Re: 4.5L stroker and cooling issues

["Jim Blair" <carnuck@xxxxxxxxxxx>]

 A: The designer of the XJ made it short intentionally because (paraphrasing
his words) "I don't want one of those damn ugly tractor motors in this
truck. The 4 cylinder is plenty strong for anyone!" This discussion was
recently hashed through on the AMC-list and I am cc'ing the list to
ascertain what I'm saying is correct. (I'll let you know) I know my 3 core
GDI kept my truck cool in 110 degree weather.


   From: "Greg Friedman" <greg@xxxxxxxxxxxxxxxxxxxxxx>
Subject: RE: 4.5L stroker and cooling issues


Just one thing to add. There's no magic pill to XJ cooling issues. Forget
high-flow water pumps, thermostat housings, magic formulas, or anything
else. If your XJ isn't cooling appropriately there's something wrong
somewhere. Unfortunately the XJs cooling system is just barely enough to do
the job and whenever something in the system isn't just right then you have
problems under certain conditions. Blocked or restricted radiator tubes are
the most common problem even when the radiator is new or close to it.

I've posted this before, but I'll tell it again for all the newer group
members. The reason the XJs cooling system is so marginal has to do with the
fact that the chassis/body was never designed for a straight six. It was
designed for a 4-banger and a v-6. They found themselves in a bind before
the '87 model year because GM wouldn't increase the allocation of the 2.8L
so that AMC could meet the production needs of such a successful vehicle.
That's when AMC came up with the 4.0L. One of the problems with the longer
motor was what to do about the radiator. The lesser of the evils was to use
the short, wide radiator that we all have. While the total surface area is
comparable to other radiators, the fact that it's so wide makes it a
relatively inefficient heat exchanger. Since the efficiency of heat
exchangers are all about differences in temperature, the long tubes don't
measure up because most of the cooling takes place in say the first half of
the length of the tube. The latter half, the temperature difference isn't so
great so not much additional cooling takes place.

The point of that story is that the radiator is the basis of XJ's cooling
problems and there's no magic pill other than making sure the radiator is
working as well as it is designed to.

Greg