Little background, I have an 08 limited with 135k. I’ve done a couple oil analyses which have been fine, but my latest came back with high potassium and sodium. Blackstone says it’s a coolant leak, which I guess points to head gasket. I had just had my water pump replaced which was leaking, but my coolant level was fine when I left the shop. Few days later, overflow was half empty. I refilled it, and 5 months and 4K miles later it’s been below the full line by a hair or 2 a few times, but the next time I look, it’s back at the full line. So very constant.

I bought a block tester kit, and have done 3 tests. The fluid is noticeably less blue, but not sure if that means I’m still good, or there may be a small problem? I tried sucking in some exhaust from the back, which turned the fluid bright yellow. So the fluid definitely works.

And if I am good, what could be causing coolant in the engine, but no noticeable coolant loss?

Before


After

changing the water pump could have got some residual coolant into the oil which is why it showed up on the oil test.

checking the coolant level needs to be done at teh same temp each time, meaning check it when fully cold or when fully warmed up, the level changes based on engine temp.. when hot it expands, when cool it contracts. & when first filling after the water pump change, it will go lower since its burping out air.

do a search for actual head gasket issues, doesnt sound like you have any of teh common symptoms... & being its an 08 its past the years where it was more common.

I don't see how changing the coolant pump can cause any coolant to combine with engine oil. I would not be surprised if following the pump service, your overflow bottle was drained of some coolant to fill the air gaps that surely developed in the system when changing the pump.

Doesn't the Limited have a v8? If so, it's unusual for those to have defective head gaskets. However, if it overheated even once, then all bets are off.

My limited is a V6. Temp gauge has never moved beyond its normal range.