No pressure in cooling system

[JHZR2]

My 91 350sd doesn’t lose or consume coolant. But it also doesn’t build pressure. Ive never seen it build pressure in the system.

I have no idea how old the radiator cap is. There’s no residues around it, no signs of moisture or anything around it…

But the system doesn’t build pressure. It works just fine, the needle stays at the upper section of the “8” in the 80 C marking on the gauge. System is clean.

I don’t have concerns on this one about head gaskets or whatnot, it was redone before I bought it from a reputable shop. I kind of woukd prefer keeping it like this, since I run 50/50 anti freeze. But at the same time I don’t want to do harm from cavitation or something due to low pressure…

Or is it that I’m just not running it hard enough? It’s this way after a highway run in 85-90 degree weather…

Thanks!

[rrgrassi]

Get a coolant system pressure pump to put pressure on the system. If it builds pressure and holds, then replace the cap. If it does not, there is a leak somewhere, like with the water pump seal or elsewhere.

[optimusprime]

Buy a new filler cap .