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Old September 5th, 2009, 16:01
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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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