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RENIX to HO Overheating problem

Monster3663

Monster3663

NAXJA Forum User
Location
Placitas, NM
I swapped my XJ RENIX engine which ran great with a HO engine out of a wrecked 1996 which ran great. I pretty much just took everything off the RENIX and put it on the HO. The problem it that it overheats on steady grade climbs. I can drive all day crawling and in city slow. I was told by local shop to change my intake and exhaust to the HO setup and it should fix it. That the ports were different. I used exhaust gasket for a 1996 engine. Any thoughts on me needing to change the intake and exhaust?

1990 XJ
35's
4.88s
3 row radiator
Flowkooler water pump
open cooling system
new oxy sensor, new temp sensor
 
I know that the intake ports are different not sure on the exhaust side, but if one is different more than likely both are.
 
Have you checked the fan, or fans? Don't know your setup but if you still have clutch fan are you sure it's working correctly ..sure your getting required air flow through the rad.
 
Yes both fans working fine. Hood is also vented. Electric fan is set on separate switch. Just heats up when on grade or pulling trailer. Doesn't heat up in traffic or going slow. It cools down then.
 
consider a wider row 2 core all aluminum. just an idea. my 3 core all metal CSF just wasnt cutting it with 4.88s and 35s (was worse with 36s) went to an all aluminum 2 core with 1" rows and its been good so far. most 3 cores only run 3/8" rows, and have other issues. just food for thought. I run a 180 t stat, new water pump, and straightened all the fins on the a/c condensor. make sure the lower hose has a spring, and make sure nothing else is blocking flow. it could be your tranny heathing things up actually, do you have an auto with a good tranny cooler?
 
Swapping manifolds isn't gonna "fix" it.

Exhaust ports are identical.

Which water pump did you use?

Still Renix cooling system or converted to open?

If still Renix, get a Napa 703-1396 cap for the bottle.
 
How hot does the guage say?
what does it normally run at?

How much have you driven since the swap? All bubbles puked out?
 
you are running a thermostat correct? running no stat can cause to fast of water flow and cause bad heat transfer. only bring this up because your using a hi flow pump. if the radiator is good (not clogged) and engine is clear (no air pockets or clogged passages) you should re check air flow..a spinning fan does not always indicate its pulling the required cfm of air. also make sure your exhaust system is flowing normal if your running a cat and its clogged that will overheat and engine also. its one of these items ..or bad heat gasket ect... cooling system is really simple "coolant flow and air flow" if one is not up to spec it will fail.
 
Are you 100% positive you've fully bled the cooling system?

Just saying as they (open cooling) aren't exactly burp friendly layouts.
With the upper hose full of air the motor will run cool just tooling around but run hot under load and at stop lights (not ovetheat hot just hotter than norm).
 
Just something to look at if the usual suspects fail to solve the problem. Check and see if the overheating is at all related to the RPM. The motor (program) seems to be set up to get best mileage or burn the leanest in the 2000-2500 range. A lean running motor will heat up.

Check a plug or two hot when the motor is heated up. To get a good true read, you have to pull the plugs quick, right when the motor is heated (overheated). If you see the center electrode rounded off at the edges or the the edges of the outer electrode (usually right at the tip) rounded off, it can indicate you are running too lean. That white color is also an indicator, especially if the center electrode is white.

No way to retard the timing, the only recourse is to make sure your O2 sensors are good and maybe running a number colder plug.

If it gets bad enough it can actually burn a crater in the the top of the piston.

I've seen this at high speeds when the XJ is pushing a lot of air, basically the same situation as fighting gravity and pushing big tires.
 
Devilfrog said:
Are you 100% positive you've fully bled the cooling system?

Just saying as they (open cooling) aren't exactly burp friendly layouts.
With the upper hose full of air the motor will run cool just tooling around but run hot under load and at stop lights (not ovetheat hot just hotter than norm).
Click to expand...

I've had tiny seeps of coolant that were hardly noticeable. When the motor goes through a cool down cycle and sucks the coolant from the recovery bottle back into the radiator, it can also suck some air back into the system from a pinhole leak. Air is a lot thinner than water, a tiny leak with a small seep of coolant, can suck a lot of air.

I mark the high and low levels in my coolant recovery bottle (felt tip pen) and keep an eye on it.
 
Last edited:
Check and see if your exhaust is leaking and blowing hot gasses on the side of the motor? ParadiseXJ came up with a good idea, dump a little oil down the TB and see if the engine bay fills up with smoke. Worked for me.

I'm officially out of ideas. :)
 
I had checked everything before and determined it was running leaning, that is the reason I put new sensors. I will try the plugs next how do you determine ranges on them. You mentioned colder plugs.
 
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