Yet another Renix overheating thread

This issue has been extensively documented here by people like EcoMike but I thought I would do my own thread as I diagnose and repair mine. I have a 1990 Cherokee that had a 300K wonder of an engine. Always ran in the 190-200 degree range, occasionally spiking up to 210 going uphill on the freeway without the stock engine skid on. (More on that later). I have a winch and lights blocking airflow through the radiator. Rings were shot and it had blow by that required special plumbing to avoid it becoming some kind of Nazi extermination device. Compression was around 90-100 on each pot with one down around 75. Oil pressure was embarrassing but did not seem to bother the engine. The mill we all know and love. Never even thought about the cooling system. Had a 6 year old water pump and a plastic 1, or 2 row radiator from the middle ages. I hard wired the electric fan circuit for occasional use on the trail. It never overheated except the one time it blew a heater hose. Anyway I got tired of putting oil in it and gassing my passengers but it worked like a champ.

Fast forward:
Acquired a chrysler rebuilt Renix engine for $250 with 150K approx, since rebuild from a reliable source who told me that it had "ran fine" when pulled a year ago. It had sat in his shop for that time. He had it for sale before it was pulled and I had asked him for compression and oil pressure reports at the time. 135 psi each cylinder and great oil pressure. We could not agree on price. When he finally dropped the price to a fraction of what I had originally offered I figure "what is the worst thing that could happen" So I swapped over the engines after doing the requisite RMS install while the engine was out.

I did commit the cardinal sin of not flushing the engine cooling system out before running it which I regret. Will admit that now. I was more worried about whether or not the thing would actually run, that the valve seats would be rusted and pitted Run it did. It started on the very first crank great compression and oil pressure. (Love these engines).

So I have now been running the beast for a couple of months and the only issue I have with it is that it runs at about 210 at idle and regularly gets up to 225-230 under load. My engine skid no longer has any impact. My own theory here is that the engine skid works like a spoiler and will actually suck air through the rad. Manifolds, sensors, injectors are all off the old mill including temp sens. Now this is not necessarily bad but like EcoMike I want the cooling system to be the best it can and my wife complains that the engine "smells hot" ( I hate this) when going uphill on the freeway. I do think it is a little close to the ragged edge. Summers here are not horribly hot but I actually would like to take this rig to Moab at some point. BTW I am not interested in going to an open cooling system and am not going to debate that bit.

So working theories in order of likelihood imo:

1:I have clogged the rad up with stuff from an engine sitting for a year.
2: That an engine that actually has compression runs a little hotter and that the old cooling system is not up to the added requirements.
3: The POS Hayden fan clutch that I installed is not working.
4: Head gasket
5: Water pump/thermostat
6: Radiator tired
7:After reading EcoMike's saga air trapped in top of rad

My plan is to document my steps and report on the results.


Step 1: Thanks GoatMan, Perform exhaust gas detection test on cooling system: Passed

Step 2: flush the system: In process and will report.

Step 3: Inline filler neck: In process and will report

My plan is to go through the system and replace parts that are unknown to me. I will be installing a CFS 3 row radiator and a Hesco water pump,a robertshaw 180 deg stat and a ZJ HD clutch.

More to come

Quick update. After a slight misunderstanding with DPG offroad I ended up with a open CSF rad. Will be doing an open cooling conversion at this stage as it is just easier than shipping it back and getting another shipped out. Oh well. One small detail the old engine had an 180* stat. New one has 195*. Am a little cheesed here. I actually really like the MAC expansion tank setup. Maybe I will just keep the thing closed.

Keep it closed, you will not regret it!!!

Hey thanks Sir. I actually realized that using an open radiator in a closed system means that I should not have to use the Moroso inline filler neck now. So if anyone wants one cheap. Have ordered the 82 corvette fan switch that I will stuff in the 94 thermostat housing I have so I am almost OK with not getting the right radiator. Plan right now is to keep it closed as I think that is the best config for this rig.

One of the really COOL (LOL) things about the closed system, is that it runs at a lower pressure, and averages about 8-10 PSI, while the closed system is at 16 psi all the time! Easier on the hoses, etc!

Nice to know somebody read my posts!

If you search around here, you should find some advice I've given (sorted out myself, mostly) on the RENIX system that works rather well!

I'm a bit leery of the "open" cooling system - out of the five RENIX rigs I've owned to date, the one that ran hottest was an "open" conversion (that was done before I bought it. I was seriously considering a retrofit to the OEM "closed" system.)

People are down on the closed system - but if it's so bad, why has it been around so long and why are OEMs moving more toward it? I had a 1991 Corsica V6-3.1 - closed system. I've worked on plenty of other Chevvies with the closed system. The Volvo closed system tank (I don't recall the specific application) is a common upgrade from the RENIX volume tank. My wife's 2005 Suzuki has a closed system.

Common thread? The only time any of these vehicles has overheated was either 1) due to component failure, 2) due to aggressive lack of maintenance.

The OEM RENIX radiator tends to start having trouble at 150-180Kmiles - replace it with a good aftermarket unit and you'll be fine (I usually use Modine.) Do replace it with an all-metal radiator (I prefer copper, but aluminum is okeh,) and forget about the idea of an aluminum core with crimped-on plastic tanks - which is a stupid idea.

It's easy to keep the closed system in good operating trim - and I've told how to do it often enough that you should find it easily (and I honestly don't feel like typing it all out again...)

Totally agree on the closed system... I got a little discouraged when I got the radiator with a cap before I realized I can keep the system closed and just run 2 radiator caps.
Thanks for the posts.

New plan:

Hesco water pump installed
Mr. Gasket 180* stat
CSF 2741 3 row radiator (open)
94 thermostat housing
82 Corvette Fan switch in thermostat housing with toggle switch for manual operation
Continued use of the MAC aluminum expansion tank
ZJ HD fan clutch
VDO 270* electric temp guage

Will report on results when I get everything back together.

180 t-stat is not a great idea, but may work.
Hoestly, my Renix runs great. Haven't checked the "true" temp with a gauge/heat gun. But overall, runs at around 205. In 2010, heading to big bear, ca via hwy 18 on the grade It was running pretty warm. Got 2/3rd's the way between 210 and the 3rd mark. I pulled over in a turnoff and just let it run at idle for a few minutes.
After that it no issues.
With your overhaul, you shouldn't have problems.
A mech. fan delete/full e-fan setup may help also. If you have the funds I would do that.

Johnnie Walker said:

180 t-stat is not a great idea, but may work.
Hoestly, my Renix runs great. Haven't checked the "true" temp with a gauge/heat gun. But overall, runs at around 205. In 2010, heading to big bear, ca via hwy 18 on the grade It was running pretty warm. Got 2/3rd's the way between 210 and the 3rd mark. I pulled over in a turnoff and just let it run at idle for a few minutes.
After that it no issues.
With your overhaul, you shouldn't have problems.
A mech. fan delete/full e-fan setup may help also. If you have the funds I would do that.

Click to expand...

Apart from my 88 (that didn't like a thermostat at all,) I ran a 180* unit in all of my RENIX rigs - opening the coolant flow sooner helped to keep temperatures down. The two biggest temperature-reducing factors were probably the 180* thermostat and the addition of Water Wetter to the system.

OBD would be a bigger issue with depressed operating temperatures - but I've been able to pull the operating temperature of my RENIX rigs down to 190-195* without any negative effect on the engine, emissions, lubrication, or anythign else. I didn't like running up around 205-210*, so I did something about it. Worked rather well.

You can find out how I did it with some searching - I've posted how I've done it here before.

I just wired in 2 big honkin fans with my open system conversion on my renix and I run around 200 all the time. If the engine is running the fans are on all the time, I pulled all the parts including the radiator out of a u pull for about $50. I don't think I personally would run the 180 thermostat but hey maybe one day ill get a wild hair and throw one in and see what it does but for not I am content with my setup.

So as I mentioned my previous engine ran a 180* thermostat and always ran perfect temp wise. I was curious to see why, with the same cooling system, the replacement engine would run quite a bit hotter. One theory was it actually had more compression = more heat to dissipate. Now I suspect that the difference was essentially that the new engine came with a 195* thermostat. Correct me if I am wrong but with the hotter stat you have essentially moved the goalposts up 15 yards so the engine will never run cooler than 195* because if it does the thermostat will close and bring up the temp. I could argue, and will, that on a RENIX engine, with the cooler stat the engine will engage cooling early which can better control any load induced spikes on the system. I won't even get into the issues around the fact that at it's stated temp a thermostat only begins to open.

This is what I saw on the old engine. When I was going uphill on the freeway I would spike up from 190* or so to 210* with the new one from 210* to 225*.

While it is often cited that 210*is the "normal operating temperature" the FSM studiously avoids saying what it is. There are links out on the web to the maintenance bulletins that indicate 192* - 198*. What the FSM does say is that the fan is supposed to come on at 190* and it says that the thermostat should be 195*. which does not really make sense. Here is my opinion. Running on the cooler side and given that the computer does not care on a Renix mill, may cause the engine to be a little less efficient but running on the hotter side increases the likelihood that the engine will spike up to unhealthy temps under extreme load. (I do extreme load). Therefore I will start with the 180* stat and if it cools too much I will graduate to the 195*

My only concern would be that the coolant may constantly circulate if your air movement isnt enough to drop the temp of your coolant and close your thermostat. If it's 95 degrees on a trail and your idling i could see overheating issues happening. But again I am not experienced in this area so this is just me throwing my thoughts out there if anyone can explain it to me better please do.

nickguy said:

What the FSM does say is that the fan is supposed to come on at 190* and it says that the thermostat should be 195*. which does not really make sense.

Click to expand...

Actually on the Renix it makes perfect sense. The temperature from point to point in the renix can vary by 15 F in a very well cooled (upgraded system), and in a poorly maintained system can vary by as much as 60 F or more, between the thermostat and the E-Fan T-Stat switch. The HO is different, in that the ECU controls the E-fan, and the Temperature sensor the HO uses in the T-stat housing, not at the radiator outlet!!!!!!!!!

The Renix temperature switch for the Renix E-fan is on the cold side of the radiator. I have seen temperature drops across renix radiators from 15 to 60 F. The 15 F drop was a clean 3 row copper radiator, and the 60 F drop was a poor flow, nearly completely clogged radiator. The clogged system had a 235 F inlet peak and 175 F outlet temp peak on the radiator (which was baffling), and the new radiator was 195 F inlet and 180 F outlet temp. The difference which I could not measure, was the flow rate between the partially clogged radiator and the new, high flow (3 row) rate radiator.

The clogged radiator never tripped the Renix E-fan, while the engine overheated!!!!!!!!!!, but the new radiator did trip the E-fan, because the hotter water reached the E-fan temperature switch, due to the higher flow rate (new radiator was not partially clogged inside).


If you have a constant, steady heat load on the engine, and if it is high enough, it will not matter if you have a 180 or a 195 F thermostat, if it is running at 200 F, steady state.

If however, the load varies in a cycle, and the E-Fan cycles, a 180 T-stat can buy you more time before the temperature peaks again, when you hit a high load, like climbing a grade. If you are going up and then down, in a cycling fashion (hills), then a 180 F T-stat can limit the peak temperature to a lower number than a 195 F T-stat, as it can cyclicly recool to a lower temperature before the next grade climbing point.

Lastly, the Renix radiator easily traps air in the top 1/3rd of the radiator, reducing the cooling capacity of the Renix radiator by 35%, and that trapped air defies ever being removed due to the very poor design, plumbing layout, which is why I went to an inline filler cap on the radiator inlet hose.

I have a 16 lb cap on my inline filler cap, no overflow bottle, and the Renix plastic turtle bottle (1/2 filled with air), with a Volvo cap on the bottle which is also a 16 lb cap, and the inline filler neck has never in 2 years of running now, never opened once!!!!!! My system runs at about 8-9 psi, at about 200 F peak temperature (105 F day, 90% humidity, with AC on Max, at idle for 30 minutes, in gear, with parking break on) now, with a 180 F T-stat. I have used 180 F T-stats in Houston for 35 years. And I have had rigs that nearly made 500,000 miles.

Got all the mods done. Am still waiting on an accurate temperature gauge and I am too cheap for a IR gun. Ran the rig up I90 to the mountains yesterday after getting everything installed. No fan switch/sensor yet but that is on the way from Rock Auto ($10).

So on the factory temp gauge the rig stubbornly sits right under the 210 mark. From my interpretation of the marks I would say that it is right at around 195*. It does not matter what I am doing, idling, city driving or running at 3500 revs in 4th on the freeway. I am very pleased and will follow up with more detailed of a report when I get the new gauge installed and some wheeling. It does feel like I have more power.

Albeit I did it by accident it might be a good idea for those brave few of us running RENIX rigs and who understand the advantages of the closed system to consider the idea of buying an open CSF radiator for your refresh but keeping the system closed. The second radiator cap makes filling very easy and addresses the trapped air issues so well documented by EcoMike, without resorting to the inline filler neck. The ZJ fan clutch is working as advertised and so far I kind of like the noise but I could see getting sick of it on a daily driver. For my rig it is perfect and makes me worry less about my winch and Cibies blocking air flow.

So to recap...

CSF open Radiator #2671 Dirk at DPG offroad www.dpgoffroad.com has reasonable prices and will make sure you get the right radiator. If you want the old closed style be sure to tell him.

Hesco water pump

Mr Gasket 190* Thermostat

94 Thermostat housing Junkyard

82 Corvette fan switch (Rock Auto)

ZJ HD fan clutch NAPA #272310

MAC aluminum expansion tank

18 pound cap on the Radiator 16 pound on the MAC expansion tank.

I did use a lower hose with a spring in it but it chafed and blew so I am running a replacement hose without the spring and a piece of the old hose protecting it from chafing on the PS pipes. Kind of think the Renix does not need the spring.

Think that the upgrade will significantly improve the life of this engine.

Good tech here. Glad it's all working out. I learned a thing or 2...

Harbur Freight has decent IR temperature sensors for under $20 on sale frequently. The $4.95 one is not that accurate, but I got the good one on sale $9.95 IIRC. It was how I found the hot and cold spots in the radiator that confirmed trapped air in the top side, and got me the temperature drops across the radiator.

If you can not swing $9.95 to $14.95 for one, then you are right you are,..... CHEAP!

LOL


:cheers:

just went to a open system on mine and it runs about 5 to 10 degs hotter then the closed system did about 200 most of the time with ac on in 100 deg weather 210

"If you can not swing $9.95 to $14.95 for one, then you are right you are,..... CHEAP!"

Might be able to swing that . I was looking at one at Frys that they had for $80. I could read the temp on the casing of an AC unit hung from the ceiling 200' away. Just not sure I have the need for that.

This is the real good one they have:

http://www.harborfreight.com/infrared-thermometer-93984.html

They have a cheaper one, but it is too sensitive to distance from the sample spot.

So an update....

I did a wheeling trip that involved a couple of mountain passes.

The problems I had were the rig never did get that warm. Actually coming down Chinook pass the thermostat housing temp was less than 150 degrees. My concern was that cooling was so efficient that temperatures rarely got much above the thermostat opening temp and that the thermostat seemed rarely to open fully.

Think this is a NW issue. Our ambient temps are so much lower. I did get the HF thermostat to confirm temps.

So I swapped the stock fan clutch and the 195* thermostat back in. Now the temp is more stable in the 190* - 200* Will post more when I get some detail about performance under load.