So I bought another set of running boards two weeks ago, and they came with a free '01 140k D2! Slight overheat issue, well, pretty severe actually. I bought it to part it but in the course of staring at it in my driveway for a few days I couldn't help but poke at a few things. Here's the chain of events.

A) Ran the truck for 30 seconds to drive it onto the flatbed and it left a pancake sized puddle of coolant on the deck of the truck. When I got home I pressurized the cooling system and discovered that the hose nipple next to the CTS wasn't secure and was hissing. PO used an oversized piece of fuel line when he did a TBH delete and it wasn't sealing. I replaced it with a proper hose and it stopped leaking, and held 10 PSI for over an hour, yet boiled over after about 10 minutes of running.

B) I noticed the upper radiator hose wasn't getting hot as it boiled over so I threw a different factory thermostat in there. Upper hose now gets hot, still boiled over.

C) The lower radiator hose wasn't getting hot either so I swapped in a known good Nissens radiator. I noticed a ton of aluminum flakes in the system (Alumiseal presumably) so I flushed the block before installing the Nissens but it still overheats. Now I'm running straight distilled water in it. Side note: I noticed the lower radiator hose wasn't getting hot in one of my other trucks in the driveway which was cycling between 183° and 176° for about 10 minutes either.

D) I found that that either when the PO did the TBH delete with the oversized fuel line, or when they replaced the overlow bottle with a new one, they connected the nipple next to the CTS to the nipple in the neck of the overflow bottle. And the small hose coming from the top of the radiator was connected to the bottom port of the overflow bottle, which was backwards. I reversed these connections back to their proper homes and yet it still boiled over once again.

E) I replaced the HD fan clutch and HD fan with the stock units out of my daily but no change to the overheat.

I assume that in an attempt to solve the overheat the PO replaced the water pump, the overflow bottle, both new, and jumped out the heater core (hopefully before the Alumiseal). I corrected all that other crap, each time thinking I had found a smoking gun but nope. Each time it slowly climbs up through 210 and if the cap is loose it boils over. Coolant is flowing into the overflow bottle at a pretty good clip so I assume the water pump is good, and the cooling system still holds 10 PSI for a minimum of an hour/hour and a half (that's the longest I've tested it). There is no smell of coolant in the overflow bottle (no actual test performed) and there's no crossover between the oil and coolant anywhere.

Today I did what I swore I wasn't going to do and I pulled all the plugs to check compression. 6 of the cylinders were spot on 170PSI, second from the back on the pass side was 155PSI (didn't retest) and the fire wall cylinder on the driver's side was 180PSI.

Any thoughts?

 

 

Have you don't a coolant gas test? That'll tell you immediately if you have a blown HG leaking exhaust gases into the cooling system. On really bad ones the reservoir will usually smell of exhaust/fuel.