• NAXJA is having its 18th annual March Membership Drive!!!
    Everyone who joins or renews during March will be entered into a drawing!
    More Information - Join/Renew
  • Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Not Your Average Cooling System Problem

sandfreestyle

NAXJA Forum User
Location
Charlotte, NC
Begging for help! I’ve been trouble shooting this cooling problem for months and I just can’t figure it out. I've read countless thread on multiple forums, read repair manuals, read the FSM, laser temp check everything, still can't figure it out

Installed a new 4.7 stroker about a year ago and since then I have been having a very odd cooling system gremlin. When I first start up the car it gets to about 195-200* and it will hold there for about 5 min/miles then it will creep to 210* for another 5min/miles and then start creeping to 225*. It holds there while driving but when start/stop traffic happens it will just slowly creep up. Even with the electric fan it will only hold at that temp or very slowly creep. I can’t figure out why this is happening. Please help me!!!

94 XJ with 4.7 stroker w/ about 1,500ish miles (mainly freeway easy driving)
New 180* t-stat
New temps sensors (t-stat housing and back of block, both reading within spec)
New high-flow water pump
New upper and lower re-enforced hoses
New aluminum 3-row radiator
16psi cap
ZJ fan clutch (working properly via drag when cold and stops spinning when shut-off hot)
97+ aux fan
60/40 coolant mix
Timing is dead on
14.5-14.8 AFR (on the smog rollers)
26lbs injectors @ 50psi (per builder’s specs)
91 octane fuel only
 
Well, I have no useful input other than you may want to report in Modified Tech since you have a stroker.

Good Luck
 
My first question would be about your technical aspects of your build. Next would be to ditch the 180* t-stat. Who's water pump? After that the injectors seem heavy. Last of all you shouldn't need 91 octane. The rest would be the proper function of everything!
 
9.8:1 compression so it needs 91 octane
FlowKooler pump
Always ran a 180* t-stat even before the build
Injectors are what the builder (Russ Pottenger) recommends since this engine is 280-300hp. (LS1 valves, custom 1.65 roller rockers, ported head and manifold, blah blah blah) He's built many with the same specs and says those are what the engine likes. I have 30lbs but it's to much fuel and trips codes.
 
I 2nd ditching the 180* t-stat. There is no good reason to run a lower t-stat. The 4.0 operating temperature is 195-215. The t-stat's job is to close the cooling system in order to get the engine to operating temp asap. A 180* t-stat is only opening the cooling system sooner, delaying the engine from reaching operating temp asap, and prolonging the ECU's closed loop program waiting for the engine to reach operating temp. There is absolutely no gain.



What brand of radiator?

Your symptoms sound like inadequate cooling efficiency under load which is either blocked passages in the radiator (perform a full chemical flush of the system), or the radiator is just not sufficient for your engine build.
 
I have a Russ big valve motor! What cam do you have? What's your cam timing? I've never heard much good about the Flowkooler pumps. What exhaust system are you running? Have you had the distributor on a machine?
 
I have a Russ big valve motor! What cam do you have? What's your cam timing? I've never heard much good about the Flowkooler pumps. What exhaust system are you running? Have you had the distributor on a machine?

CompCams (have to check the number) that Russ timed. He built the whole motor himself.
Banks header into a custom 2.25 exhaust
Never had the distributor on a machine
 
CompCams (have to check the number)
Never had the distributor on a machine

Cam specs are important.....
That distributor should be "tuned", but what does "Zero" mean, at idle I run about 10-13*!
 
Also, have you ported the t-stat housing so you don't get cavitation?
 
Sorry, it's been a couple of decades since I owned a OBD I or a Renix XJ!
 
Cam specs are important.....
That distributor should be "tuned", but what does "Zero" mean, at idle I run about 10-13*!

With a "normal" cam you should have higher vacuum than this. Depending on the duration and overlap, it can be lower.

Double check that there is no exhaust restriction.

Work on making sure you don't have an air bubble in the head.

Check that the lower radiator hose isn't collapsing as it warms up.

Pull the spark plugs and do a reading (post up the pix)

Personally I run an AFR on my stroker. I found that the Renix ECU can have issues sometimes and cause either very rich or very lean running. I have a map adjuster and moving it too much really screws things up.
 
Last edited:
As others have said, I agree with the use of an on-board AFR and Mopar 195* stat. I had similar cooling problems with overheating several times especially when stuck in traffic on hot days, causing me to pull over and park it until it cooled down My rig is a 91 MJ with a 4.6 Hesco stroker engine, Mopar Performance header, new 5-port injectors, bored throttle body, 2.5" dual exhaust, etc. It also has a Hesco high flow water pump. Tried most everything in the cooling system to stabilize the temps, like a new FFD 2-row aluminum radiator, cowl hood, etc. What finally worked was this: http://gojeep.willyshotrod.com/HowtoRadiatorRestrictor.htm, Gojeep's radiator restrictor mod. It's a simple disc placed in the upper radiator hose with a hole in the middle. I tried several sizes and ended up using one with a 5/8" hole. How and why it works is all explained on his web site. It's definitely worth a try since it's easy to do and costs very little.

Restrictor6.jpg
 
I have almost exactly the same motor but it’s 2.5 exhaust and lower compression with boosted tech supercharger. I have the exact same issues almost. I get a little more than 5-10 minutes before it really starts creeping but not much longer.

I can’t really keep it cool on highway or sitting still. I’m bored .030 over so not to far there I wouldn’t think.

I have 3 row aluminum eBay radiator, Zjfan clutch, stock water pump, trans cooler removed from radiator and in a Hayden cooler, I bored out my thermostat housing, 195 degree Robert Shaw thermostat.

-I am now purchasing a new ac condenser as mine is a little big rough.
-new Novak 2.5” 2 core aluminum radiator. Best I could find anywhere. 💰💰💰
-new flowcooler waterpump which I think I’ll hold off on installing.

Hopefully this combination does the trick it will be a couple months before I get to try it out. Which by then it will be cool outside again and I’ll likely not have any issues.


Sent from my iPhone using Tapatalk
 
Cam is a 68-232-4

I did the upper hose restrictor in 1/2, 5/8/, and 3/4 with no help at all

I tried "burping" the head by pulling the temp sender in the head while on a steep hill, even dropped on air in the front tires. Was at about 30* butt high when done.

Lower hose is not collapsed at all.

I'd have to get a pic of the plugs, but I've tried normal Champions, Champion Iridium, E3, colder Champions and with same results.

Tried fuel pressures at 39, 50, and 58 psi on the rail.

Even modified an aux fan to housing a Taurus motor with the Jeep blade. (surprisingly easy mod)
 
Have you pressure tested the cooling system? Might not be holding, never had any luck with alum aftermarket rads. Always seemed to leak at the tube/tank and lose pressure. Smallest of leak would cause mine to get hot but wouldn't drop the coolant level much at all.
 
I went ahead and swapped a stock pump I had on the shelf and a cheap CSF 1-row rad just to test and everything is working the way it should now. Hasn't gotten over 215 after a good long test drive with start and stops at the end. Now I'm wondering if the 4-row rad will have any difference with the stock pump.
 
Back
Top