Renix Thermostats?

Two Questions? More might arrise as I type.

1.) Renix Temp. Settings
A. The Renix like to run at 210* F?
B. What is "Safe Mode"?
a. Can Safe Mode cause red line overheating in 80*F weather?
C. What are all the sensors used in the computer to monitor temps?

2.) Engine Internals Causing Heat Buildup
A. Can piston ring wear cause extreme temperatures?
B. What can cause extreme heat buildup other that a faulty thermostat?


Im trying to diagnosis my engine. In June my thermostat failed and I replaced it with a fail safe which failed from the engine getting to hot so it has been in there stuck open since July. Ive read that a open thermostat can cause temps to rise further than normal. The Aux Fan works since Ive added a overide. In the hot days of August the engine got up to temp but after a couple more minutes temps rised more to the point of overheating. I believe the problem is piston rings failing, messy valvetran, or time to swap in my closed alunimum 3core radiator. Ive ran cleaner through the system and it worked better for awhile after a couple flushes but still heats up. My XJ has over 227,000 miles on it so ring failure is comming soon. I have since switched to 10W40 seeing my bearings have wear on them. Valvetran I suspect because last time I had the valve cover off it was gunked up so I cleaned the best my tools could. So right now I suspect my computer is in safe which explains the drop in gas mileage and overheating in the 50*F weather of september. Now it stays super cool the second mark and our high tomorow is 32*F and Id like to have a heater and a good cooling system to keep the motor running til the stroker goes in.

So please answer the above questions and...

3.) Choices
A. Is it time to go closed cooling system or keep looking at other problems?

sound like you got a plugged rad. The added frictions might make it heat up a little more than normal. I would start with the rad first. make sure it free. It's an 88 right? you swapped to an open cooling system right.

No, he's probabably got the closed system right now, and is thinking about going to the open system.

Probably just mixed up the words, it's very easy to do.

What I did to cure my overheating problems. Replaced the radiator, I could look in the outlet hole and see excessive buildup. Replaced the fan clutch, mine would overheat mostly at or near idle. Put a bypass switch in for my aux fan. Put in an OEM thermostat and gasket. Replaced my surge tank and pressure cap (yes the surge tank cap is a pressure cap).
I also made sure the entire system was completely leak free. I had a couple of tiny seeps, that would evaporate before the coolant got very far. No drips evident in the street. But noticed I had trouble keeping the system free of air. I figure the seeps were sucking a little air in during the cool down cycle which eventually built up to enough air volume to cause trouble.
I haven't managed to overheat mine in over a year now. It has 213,000 miles on the clock.
Best guess would be you have air in the system. It goes along fine for awhile then spikes suddenly.

the closed cooling system is a bit funny about air trapped in the block.
Are you sure that you've gotten it all out?
I like to drill two holes in the new T-stat, at 12 and 6 o clock in the flange, so it can bleed air out.
I had problems with mine for months, until I went and got the super duper premium stant t-stat that costs $12.
Mine runs at 195 and doesn't flinch, it will hit 220'ish or so when on the trail in 90* heat. The last overheat problem I had was towing my brothers junk out of tellico for 3 hours, hard to blame it for that one.

The temp sensor that the ECM uses is on the side of the block, right next to the knock sensor.

I like your organisation - makes it easier to sort out the reply...

1A) The RENIX setup is designed to run at 210*, but I've pulled that down to 190-195* without ill effects, and a slight reduction in emissions (verified by CARB. Now, if they'd just let me get rid of that damned EGR...) You can use a 180* instead of a 195*, but either will work neatly - provided your cooling system is up to scratch.

1B) What you may be referring to by "Safe Mode" would be properly called "Limp Home Mode" (I think you're getting Jeep confused with Windows...:nono: ) which is the "just make it run" mode that OBD has programmed into it. I believe RENIX does as well. It's a fairly conservative batch of settings in the engine controller that allow the engine to run - not efficiently, but run. It gets you home so you can fix the thing, and is used when there is a major error in the control system - mainly, a bunch of sensors (or one semi-critical one) goes South on you. RENIX can compensate for quite a bit before going into "limp home" mode, probably because it was designed and built by Bendix/King (they also do avionics.)

1Ba) It should not, but it's possible.

1C) RENIX has a total of three temperature sensors:
A) In the cylinder head, driver's side rear (for the IP lamp/gage)
B) In the radiator tank, driver's side (for the electric cooling fan)
C) Driver's side of the engine block, behind the exhaust manifold (for the ECU.)
Of these three, you can probably consider the third to be "critical." If you suspect that the IP gage is misreading, replace the first one. (These were later gradually combined.)

2A) Not very likely. It can, but piston ring wear is more likely to cause loss of power (losing compression seal) and could also cause elevated HC emissions levels (excessive blowby.)

2B) Causes of "excessive heat buildup"
1) Failure to properly "bleed" the system - an air pocket will cause the thermostat to not open.
2) Compression leak (head gasket or head crack) into the cooling system - causes an air pocket behind the thermostat.
3) Excessive sediment/scale buildup in the radiator core. It doesn't take much to kill the efficiency of the radiator, and I've heard from several Jeep techs that the OEM RENIX radiator is only good for 150-180Kmiles on average, before it gets plugged in the core and wants replacing. Even the techs at the local use aftermarket radiators (I like Modine - been using them for years. Dirk at DPG also sells CSF radiators - they've got good reports from the field, and he's a sponsor here! Don't bother with the plastic-tanked metal cores - get an "all metal" radiator. - like the Modine or CSF.)
4) RENIX fan clutch life seems to be about five years - I replace mine every four.
5) Make sure the radiator fins aren't blocked or coated with mud - it's best to use a hose nozzle that gives a fine, high-pressure stream and flush the radiator out from the back side.
6) Regarding leaks, check all hoses and make sure the plastic "volume tank" up by the firewall has a good pressure seal. Service life of the thing seems to be about ten years. I've heard good reports from the field on using, I believe, a Volvo unit from the junkyard - but I get OEM replacements via mail-order from Morris 4x4 Center (I believe they're now at www.cyberjeep.com. They were changing domains, so it's best to Google them.) A new tank with cap went for about $25 last time I ordered a batch of them - I like to keep at least one spare on hand. There are also aftermarket metal replacements - one that fits in the OEM location can run you up to $150, but you can also use a Moroso pressurised "catch can", remove the bracket, and adapt the mounting - it's been done and covered here. Either way, you'll suddenly use a standard radiator cap - get a 13# cap.

87manche gives good advice on drilling the thermostat (I wonder where he got it?:rtm: ) because it's the same thing I've been doing for a number of years. It makes the system self-purging of air, even if it should accumulate later due to, say, a compression leak. I'll usually drill a pair of 1/16" holes in the flange 180* apart, and install them at 12:00 and 6:00, as mentioned. The upper hole passes air out of the engine, and the lower hole passes water into the engine, to displace the air.

N.B. - even if you have only small hose leaks that don't drip on the ground, you can still usually spot them by the whitish deposits that the coolant leaves as the water boils off...

Im just going to replace the thermo and radiator this weekend. When I flushed alot of grey scale came out so now Im sure its clogged. Also the hose on the tank has white dried up fluid on it.

So probally air and clogged.

16 psi is default for the open system -

The closed system uses 13 once you get the standard cap pressurized tank for the closed system?

And then 6 psi was default for the threaded closed system cap?

Blaine B. said:

16 psi is default for the open system -

The closed system uses 13 once you get the standard cap pressurized tank for the closed system?

And then 6 psi was default for the threaded closed system cap?

Click to expand...

Don't know - but I checked some RENIX caps I had at school (new and used,) and they all tested around 13psi, as I recall.

I've got to get my own pressure tester one of these days and retest now. But, I honestly don't see any reason to go up past 13psig for the cap anyhow - operating temperature is 210-215*, not up around 250*! (Isn't it "boiling point goes up 3* per pound of additional pressure above atmospheric? A 13# cap should give you about 240* before you get boiling and steam pockets, no? Correct me if I am wrong, please!)

I boiled over a few times with my open system and cap at 13# until I figured out that OEM stock caps were 16#.

Got a 16# stand cap and haven't had any problems.

Of course that's with the open system. Just tossing out my experience. Apparently 3# makes a difference. Women think so too lol.

Blaine B. said:

I boiled over a few times with my open system and cap at 13# until I figured out that OEM stock caps were 16#.

Got a 16# stand cap and haven't had any problems.

Of course that's with the open system. Just tossing out my experience. Apparently 3# makes a difference. Women think so too lol.

Click to expand...

Three pounds, or three inches?:roflmao:

I could be remembering wrong as well - but I can't find my notes at the moment. I just can't see running the 16# cap when 13# will give you plenty safe margin (speaking at literal temperature/pressure terms) and would put a bit less stress on cooling system components and seals

Of course, I've also got the RENIX that won't run normally with any thermostat installed - it overheats. Leave it out, and it will heat up normally and run just fine - it's been cross-country a few times without the thing. I still can't figure it out - it's been thoroughly flushed and the radiator has been replaced - in fact, the only part of the cooling system I haven't replaced (with stock or my own modification) is the heater core. Just haven't bothered - thing isn't leaking...

haha..now you're talkin!


However the open system is designed to run at 14-18 psi so 13 is below it's operational limits.....so perhaps thats why I boiled over for no reason two or three times.

I've heard about you not using a thermostat in one of your Jeeps.

Does it take any longer for it to get up to operating temperature? I'm sure it doesn't matter though since you live in sunny CA.

Blaine B. said:

haha..now you're talkin!


However the open system is designed to run at 14-18 psi so 13 is below it's operational limits.....so perhaps thats why I boiled over for no reason two or three times.

I've heard about you not using a thermostat in one of your Jeeps.

Does it take any longer for it to get up to operating temperature? I'm sure it doesn't matter though since you live in sunny CA.

Click to expand...

Yeah, it's one of three vehicles I've that that do not like thermostats. I've no idea why. (The other two were a 1985 Chevvy Cavalier with the 2.8L, and a 1980 Honda Accord with the 1800c/c CVCC.)

Oddly enough, it doesn't take any longer to get up to temp - not here in town, or up in the Sierras in wintertime. Heat works fine, gets up to temp quickly, and it doesn't have any complaints (unless I put in a thermostat again - every time I've tried that, it overheats in about ten minutes flat. The other two were about the same way - although the Jeep has had the most components replaced. The other two cars were "Point A to Point B" machines, and as long as they got me to and from work, I really didn't care.)

It behaves normally - except for the fact that I know that something is missing. I can't figure it out - as I said, everything has been flushed or replaced (save the heater core,) and I didn't see any scale buildup in the block jacket when I changed the water pump, either. Or inside the head form the thermostat changes. Granted, I don't have a fibrescope - so I can only check so far...

Well swapped out the renix to the HO radiators and a new thermostat so far it works great. Although I set it up kinda like a wrangler W/ AC. Just ran hoses directly to the heater core since I didnt have two t-vavles to divert flow to the heater core when Im using cool air. Luckily enough cool air is still plenty cool.

Ran into two problems.
1.) broken radiator and ac condenser mount. So we just used some old rubber padding 1/2" thick to make a new suport/mount.

2.) Broke the lower tranny cooler hookup. Wasnt sure how bad the break was so JB Welded it to be safe and bout a cheap tube and find tranny cooler.

So far it heats up to about 205*F and doesnt go past or lower. Also did the holes at 6 and 12 o'clock on the thermostat which alot of air came out as withnessed through the spout/neck. No antifreeze comming through the heater vents. Im happy now and warm.

Gonna check for leaks once more then call it good. Tranny cooler looked neat infront since its all clean. Also add some tranny fluid since I lost a couple ounces when I turned it on due to the damn ford quick change disconnect clips.

I'm going to guess the impeller is slipping on the new water pump, or somebody stuffed a tampon in the plumbing when you wern't looking!

5-90 said:

Yeah, it's one of three vehicles I've that that do not like thermostats. I've no idea why. (The other two were a 1985 Chevvy Cavalier with the 2.8L, and a 1980 Honda Accord with the 1800c/c CVCC.)

Oddly enough, it doesn't take any longer to get up to temp - not here in town, or up in the Sierras in wintertime. Heat works fine, gets up to temp quickly, and it doesn't have any complaints (unless I put in a thermostat again - every time I've tried that, it overheats in about ten minutes flat. The other two were about the same way - although the Jeep has had the most components replaced. The other two cars were "Point A to Point B" machines, and as long as they got me to and from work, I really didn't care.)

It behaves normally - except for the fact that I know that something is missing. I can't figure it out - as I said, everything has been flushed or replaced (save the heater core,) and I didn't see any scale buildup in the block jacket when I changed the water pump, either. Or inside the head form the thermostat changes. Granted, I don't have a fibrescope - so I can only check so far...

Click to expand...

XJoshua said:

No antifreeze comming through the heater vents. Im happy now and warm.

Click to expand...

Was your heater core leaking too or ??

Ecomike said:

I'm going to guess the impeller is slipping on the new water pump, or somebody stuffed a tampon in the plumbing when you wern't looking!

Click to expand...

Not that I can tell - and I've run across impeller slip before, and tend to check for it on new units... (Damn thing drove me batty first time I ran into it - about 15 years ago. I don't use off-brand water pumps for that reason anymore, either...)