View Full Version : open or closed system?

July 19th, 2005, 16:36
my dad and i are argueing over my jeeps coolant system. i say that it has an open system and he says it is closed can anyone tell me which it has? i have a 2000 xj with the 4.0 inline 6 any help is appreciated thanks.

July 19th, 2005, 16:41
From 1987-1990, the 4.0L XJ&MJ used a "closed" cooling system, where there is a plastic "surge" or "volume" tank installed as a part of the pressure system. The system's pressure cap is not mounted on the radiator, it is on the volume tank. It is possible to replace the plastic unit with a metal one, but the pressure cap will remain on the volume tank.

From 1991 to the end of production, the XJ (to 2001) and MJ (to 1992) had the more conventional "open" system - the plastic tank is an overflow unit, and the pressure cap has a double vent to allow two-way coolant flow (into the overflow tank when it expands beyond the system's capacity, and back into the system when it cools down.)

With a 2000, you have the "open" system.

And, since this seems to be a topic of much debate - THERE IS NO ADVANTAGE OF ONE SYSTEM OVER THE OTHER. Sorry, but I've beaten this one to death several times over. Besides, if the closed system is so bad, why is it appearing on so many late-model vehicles?

Properly maintained, there is no functional difference between the two. There - I said it. I'll say it over and over, and will say the same thing if asked.

(Sorry, but I had to get that out of my system. A bit of inflamed spleen that required venting...)


July 19th, 2005, 16:45
thanks for the help, that gets me back on the road and won the battle with dad. thanks again


July 19th, 2005, 16:57
OK - but how would that have kept you off the road?

Be careful with "winning battles with Dad" - I have found (and so have my kids!) that "old age and treachery will always defeat youth and enthusiasm..."

Where in Indiana? I grew up in Lafayette, Monticello, and Monon...