TECHLINE

COMPILED BY VERNE SIMONS EDITOR@FOURWHEELER.COM

MYSTERIOUS SENDING UNIT

I have a ’97 Wrangler TJ with a 4.0L that developed an antifreeze leak on the driver side of the block. Upon further investigation, we found the leak was coming from a sending unit (it looks like a pressure sensor) attached to the block with a 90-degree elbow. I believe the 90-degree elbow was added to keep the sensor from hitting the exhaust pipe. We took the pressure sender out and plugged the 1⁄8-NPT hole in the elbow, which solved the leak problem. The pressure sender was attached to a seemingly factory wiring plug that went into the wiring harness above it.

The question is: What is the switch/sender for? I have looked at various wiring diagrams and can’t find a coolant pressure sender on it. I even contacted a national call-in show who replied that they had replaced over 500 Jeep 4.0Ls and never seen a coolant pressure sender. Even the local auto parts store doesn’t have a listing for a coolant pressure sender. The sender that came off looks to be a PS284 sender but is denoted as an oil pressure sender in the literature.

I have read about dealer installed A/C systems and think this sender was used to turn off the compressor in the event of an overheating condition. The only time I have seen a water pressure sender is on my jet boat. I have looked at various Jeep blogs and can’t seem to find any reference to a water pressure sender. The engine didn’t throw any codes when the sender was removed and seems to be running fine.

A real head scratcher! Your knowledge would be appreciated.

DAN

VIA EMAIL

I agree with your assertion that what you showed us looks like an oil pressure sending unit or switch, and how it got into the 1⁄8-NPT port on the side of the block with an elbow is a mystery … and the wiring that you say goes into the harness is a real and true mystery. I had an initial gut reaction, and right or wrong, I am sticking with it. I’ve been wrong before, and by golly, I will be again!

But first, know that I did ask a few other well experienced Jeeple who might have some insight into this odd situation. One such person is Trent McGee, who is my pal and knows wiring (he runs Wicked Wiring in Glendale, Arizona) and he knows ’97 Jeep Wranglers well. He has a ’97 TJ buggy with a 4.0L and has spent time with it and a factory service manual (FSM) paring down the factory wiring, removing stuff not necessary on a buggy. He confirmed my suspicion that there is no indication of any kind of water pressure wiring in the FSM. His conclusion is the same as mine (below).

Chris Durham of Chris Durham Motorsports in Pickens, South Carolina (cdmracing.com), has seen several East Coast ’97 TJs and found this as strange as the rest of us, but came up with another plausible explanation: That sending unit that sure looks like an oil pressure sender could be a temp sender or temp switch to control an aftermarket electric fan. That’s similar to your idea that it could be related to an aftermarket or dealer installed A/C system, but for the life of me I can’t find a temp sensor or switch that looks like the one you describe.

Lastly, we chatted briefly with Jim Repp who worked for Chrysler to confirm our assumptions. He agreed with us that whatever this is, it is not from the factory and certainly added after the Jeep left Toledo.

At the end of the day, I could imagine a situation where for some reason the 1⁄8-NPT port in the driver side of the block started leaking and the oil pressure sender and elbow were the only items handy to plug the hole, but that doesn’t explain the wiring, and these threaded ports rarely leak to begin with unless messed with. Still, I’m gonna run with this as the most plausible explanation for what you’ve seen, a jury-rigged repair, though I could be wrong. The only other sound explanation is that the sender is a temp sender or switch related to an electric fan or some early aftermarket A/C system. Maybe a Four Wheeler reader has an idea about this and can tell us what the heck is going on here, but we can’t believe an oil pressure switch or sender would do much other than eventually leak when plugged into the water jacket.

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I wanted to pick your brain on the Shrink Ray TJ if you don’t mind answering a few questions. I’m thinking out my next build and want to do something similar. In one of your articles you mentioned if you could do it again you might use a TJ with a 2.4-liter. What are your thoughts on the 2.4L with the 42RLE and a Rubi-Crawler? I have no experience with four-cylinder Jeeps so I’m not sure if the auto will suck too much power from the engine. Are there any other changes you would make if you built it again?

After wheeling a stock-ish CJ-3B all over Texas and Moab, I’m convinced the idea behind Shrink Ray is a winner. It’s not as sexy as tons and 40s, but it works. Now the problem is finding a builder that will do this work.

CHRIS

VIA INSTAGRAM The Shrink Ray TJ was a fun rig to build, and a formula that really seemed to work well. Keeping things smaller is easier on parts and it’s easier to shed weight than to make more horsepower (in most circumstances).

To review, the Shrink Ray TJ was a build-up I did while at our sister “Jeep only” publication, Jp Magazine, back when it was still in print. The build idea was to take a beater TJ and instead of making it larger, make it shorter, shrink everything down, and focus on decreasing weight. The Jeep originally ran 33-inch tires, but we settled on 35s later on, and that was a pretty good balance of tire size, weight, and strength. We did this by swapping the steering box to a forward-sweep JK box and shortening the front until the Jeep had a negative approach angle. We also chopped the back to keep the departure angle down, kept the Dana 30 front axle, but added an 8.4-inch 2WD V-6 Tacoma (non-PreRunner) rear axle, and put the Jeep on a diet. In the end, Shrink Ray was (and still is) anvil-simple, and took years of beatings, including participating in the 2017 Ultimate Adventure, without many issues. Still, there were a few things we would do differently with the build if we had it to do over again.

For one, it could work to start the build with a later TJ, one with the more modern 2.4L fourcylinder. It’s the same dual overhead cam engine with four valves per cylinder that came turbocharged in the Dodge Neon and Chrysler PT Cruiser. That means that the engine can also be turbocharged. Chris Durham from Chris Durham Motorsports (CDM) did this a few times, though he started with a turbo Neon engine rather than modifying the Jeep 2.4L and was able to build a lightweight Jeep that made way more power than our old AMC 2.5L four-cylinder. This was something that we thought about while enjoying Shrink Ray. The 2.4L is a bit more modern and offers more power, though it may not be quite as durable as the old AMC 2.5L four-cylinder.

Also, as you mention, and as we have discussed in the past, swapping the factory AX-5 transmission for an SM420 gave the little Jeep awesome gearing off-road, but the on-road performance suffered because we lost the overdrive gearing and the gap between Second to Third gear was huge, meaning that we had to rev the little AMC four-banger pretty high to accelerate down the road. Also, it would probably have been better to swap the transfer case from the stock (albeit built) NP231 to something like a four-speed Atlas 2 transfer case from Advance Adapters (advanceadapters. com). That would have given all the gearing we could have used. Another alternative would be to have a 2.4L-powered TJ with the 42RLE with an Advance Adapters Rubi-Crawler, as you mentioned. That would give gobs of gearing and an overdrive, but we are guessing those Jeeps (2.4L with an automatic transmission) are rare. Also, the 42RLE, like all automatics, will suck some power, but the combination would be awesome with the Rubi-Crawler.

Other things that we could have and maybe should have done with Shrink Ray would be to have gutted the HVAC system to save weight. Also, we could have dropped the steel hood and front fenders for a fiberglass hood with mini-fenders molded in, like the hoods from Chris Durham Motorsports. A person could also probably shave more weight from the Jeep with air shocks, more sheetmetal trimming—basically building a buggy out of a TJ. Still, the Jeep did its job admirably and as far as we know is still out there putting around. It was pretty amazing what that Jeep could do even with the stock-ish short arm suspension and a few smart modifications.

Lastly, if you wanted to take the idea further, you could build a Shrink Ray-inspired CJ-5 or flatfender with an AMC 2.5L four-cylinder or DOHC 2.4L, a more modern transmission, and one of the gearing combinations mentioned above. You could build it with a tube chassis to decrease weight but maximize strength and keep the suspension simple and lightweight. I’ve also contemplated building another Shrink Ray out of a two-door JK. There is a ton of room for weight savings on that platform, as well. If you need a builder, are patient, and have some money to spend on the idea, I’d build that for you. FW

AFTER WHEELING A STOCK-ISH CJ-3B ALL OVER TEXAS AND MOAB, I’M CONVINCED THE IDEA BEHIND SHRINK RAY IS A WINNER.

COMPILED BY JERED KORFHAGE JERED.KORFHAGE@FOURWHEELER.COM

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