Renix 4.0 overheats when driving

[jamespwsullivan]

My brother and I have been chasing a hot running problem on my MJ 4.0 I6. The block and head are from a 2003 TJ, the intake is ‘87 Renix, and the cooling system is closed.  I just read pizzaman09's post and don't see anything that fits that we haven't addressed already.

 

Here’s the question: Is the next right step is to pull the head off?

 

If/when we pull the head, we’re going to look for blocked cooling passages and/or a failed head gasket that is allowing early coolant return (h/t to Ryan Aumiller in the Jeep Renix group on FB in response to my post from August 2021):

 

https://www.facebook.com/groups/391733537829621/permalink/1505664613103169/

 

There is no visible sign of coolant and oil mixing in the crankcase.

 

A couple of things that could be tried before pulling the head:

(1) pull spark plugs and look inside cylinders with a boroscope to see if one or more cylinders is/are “too clean”, suggesting coolant intrusion

(2) test for combustion leaks (using this detector from HF):

 

https://www.harborfreight.com/combustion-leak-detector-64814.html

 

The current sitch is that the things we have done (listed below) have helped but we are still seeing temps of 225 F - 230 F on the Renix Engine Monitor (REM) under load. We have heard from many REM owners members of this group that temps at or below 210 F on the REM are to be expected. (We don’t currently have a factory temp gauge so the REM is our only coolant temp source at the moment.) 

 

https://nickintimedesign.com/product/renix-engine-monitor-ii/

 

Also: This is a road vehicle—we’re not talking about trail use but it does have 35” tires on a 5” lift with an AW-4 transmission, 4:10 gearing.

 

Unless there’s something else obvious that we’re missing, you’ll probably agree that this is a head-scratcher.  Other than the two things mentioned at the top is there anything missing from what we’ve addressed that might impact the efficiency of the cooling?

 

Already done:

(1) all applicable Cruiser54 tips

(2) IR thermometer check (no particular hot or cold spots found)

(3) tested and replaced all sensors that were out of spec or believed to be janky

(4) new water pump

(5) new 195 F thermostat

(6) new coolant pressure bottle and cap

(7) new full-width aluminum radiator (Spectra CU78)

(8) replaced single crank-driven radiator fan with two factory-style aux electric fans—1 controlled by sensor mounted in radiator fins (203 F on) and other by REM (210 F on)

(9) Bleepin’ Jeep style 3-part cooling system flush (done 9x [yes, really] – until coolant retained green color)

(10) bypassed heater core (temporarily) to eliminate it as a possible problem source.

[87MJTIM]

Lower radiator hose old or bad?  With the engine running it may collapse restricting coolant flow 

[Ωhm]

REM ?'s

Closed Loop? INJ PW? °FIA? STFT? LTFT? Wondering if your engine is running LEAN.

[jamespwsullivan]

Thanks for the early feedback.  Lower radiator hose seems fine.  Not ancient but not brand new either.  I'll report back on the REM/ECU info the middle of next week when I can physically get back to the truck.

[m2bandit]

15 hours ago, jamespwsullivan said:

 

Already done:

 

(8) replaced single crank-driven radiator fan with two factory-style aux electric fans—1 controlled by sensor mounted in radiator fins (203 F on) and other by REM (210 F on)

I'd get a clutch fan that works. I have a fan clutch eliminator on my XJ it works great, but it's a crawler

Either way the tiny Renix alternator suffers enough as is.  I've been through every cooling mod when I was younger. Electric fans were the biggest waste. If the stock fan can cool my stroker pushing 41's it can handle street use.

 

I don't see mention of burping here.

I like to first fill from the top rad hose. Then remove the temp sensor on the back of the head, park the jeep nose down and fill it while at operating temp until it comes out of the sensor hole. Reinstall sensor, place cap on. Take a couple short drives getting up to operating temp (210 I think) and check fluid each time. If you don't have to top off you're good.

 

 

[jamespwsullivan]

@m2bandit 

I don't see mention of burping here.

I like to first fill from the top rad hose. Then remove the temp sensor on the back of the head, park the jeep nose down and fill it while at operating temp until it comes out of the sensor hole. Reinstall sensor, place cap on. Take a couple short drives getting up to operating temp (210 I think) and check fluid each time. If you don't have to top off you're good.

 

The head is from the 2003 TJ so does not have a sensor at the firewall end.  We did burp the coolant the best we could without the access and did this--->  You can see one of many discussions here:

https://www.naxja.org/forum/showthread.php?t=939188

about a procedure we used that involves tiny holes in the thermostat.  What I can say is that the coolant level is stable over 200 miles of driving.

 

Your comment about putting a mechanical fan back in use is interesting.  The spec'ed air flow from the electric fans seems adequate but I'm about out of ideas so I'll see if I can source a fan and clutch from the JY.

 

Thanks for the ideas.

Edited April 17, 2023 by jamespwsullivan
adding content

[jamespwsullivan]

@ Ωhm - Double checked before I responded... No it's not running lean and yes it is running in closed loop as would be expected.

[Ωhm]

Closed Loop is a good thing.    

[jamespwsullivan]

On 4/16/2023 at 7:28 AM, Ωhm said:

REM ?'s

Closed Loop? INJ PW? °FIA? STFT? LTFT? Wondering if your engine is running LEAN.

Here's what I found from the last time I dumped a log from the REM.

STFT range between 133 and 158
LTFT steady at 128
CLOSED LOOP - seeing it switch to closed shortly after starting
INJ Pulse Width (PW) - range between 6.9 and 7.4
Intake Air Temperature (FIA) - The header in the data log file form the REM shows this as "IAT" rather than "FIA" but that's not the interesting find.  It is stuck at 68 degrees which surely means something about the sensor.  It sure is not hotter than the outside ambient temperature although I will test again since the daytime temps have dropped since the last time the truck was run.
LEAN versus RICH - Sure it swaps back and forth but is not stuck in a LEAN state for any big amount of time.

 

[Ωhm]

STFT is saying throw more fuel at it, yet LTFT is steady at 128. INJ PW seems high (normal 5.5mS-5.8mS), but this ain’t factory stuff and your at CLOSED LOOP, which means your well within the Range of Authority for the ECU.

 

IAT needs some looking into, sensor is hard to get now. Not sure if this would cause high ECT numbers.
 

[jamespwsullivan]

On 4/18/2023 at 12:06 PM, Ωhm said:

STFT is saying throw more fuel at it, yet LTFT is steady at 128. INJ PW seems high (normal 5.5mS-5.8mS), but this ain’t factory stuff and your at CLOSED LOOP, which means your well within the Range of Authority for the ECU.

 

IAT needs some looking into, sensor is hard to get now. Not sure if this would cause high ECT numbers.
 

Going to try a different efan next.  I'm looking around to see if I have a spare / known-good IAT sensor.  Thanks

[m2bandit]

On 4/17/2023 at 4:55 AM, jamespwsullivan said:

The head is from the 2003 TJ so does not have a sensor at the firewall end.  We did burp the coolant the best we could without the access and did this--->  You can see one of many discussions here:

https://www.naxja.org/forum/showthread.php?t=939188

about a procedure we used that involves tiny holes in the thermostat.  What I can say is that the coolant level is stable over 200 miles of driving.

 

Your comment about putting a mechanical fan back in use is interesting.  The spec'ed air flow from the electric fans seems adequate but I'm about out of ideas so I'll see if I can source a fan and clutch from the JY.

 

Thanks for the ideas.

Not sure that will help but it definitely can. Renix jeeps came with as low as 60 amp alternators.

 

Quote

This is the alternator output on my 91 XJ @ idle under the following conditions:
engine running, battery floating fully charged (all other electrical accessories off)--16 amps
+headlight switch fully on--30 amps total
+blower motor "hi"--43 amps total
+radiator cooling fan running with AC on--56 amps total
+fog lights (aftermarket)--65 amps total
 

It's also worth noting the aux fans need 30-40 amps each to start. Low voltage would probably decrease life of other electrical components/alternator.

 

You can also put on a 91+ thermostat housing and add a petcock to it. I don't know how people use that for burping but I bet a NAXJA search would pull it up.

I also use the Prestone flush kit on my heater hose. This will add another accessible high point. Some people don't like the idea since it adds a point of failure but mine has never exploded ;)

[rokinn]

4 hours ago, m2bandit said:

You can also put on a 91+ thermostat housing and add a petcock to it. I don't know how people use that for burping but I bet a NAXJA search would pull it up.

I also use the Prestone flush kit on my heater hose. This will add another accessible high point. Some people don't like the idea since it adds a point of failure but mine has never exploded ;)

I put a 91+ thermostat housing on mine.  Before I installed the electric fan I just had a plug in the hole.  Have a thermostat with a hole in it and the 91 housing with the plug removed when filling.  When coolant starts coming out the housing hole put it back in and you're pretty much have the system bled.  I now have a switch in that to turn on the efan I installed.  I never overheat now whereas I had a lot of problems overheating before, especially when idling for long periods, going too slow or towing up a steep hill.  If I need to fill the system now I just remove the switch.

 

It's a great addition. 

[jamespwsullivan]

On 4/20/2023 at 2:27 PM, rokinn said:

I put a 91+ thermostat housing on mine.  Before I installed the electric fan I just had a plug in the hole.  Have a thermostat with a hole in it and the 91 housing with the plug removed when filling.  When coolant starts coming out the housing hole put it back in and you're pretty much have the system bled.  I now have a switch in that to turn on the efan I installed.  I never overheat now whereas I had a lot of problems overheating before, especially when idling for long periods, going too slow or towing up a steep hill.  If I need to fill the system now I just remove the switch.

 

It's a great addition. 

Good suggestion and I have heard similar before but without the detail.  As long as the thermostat housing is the high point the burping should work as needed.  I alrday have a thermostat housing with a sensor in it and will try that procedure.  Thanks

[jamespwsullivan]

On 4/20/2023 at 10:02 AM, m2bandit said:

Not sure that will help but it definitely can. Renix jeeps came with as low as 60 amp alternators.

 

It's also worth noting the aux fans need 30-40 amps each to start. Low voltage would probably decrease life of other electrical components/alternator.

 

You can also put on a 91+ thermostat housing and add a petcock to it. I don't know how people use that for burping but I bet a NAXJA search would pull it up.

I also use the Prestone flush kit on my heater hose. This will add another accessible high point. Some people don't like the idea since it adds a point of failure but mine has never exploded ;)

So we're going to replace the fans with a setup that has a higher air movement output (cfm.)  That's going to happen whether it is the real issue or not because I am now convinced that the two aux fans do not out put the same amount of air as a mechanical fan plus one aux fan.

 

I can't find a part number on the Delco-Remy (stamped) alternator but I have a strong suspicion that it came with the TJ block.  In any event I think I'll put a new alternator on the list.  Need a known quantity... 

 

Last but not least, someone on FB asked about reverse rotation water pumps.  The pump on this TJ block (2003) does run CCW as opposed to the crank which runs CW.  However, a guy I really respect on the wranglertjforum.com says that a reverse direction pump cannot be installed on a 1999 and older block, so it make sense that you can't go the other way either.  That doesn't mean that the water pump isn't a suspect though.  It isn't leaking but almost everything I haven't touched on the cooling system is still a suspect.  LOL

[jamespwsullivan]

A bit of an update with more to follow on another thread when I get a minute.  The fan installation was not trouble free but with some creative thoughts about spacing on the mount points the finished product is pretty good. And as expected, it did not resolve the overheating issue.  The KSuspensionfab kit optionally provides a sensor and Tee for the thermostat housing. After reinstalling the factory sensor (for the supplied fan controller) in one side of that Tee, the dash temp gauge isn't registering properly - actually is isn't registering anything.  We just installed that instrument cluster but the gauge was working before we moved the sensor.

[cruiser54]

what radiator do you have?