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  #1  
Old September 5th, 2009, 12:35
SFW516 SFW516 is offline
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Renix Cooling Tips

First off I really appreciate all the great help I have gotten from everyone on the board. It has really helped alot.

I have a 90 xj with the original cooling system arrangement that seems to really not work to good. Any recently got a new radiator and overflow bottle on it. Also replaced the thermostat with the same temp rating, 95 degrees I believe. So now on hot days and around town the thing still heats up pretty good. I was wondering if there are some easy things I can do to cool it off a bit. Is it recommended to put a lower temp thermostat into it? I noticed that my electric fan seems to only come on when I turn the air on. Is that normal? Has anyone wired these to just stay on continually to bring temps down?

Any advice would be great. Thanks.
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  #2  
Old September 5th, 2009, 13:11
lawsoncl lawsoncl is offline
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Re: Renix Cooling Tips

It is possible that the switch or relay for the electric fan is bad?
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  #3  
Old September 5th, 2009, 13:42
Slip Kid Slip Kid is offline
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Re: Renix Cooling Tips

If it really is getting too hot and not turning on the fan, the switch in the rad is probably bad. I don't remember when it's supposed to turn on, but it's pretty high, below actually running hot but above what some people consider running hot. I would not use any thermostat except a stock temp one, as it runs best at the proper temp.
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Old September 5th, 2009, 16:32
SFW516 SFW516 is offline
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Re: Renix Cooling Tips

Yeah as far as the thermostat goes that was what I was thinking too. I don't want to stray from stock and get into trouble. Does anyone know where the relay for the fan is located? Do you know of any wiring diagrams for that circuit?
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  #5  
Old September 5th, 2009, 17:01
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5-90 5-90 is offline
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Re: Renix Cooling Tips

It's common for the RENIX radiators to get clogged up (OEM) - the service life for them seems to be 150-180Kmiles, per the local Jeep service techs. Even they replace them with Modine or Performance Radiator (both aftermarket brands, both that I've used with good results as well,) and forget about them. That may be something like the trouble you're having.

Most "open conversions" fix the actual problem without realising they've done so - simply by replacing the radiator.

OEM thermostats are 192-195*, but can safely be replaced with 180*. This doesn't really lower the operating temperature of the engine (210-215*F,) but it does get coolant flowing much sooner.

The electric auxiliary fan is supposed to come on when one of two things happens: 1) The Thermal Fan Switch (TFS) closes, which engages the relay and turns the fan on (the TFS is in the driver's side radiator tank.) I believe this is supposed to happen somewhere around 220-225*F, and turn back off somewhere around 200-205*F. 2) The air conditioning is turned on, which sends out an AC REQ signal which engages the relay.

The relay is located on the driver's side fender liner, and is a standard Bosch/Hella DIN item. It should be available pretty much anywhere for ten bucks or less. They're all over the XJ, so they're something you should keep one or two of in your spares box anyhow (with your fuses and small lamps.)

You can test relay function by disconnecting the TFS from the harness, and using a small jumper wire to bridge the pins on the harness end of the connector. The fan should turn on, so watch your paws! If it does not, reconnect the harness plug. Go make a small jumper out of about 6" of 14AWG wire (or larger) and two 1/4" male unshrouded spade connectors. NB: This test should be done KOEO - Key ON, Engine OFF. If the fan comes ON, replace the TFS.

Pull the relay, and look for the numbers moulded into the base, next to each pin. Take your jumper lead, and insert one spade into the socket terminal that corresponds to relay pin 30, and the other end into pin 87's socket. The fan should turn ON (you're still doing this test KOEO.) If the fan comes on with this test, replace the relay.

If the fan still doesn't turn on, use two long jumpers with alligator clips (and at least 14AWG wire) to jump the fan directly to the battery. Doesn't matter which way - if you get the polarity reversed, the fan will spin backwards - but you'll still verify function. If the fan doesn't spin in either direction, replace the fan module (use a 1996-up fan, as it's more efficient.)

If the system hasn't been flushed in a long time, consider doing the "two-part" flush - the first part is oxalic acid to really break things loose, the second part is a neutraliser for the acid. Then, use a mild flush every alternate year, and replace the coolant (used coolant can usually be taken to any shop that does automotive cooling system work - they usually have a guy who comes around and recycles it for them on-site. I've never been charged for dropping it off at my local shop.)

Fan clutches are typically good for about five years in the XJ - consider replacing that as well. Write the date on the new one when you put it in, makes it easier to keep track.

For having an override switch for the fan, it's really quite simple. Get a set of two-pole "Weatherpack" terminals (just like on the TFS) from the local, and a length (eight feet or so, I think) of 18/2 SJOOW rubber-jacketed wire from the hardware store. You're going to wire the Weatherpacks as a short jumper to go between the harness and the TFS, with the 18/2 splitting out of one side. Run the 18/2 to the IP to a convenient location, add a switch, and you've just added a third way for the e-fan to turn on (without having a lot of high-current electric running about.) The relay will now close when one of three things happens - the TFS closes, the AC REQ signal is sent, or the switch you've just installed is closed by you. And, the fan will turn off when you turn the key off, so you won't have to worry if you leave the switch on. Simple, no?
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  #6  
Old September 5th, 2009, 21:33
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Ecomike Ecomike is offline
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Re: Renix Cooling Tips

I have done some extensive data collection on the 87-90 cooling systems and found some interesting things. First you need to distinguish between the thermostat housing temperature (180 to 220 F depending on T-stat choice and heat load) which is the maximum coolant temperature and the radiator exit coolant temperature where the Renix ('87-'90 years) XJs TFS is located. When I installed a new aluminum 2 row radiator 4 years ago with a new TFS the fan switch tripped on at a radiator outlet coolant temp of 175 to 180 F and off at 160 -165 F.

Then earlier this summer my jeep was overheating long before the TFS got hot enough to turn on. The problem turned out to be that the radiator flow was comprimised after just 4 years, and the coolant was flowing slowly through the radiator, getting down to 170 F, not tripping the e-fan, but the coolant was getting way to hot coming out of the engine. I tried a new water pump, new thermostat, hot wired the efan, a new ZJ fan clutch ( basically a HD XJ fan clutch), and a new 3 row copper/brass CSF radiator was the last desperate thing I tried, and only the new radiator solved the problem.

With the 4 year old radiator I had a 40 F delta T across the radiator, which was deceptively looking like a good radiator. Problem is I had no way to measure flow rates. Now the new radiator has only given me a 15 F delta T, but the jeep does not overheat now with the new radiator.

So WTF!

Conterintuitive, but what has happened is the new radiator seems to have 3-4 times the flow rate as the older one, and while the Delta is lower, it is removing more total heat that before (Q= Mass rate times the delta T). Also the exit temperature of the new radiator is hotter than before, so my TFS for the e-fan comes on sooner now (another deceptive surprize to our prior analysis)

Needless to say, this was all a real big surprise to me, and should be to most of us here!!!! I know I had everyone here scratching their head over my recent problem.
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Last edited by Ecomike; September 5th, 2009 at 21:39.
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  #7  
Old September 5th, 2009, 22:16
SFW516 SFW516 is offline
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Re: Renix Cooling Tips

Thank you very much for all the helpful advice, I will do some more investigation on the fan first and get back to you. I have a feeling its either the relay or the sensor. So if I do put in a 180 thermostat it won't cause any problems? I just might do that if it continues to run warm.

The thing is everytime I open it up and take a look the upper radiator house is always pretty stiff and there is a good bit of pressure build up on the overflow bottle. So much so that it will spew coolant if I open it up. I just think if I let it continue it will damage the overflow for sure and who knows what else.
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Old September 5th, 2009, 22:25
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Re: Renix Cooling Tips

It did sound like the TFS was dead on yours, and the relay is OK.

5-90 and I have run 180 F T-stats on ours for years on 87-90 models.

The 195 F T-stat is recomended on the newer XJs, especially 96, OBD-II and newer, as the the PCMs are anal about the CTS reaching a certain temp to go closed loop on the O2 sensor fuel injection operation, while the Renix (87-90) will go closed loop at room temperature.
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  #9  
Old September 5th, 2009, 23:06
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5-90 5-90 is offline
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Re: Renix Cooling Tips

Quote:
Originally Posted by SFW516 View Post
Thank you very much for all the helpful advice, I will do some more investigation on the fan first and get back to you. I have a feeling its either the relay or the sensor. So if I do put in a 180 thermostat it won't cause any problems? I just might do that if it continues to run warm.

The thing is everytime I open it up and take a look the upper radiator house is always pretty stiff and there is a good bit of pressure build up on the overflow bottle. So much so that it will spew coolant if I open it up. I just think if I let it continue it will damage the overflow for sure and who knows what else.
It's going to spew coolant. Water boils at 212*F at STP, but that point is increased by 3*F for each psi of pressure added above atmospheric (14.7psia.) So, if the pressure is 15.7psia, water will boil at 215*. 16.7psia? 218*F.

RENIX caps are spec'd for 13-16psig, or 1ATM (14.7psia) + 13-16psi, or 27.7-30.7psia. Round up, call it 28-31psia (close enough for illustration.) At 3*F per 1psi increase, you're looking at an increase of 39-48*F increase, or a new boiling point of 251-260*F.

When you remove the cap, you effectively remove that pressure - and the water (210-215* design operating temperature) is now allowed to boil freely. Recall that "antifreeze" serves to lower the freezing point of coolant, but does little for the boiling point - that's done by the system pressure.

So, it's no surprise that your coolant starts boiling as soon as you remove the cap - that pressure (that you've released) is the only thing that prevented it from happening in the first place!

If you want to play with the fan actuation temperature, there are some adjustable sensors that will fit a 3/8" NPT port, and you can replace the RENIX thermostat housing with an HO version (same shape, but adds a 3/8" NPT port for a sensor that the HO uses but the RENIX does not.) Leave the RENIX TFS in place as a plug, and that takes care of that hole. You'll want to get a sensor that can be adjusted for an "ON" range of 215-230*F, and an "OFF" range of 190-195*F or so. These are actual, absolute values - I'd forgotten to mention that the values given earlier were "relative" values, and the actual operating values for the TFS are somewhat lower - to reflect its position in the "cold-side" radiator tank.
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  #10  
Old September 5th, 2009, 23:26
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90Blue_XJ 90Blue_XJ is offline
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Re: Renix Cooling Tips

The newer style T-stat housing when placed on a Renix engine, can use that extra plug as a bleed for air removal from the system w/o going the temp sensor in the head removal route. This also avoids putting the rear wheels on ramps too.
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