Vey puzzling overheating issue, not the usual suspects!

[Ecomike]

water pump is wrong direction

No, nice try, but try again. Hint, it is Renix radiator, still a closed system.

 

[WEJOXJ]

EcoMike, thought you we're playing with eveyone when you made this post. You, 5-90, etc. helped me with an '00 w/ the same problem. I KNOW the Renix is a different animal and you have much more experience on these Jeeps but hear me out.

Really think you were on to something cleaning off the o2 sensor from page 1!!! Unless I missed something you ran much cooler there than with any other effort, right? Isn't it possible that unplugging the O2 sensor would perhaps just leave the reading stuck with the ECM and a cleaning masking the problem? Myself and a coworker had the exact problem on our '00's with some cutout and after doing about everything outside of replacing the radiator and having his mechanic bench test those O2's he took it back in on the rack and found 2 of the 4 O2 sensors were out of whack. Replaced and ran perfect again. Just an idea, hope it helps. Oh, there were no codes either in our situation.

 

[Ecomike]

EcoMike, thought you we're playing with eveyone when you made this post. You, 5-90, etc. helped me with an '00 w/ the same problem. I KNOW the Renix is a different animal and you have much more experience on these Jeeps but hear me out.

Really think you were on to something cleaning off the o2 sensor from page 1!!! Unless I missed something you ran much cooler there than with any other effort, right? Isn't it possible that unplugging the O2 sensor would perhaps just leave the reading stuck with the ECM and a cleaning masking the problem? Myself and a coworker had the exact problem on our '00's with some cutout and after doing about everything outside of replacing the radiator and having his mechanic bench test those O2's he took it back in on the rack and found 2 of the 4 O2 sensors were out of whack. Replaced and ran perfect again. Just an idea, hope it helps. Oh, there were no codes either in our situation.

Well that just confirms my suspicions that O2 sensors can drift and cause an overheating lean condition, with out throwing codes even in OBD-II jeeps (or other vehicles).

While my O2 sensor system maybe contributing to the problem, MY tests were not conclusive enough to get me to move in that direction yet. For now, it seems that have more than enough cooling capacity to keep up with the engine, but I will be watching things closely.

Oh, and in the case of unplugging the O2 sensor, that always forces the engine into open loop, rich mode, so no if the O2 sensor was the primary problem, it would have run cooler when I ran the tests with the O2 sensor disconnected, which it did not.

 

[Ecomike]

BTW, my last posted question.

I mentioned it several years ago in an old thread. Anyway, the reason it is progressively colder at the top right (drivers) side is that the radiator has air trapped in the top side, which in my opinion is the biggest problem with the Renix OEM plumbing after replacing parts. The air is less dense, and can not easily get to the lower outlet radiator hose. Note that the filler neck on the open system jeeps is on the right (drivers) side, so they don't have this trapped air problem! Which may be the main reason they have less problems!!!!!!

The water pump inlet hose the radiator outlet is connected to is at the bottom of the radiator. Water (coolant) is heavy than air so the air gets trapped in the top of the radiator, possibly for days or weeks, months, years (?) unless you get rid of it some other way. I have yet to bleed my inline filler neck on the inlet hose to the radiator that I have added to my set up.(2 days ago)

In spite of the trapped air (I got some out by racing the engine periodically and topping off the renix bottle for 2 hours, but it is still about 1/3 air at the top of the new radiator) in the top half of the radiator, and resulting loss of cooling efficiency, my new set up is running noticeably cooler. The 3 row brass / copper CSF radiator and the 97 year, parallel flow style AC condenser on the AC I upgraded to have both helped. I will post up final test data later once I get all the air out of the radiator. For now it ran at 185 F at the thermo housing during my final readings with ambient at 88 F, no AC. AC was still charging during earlier AC test, but it ran about 200 F at the thermo housing at idle with air in the radiator (1/3) and only 14 oz of R-134a added from a vacuumed out system! And I was already getting 50 F air out the AC vents, and 40 / 225 PSI on the gauges, on Max AC (Jeep doors shut), with 88 F ambient.

UPDATE: Last night I got most of the radiator free of air by repeated use of the filler neck I custom installed in the upper supply hose of the radiator. I highly recommend this MOD, as a way to get trapped air out of the Renix radiator. Far less messy than pulling the radiator hose off the water pump inlet and man handling the hose to try and get out, if you use the longer, multi bend hose (I recently saw a short path, less standard hose in a thread here that might be easier to get air out of).

By getting the 50% trapped air out of the radiator, my coolant temps dropped by about 40 F.

 

[Ecomike]

EcoMike, thought you we're playing with eveyone when you made this post. You, 5-90, etc. helped me with an '00 w/ the same problem. I KNOW the Renix is a different animal and you have much more experience on these Jeeps but hear me out.

Really think you were on to something cleaning off the o2 sensor from page 1!!! Unless I missed something you ran much cooler there than with any other effort, right? Isn't it possible that unplugging the O2 sensor would perhaps just leave the reading stuck with the ECM and a cleaning masking the problem? Myself and a coworker had the exact problem on our '00's with some cutout and after doing about everything outside of replacing the radiator and having his mechanic bench test those O2's he took it back in on the rack and found 2 of the 4 O2 sensors were out of whack. Replaced and ran perfect again. Just an idea, hope it helps. Oh, there were no codes either in our situation.

Last weekend we found a 2000 XJ with a low voltage to the O2 sensor heaters that was causing the engine to run rich at start up, and idle and low cruising rpms, like in traffic. It had no codes either! Wiring problem between the O2 sensors and the 12-14 volt relay.

 

[Ecomike]

Well I got 2 days of 60 mile round trips on the beast this week. It is running between 200 and 207 F at the thermostat housing, with AC on Max. in a 95 F ambient day (190 F with AC off, with a 180 F thermostat).

The filler neck MOD is working great, and is not releasing any coolant, proving my prior claims that the Renix system with air in the POS reservoir bottle is compressible, and is thus lowering the cooling system pressure, extending the life of hoses, and radiators. I now have the best (and worst) of both worlds.
Lastly, I got some real odd data on the final coolant temperatures with the new set up which includes the 3 row CSF copper/brass radiator. My old 2 row aluminum radiator had a 30-40 F delta T across the inlet to outlet. My new CSF radiator only has a 15 F degree temperature drop across the radiator. Only way the engine could be running cooler with hotter water going into the engine is if it is flowing faster!

I am still convinced my 4.0 is running is leaner, and hotter, but for now it is no longer overheating!party1:

 

[Ecomike]

Been about 6 weeks now (87 Renix update). Yesterday we got back up to about 95 F ambient, >90% humidity, and I got stuck in mid day traffic for an extra hour of crawling traffic on 33 mile trip. AC on Max, no problems. Renix bottle with Volvo cap is holding up nicely. Coolant temps unchanged, and the 16 lb cap on the inline filler neck has never opened or vented as I theorized, renix coolant bottle is still 1/2 full, unchanged, so my closed/open Renix mutant hybrid cooling system is working perfectly. Holding 180-200 F at the thermostat housing for 60 F to 95 F ambient days. Note my thermostat is 180 F.

Summary of relevant changes I made. Installed a new CSF 3 row Brass/copper radiator, new 97 parallel flow AC condensor on the R-12 converted to R-134a AC, new ZJ (grand cherokee standard FC) fan clutch, new standard water pump, and new POS plastic Renix Coolant bottle with a Stant brand Volvo bottle cap on the Renix bottle.

I have also determined that my renix is indeed running leaner, and thus hotter, which is why I had to clean up and make improvements to the cooling system. In spite of the 1 hour traffic jam and poor mileage I still got a 15% higher mileage on the last tank of gas than I got anytime in the last 4 years. I have had a bout 20% increase in mileage since my renix started running hotter.

Also note worthy is that just before it started running hotter I replaced the harmonic balancer. The jeep sat up for 4 weeks during that time. When I started it back up it had a terrible, very load valve train noise, much worse than valve-tappet-lifter noise I had gotten use to the last 40,000 miles and 4 years. So I did a trick that 5-90 taught me that had worked to some extent the last 9 months, which was to run the RPM in park up to 3500 and hold it for a minute to free up the stuck lifters. Well ever since I did that the last time, just after replacing the HB, the 4 year old lifter noise (always worse in cold weather, and first days start up) has been gone completely, and the engine runs hotter, and leaner, and gets better mileage ever since that day.

 

[Ecomike]

We have gotten down to near 20 F lately here in Houston. At about 35 F my dash reads 100 F on the coolant temp now (I think it is closer 160 F at the thermostat area, dash reads rear of the block, incoming coolant from radiator before it traverses the head), and while the cabin heat works (it is slow to warm up, but does warm up with about a 40-50 F rise at max settings, so it raises 30 F air back up to about 70 F), the entire cooling system is doing a bit of over cooling at this stage in this weather, even after a 1 hr highway drive with E-Fan completely disconnected.

What a difference a 75 F change in cooling air, with no AC makes on engine temps.:shiver:

Still have no leaks, and or further problems with the cooling system mods I made this summer. If it was any colder here, I would be blocking off the flow to part of the radiator to stay warm in the winter.

 

[winterbeater]

So you are not worried about running in rich mode? Is there a way you can tell? You must have some way to know, because I am pretty sure that you would be monitoring that.

 

[Ecomike]

So you are not worried about running in rich mode? Is there a way you can tell? You must have some way to know, because I am pretty sure that you would be monitoring that.

I have done extensive live testing on the Renix, and with the coolant at say 80 F, cold start up, the 12 volt internal electric heater (orange, third wire) in the O2 sensor gets the O2 sensor up to operating temperature in less that 30 seconds, whereas an O2 sensor with out a working internal heater will only work properly when the engine is warmed up, and under load, as the O2 sensor will only be hot enough to give an O2 reading to the Computer when the O2 sensor is hot enough, and a hot idle by itself is too cold! That is why they have the electric heater built into the O2 sensor.

If the Renix computer has a reasonable temp reading from the CTS, and a working O2 sensor circuit, it will go closed loop very fast after a cold start, even when the engine is still cold as hell.

At that point the Renix computer, if it has what it considers to be good reliable data from several of the engine sensors, will switch to closed loop operation.

I am not saying you don't need a good CTS. You do. But a CTS that is off 100F, and reads 50 F all the time, or reads 50 F when it is 150 F, will not, by itself stop the Renix computer from going closed loop (it will stop the OBD-II from going closed loop, or so I am told). The bad CTS data, however, will waste fuel at various points like WOT, as the computer is using the bad data, and trying to run it too rich. Once the Computer is running closed loop, say at cruise, it should ignor the bad CTS data and over ride it in closed loop A/F calcs based on the O2 sensor data, which is what the computer uses for fuel trim control.

Letting mine run at say 160 F, instead of 200 F, looks to be costing me about 1-2 mpgs at 60 mph cruise, because the air is colder and denser in the intake manifold and uses more fuel. Around here it is a lot of stop and go driving, so not sure it makes a real difference.

 

[Ecomike]

I discovered recently, while doing an AW4 swap, that the donut flange exhaust at the manifold to exh-pipe, was loose, nuts were loose enough that it had to be blowing hot exhaust on the block, which was another part of my 2009 summer over heating problems.