a total loss title due to hail damage. I've had it from new and planned to repaint it this summer. I love this truck.
But, big dollars to repair it doesn't make sense. I'm seriously thinking of trying Barr's leak or equivalent to see if I can get another year or two out of it. I"ve seen multiple reviews about its effectiveness and if i have the leak, if the block test is positive, it's probably minor and this stuff may do the trick.
Thots?

I had a mysterious coolant leak around 60k miles on my 2006 v8, but I purchased it at 52k in 2019...time leads to old gasket problems regardless of miles I guess. I eventually found the seal for the water pump was bad, barely visible just under the throttle body. After the water pump was replaced, no more missing coolant.

No, don't add that stuff.

Just rent the pressure tester and inspect the entire cooling system. There are several other places you can have a leak from, so try that first. Diagnose first, then fix or at least evaluate what it would take to fix.

Change the radiator cap if you did not do so when you put in the new radiator. Perhaps the problem - cheap & easy.

I think i've dodge a bullet. I did the block test and it was negative. Upon closer inspection I noticed that pink crusty debri around where the upper rad hose connects to the radiator. I tightened the clamp and cleaned it off to see if it reforms. Hopefully that's it. But the clamp was pretty tight to begin with, so ii'm wondering what could make it seep there. Anyway, I'll keep everyone posted. Thanks again. Fingers crossed.