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Old July 16th, 2019, 11:40
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NXJ4CB NXJ4CB is offline
NAXJA Forum User
Join Date: Oct 2007
Location: San Diego
Posts: 12
Re: Overheating solved

Hello again,

I think this theory might only apply to those who have installed (non-stock) high flow thermostat housings, high flow pumps and maybe aftermarket radiators in that order.

The reason I have my setup is one day shortly after lifting my jeep I saw a high temp to me of 215 or so. Before that, the needle never budged. Ever. I thought it was time to squash that, so I put in all the "upgrade" parts I could find all at the same time and was really upset when it started to run even hotter after that.

I assumed that any upgraded part was better as they are advertised to be. For years I could not wrap my head around the possibility that it was those very parts causing the higher temps. Multiple troubleshooting replacements of the same upgraded parts produced the same results. Here's a short list:
3 high flow pumps, 1st Hesco= failed, 2nd=Flowkooler failed, all leaks.

2 CSF 3 row radiators, none failed.

Multiple thermostats, including Robert Shaw, various temps.

Engine rebuilt, head verified good, but it's the 0331.
2 high flow thermostat housings.
1 aftermarket stock aux fan, they're terrible. I replaced that with the Mopar fan, they work better.
Added that Spal fan with no change.

I've been chewing on this all night and I think its those high flow parts creating an environment where most of the flow is just recirculating through heater core and not moving fluid through the radiator much. There are two parallel paths of flow and the design changes of the thermostat housing and or the waterpump create these problems, diverting too much flow through the heater not being cooled at all unless the cabin fan is running.

It's a simple test to perform even with hose clamp pliers like Ehall said in one reply. Here is a link to a hose restrictor and the description deals directly with this theory:

I'm driving my commute today and will update this thread as I test and verify solutions that I try and report running temps as well.

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