Barry,
I had quite an education on this problem with our 85. Here are some pressure
gauges I made for under $15 from parts at Lowes hardware:
http://neksiwel.20m.com/photo2.html

The first time, I cured this problem by taking the radiator to someone who
could blast it out. These days your best bet is probably a new radiator.
Here is a good test; install the coolant pressure gauge and compare readings
with and without both heaters running full blast. Any difference?  If so the
system is probably not rejecting heat fast enough.

Do not tamper with you pressure caps, you are wasting your time.

The second time I had this problem I also tried the NAPA coolant block leak
detector. It also showed a (false) negative results when I indeed had an
exhaust leak in the coolant. Try the pressure gauge first. Let me know what
you find.

Ken Lewis
http://neksiwel.20m.com/
----- Original Message -----
>
> I have tried using a NAPA coolant block detector, but that came back
> negative when I did it a few months ago (i.e. no combustion gasses in
> the exhaust system).
>
> To the questions:
>
> Has anyone in the list cobbled together a _simple_ coolant system
> pressure indicator?
>
> Without knowing if the system over pressures from the get-go or builds
> pressure  slowly, anyone want to take a a stab at the solution?  I'd
> bite the bullit and would pay to have this thing tested, but I've had
> really bad luck at the local dealer and an independant shop and the
> respected shop is about 1.5 hours away and charges about $100/hr.
>
> I'm about to drill out the spring in one of my pressure caps and let it
> flow to the over flow at atmospheric plus a little pressure.  No, not
> really, but this is becoming a rediculous pain in the tuckus.
>
> Thanks in advance,
>
> bem-stem
>