So, a few months ago I got a low mileage 1990 D250 with a Cummins and auto transmission. I haven't driven it much until recently and I started to notice some odd cooling system behavior.
Under normal driving, the temp gauge sits on the 2nd mark in the normal range, as shown in the picture below.
That's probably fine, but when the truck is coming up to temp, it overshoots that mark by 1/2-3/4 of a section (needle sits straight down or slightly hotter) and then it looks like the coolant starts flowing to the radiator all of a sudden and it gets cold again (almost coming down to the 1st mark) within a few seconds. I noticed it was also spraying coolant out of the overflow tank, though somehow the radiator was staying full.
Great - I figured it was a sticking thermostat, so I pulled it apart to replace it and I found this sitting inside the upper radiator hose...
The PO had a new radiator put in at some point and that was capping the inlet - it wasn't removed before the install, the upper hose was just clamped over it. Anyways, I also pulled the lower and didn't find anything on the radiator outlet or in the lower hose. Threw the new thermostat in and drove it to work today - it's doing the same thing (though it didn't spray any coolant out of the overflow).
I'm wondering a couple things:
1) any thoughts on the coolant getting hotter than normal and then coming down in temp quickly?
2) if there was a cap on the radiator outlet and it got sucked into the motor...how the would you go about looking for it? I'm really nervous that it got sucked into the motor and could possibly be blocking something. I've ordered a water pump and new hoses and am planning on pulling the radiator out and taking care of the KDP anyways, so I can go poking around some more.