Questions about transmission, fluids, springs, horsepower, and more

[FamilyFunWagon]

Is there a post for a must do mod list for new jeeps?

I noticed that my transmission has some built up oil around the transmission. It is hard to tell if it is leaking as there is no fluid on the ground in my garage. So it got me worried and wondering if I should put in a transmission cooler? Also, since i'm going to be doing that should I just upgrade the factory radiator?

• What coolant do you guys prefer?
• What transmission fluid?
• differential fluids?
• How can I safely get some more horsepower?

Also, how do I know if the springs and shocks are still good?

• is there a way to measure the length of the springs to know if they are too compressed?

I bought this used from a dealer, so i really don't know when these parts were installed.

I will take pictures and post them.

Sorry for so many questions, I am just trying to make sure I am being a responsible proactive Jeep Owner.

 

[FamilyFunWagon]

Here are the picture of the tranny and radiator.

 

[derekmac]

is there a way to measure the length of the springs to know if they are too compressed?

With the Jeep parked on a nice flat spot you can measure the springs (do not include the rubber isolator). Stock the front springs would measure 12", and 8" for the rear.

 

[Jerry Bransford]

For coolant most of us here use and recommend a 50-50 mix of Zerex G-05 and distilled water.

Your automatic requires ATF+4, any brand is fine. But if it doesn't say "ATF+4" in big letters on the front of the bottle it's the wrong stuff. Not even Mobil-1 ATF is the right stuff. Make sure yours is full and at the the transmission's dipstick full mark, it should not be lower than that. Measure it only while the engine is running (and warm) and in Park after you've shifted through the gears a couple times. Better to be slightly overfilled than underfilled. Make sure the ATF is clear and red, and not burnt smelling.

Any GL-5 gear lube is fine in the axles 80W-90 for light duty, 75W-140 if you tow. Your gears will run cooler if you run a conventional gear lube, tests have shown the gears to run hotter when lubed with a synthetic which is something I unfortuately learned first-hand.

There is no easy or inexpensive way to get more HP with the 4.0L engine, especially not with an aftermarket air intake system. If you're running bigger than stock tires that will really cause a loss of performance which is easy, though not inexpensively, fixed by regearing the axles to a lower ratio. What size tires are installed? Your 42RLE automatic transmission sets the engine rpms extra-low on the highway so performance is especially and significantly affected by larger than stock size tires.

 

[Steel City 06]

That leak could possibly be engine oil from the rear main seal, which is a common leak on TJs. If you can determine if it is engine or transmission oil, that would tell you what is leaking.

Here’s a guide on RMS replacement:
https://wranglertjforum.com/threads/rear-main-seal-replacement-4-0.826/
There is already a transmission cooler built into the radiator, though many owners install a supplemental cooler inline to provide additional transmission cooler. It’s not a bad idea, especially if you tow or do a lot of high speed driving. Most plate and fin coolers work great. Some companies like PSC offer bolt on cooler kits for one or two different fluids.

Very small HP gains can be had with various parts, like new heads, headers, etc. There are really only three ways to gain significant extra horsepower: Forced induction (supercharger or turbocharger), increased displacement and compression (stroker), or engine swap (V8). Several companies offer bolt in stroker/supercharger/turbocharger kits.

 

[FamilyFunWagon]

For coolant most of us here use and recommend a 50-50 mix of Zerex G-05 and distilled water.

Your automatic requires ATF+4, any brand is fine. But if it doesn't say "ATF+4" in big letters on the front of the bottle it's the wrong stuff. Not even Mobil-1 ATF is the right stuff. Make sure yours is full and at the the transmission's dipstick full mark, it should not be lower than that. Measure it only while the engine is running (and warm) and in Park after you've shifted through the gears a couple times. Better to be slightly overfilled than underfilled. Make sure the ATF is clear and red, and not burnt smelling.

Any GL-5 gear lube is fine in the axles 80W-90 for light duty, 75W-140 if you tow. Your gears will run cooler if you run a conventional gear lube, tests have shown the gears to run hotter when lubed with a synthetic which is something I learned first-hand.

There is no easy or inexpensive way to get more HP with the 4.0L engine, especially not with an aftermarket air intake system. If you're running bigger than stock tires that will really cause a loss of performance which is easy, though not inexpensively, fixed by regearing the axles to a lower ratio. What size tires are installed? Your 42RLE automatic transmission sets the engine rpms extra-low on the highway so performance is especially and significantly affected by larger than stock size tires.

It has 33" tires on it.

 

[FamilyFunWagon]

That leak could possibly be engine oil from the rear main seal, which is a common leak on TJs. If you can determine if it is engine or transmission oil, that would tell you what is leaking.

Here’s a guide on RMS replacement:
https://wranglertjforum.com/threads/rear-main-seal-replacement-4-0.826/
There is already a transmission cooler built into the radiator, though many owners install a supplemental cooler inline to provide additional transmission cooler. It’s not a bad idea, especially if you tow or do a lot of high speed driving. Most plate and fin coolers work great. Some companies like PSC offer bolt on cooler kits for one or two different fluids.

Very small HP gains can be had with various parts, like new heads, headers, etc. There are really only three ways to gain significant extra horsepower: Forced induction (supercharger or turbocharger), increased displacement and compression (stroker), or engine swap (V8). Several companies offer bolt in stroker/supercharger/turbocharger kits.

It looks like it has been damaged in the picture. What do you think?

 

[Jerry Bransford]

It has 33" tires on it.

Yes those are large enough to significantly reduce performance. The correct cure for that is to regear the axles to 4.88 or 5.13, though I'd go 5.38 if you think you might some day get to 35" tires. Those ratios may seem too low but they're actually correct for your particular transmission and they're what would work best for the street. Those are not "off-road" ratios though they will work well offroad too.

Regearing is not cheap but it costs less than a supercharger which would still have to work into an incorrectly geared Jeep whose engine is forced to struggle with the low rpms caused by the factory gear ratio inside your axles.

 

[Jerry Bransford]

For that leak, I don't see any damage. It's common for the rear main seal to leak if the engine has a synthetic engine oil in it. My BMW also had a RMS leak but I fixed that by replacing it with a conventional high-mileage engine oil that has extra seal conditioners. What worked well for me was Mobil Super 10W-30, I'd switch to that and it might just cure that RMS leak.

 

[Steel City 06]

It looks like it has been damaged in the picture. What do you think?

You wouldn’t be able to see the RMS from the outside. It is on the end of the crankshaft hidden inside the engine. You would have to remove the oil pan to access it.

What you are seeing is some sort of dust cover or splash guard (not sure of the name of it). That cover is not designed to retain oil.

If that is engine oil, it is most likely the rear main seal or possibly a leaking valve cover gasket. If it is the latter, you could reach around the back of the engine and feel it running down the block as well.

 

[FamilyFunWagon]

When I bought it from the dealer they said they had replaced the valve cover gasket because it was leaking. So, i didn't know if it was currently leaking or just old oil. I bought it from the Toyota Dealer in Escondido. There is not oil in my garage and I have had the Jeep for a couple of months now.

• Is it safe to take the scrape plat off and power wash that?
• In the picture of the radiator that bottom piece looks as though they plugged it with some sort of silicone and the yellow plug has antifreeze dripping from it. Do you guys think this could be an issue?
• I sometime smell coolant when driving. I noticed it was way overfilled when I bought it.

 

[FamilyFunWagon]

I found this receipt and it looks like the rear main seal was just changed about 1500 miles ago

 

[Steel City 06]

So it sounds like both of the most likely culprits were replaced recently. I would clean up the area with some sort of solvent or degreaser and wait and see if it is an active leak. Oil doesn’t evaporate easily, but it will flow if there is a leak.

 

[FamilyFunWagon]

Thank you guys for the help.
What transmission cooler would you recommend?
Do you recommend I change the Differential Fluids?

The gentlemen that owned it before me seems to have taken pretty good care of it. I actually found his number on a receipt and wanted to give him a ring just to get some background info on the Jeep. But I don't want to be that weirdo.

 

[MutantNinjaTJ]

replaced the valve cover gasket

They replaced the rear main seal and the oil pan gasket, not the valve cover, and it is probably the cause of the minor oil leak. I suggest Felpro kit with the bolt seals

 

[Steel City 06]

Yes, I would drain and fill the differentials. It will also give you a chance to check on their condition. You may also want to drain and fill the transfer case.

There are a few good older threads on the transmission cooler. Here‘s one:
https://wranglertjforum.com/threads...-transmission-cooler-on-your-wrangler-tj.590/
The PSC cooler setup also looks interesting:
https://www.pscmotorsports.com/vehi.../03-06-jeep-tj-lj/cooler-kits/psc-mbc100.html
I have a manual transmission so I don’t have experience with any of these coolers.

 

[FamilyFunWagon]

Yes those are large enough to significantly reduce performance. The correct cure for that is to regear the axles to 4.88 or 5.13, though I'd go 5.38 if you think you might some day get to 35" tires. Those ratios may seem too low but they're actually correct for your particular transmission and they're what would work best for the street. Those are not "off-road" ratios though they will work well offroad too.

Regearing is not cheap but it costs less than a supercharger which would still have to work into an incorrectly geared Jeep whose engine is forced to struggle with the low rpms caused by the factory gear ratio inside your axles.

Hey Jerry,
So, if I'm going to spend the money I should just jump to the 5.38. This jeep sits in my garage and I rarely take it out. Although I do plan on taking some camping trips with my kids soon enough.

Until then is it smart to click the OD off ?

 

[FamilyFunWagon]

I

With the Jeep parked on a nice flat spot you can measure the springs (do not include the rubber isolator). Stock the front springs would measure 12", and 8" for the rear.

Is there anyway to tell which Teraflex lift i have (as far as lift height)?

 

[Cross-Threaded-06TJ]

Hey Jerry,
So, if I'm going to spend the money I should just jump to the 5.38. This jeep sits in my garage and I rarely take it out. Although I do plan on taking some camping trips with my kids soon enough.

Until then is it smart to click the OD off ?

I'm not Jerry, but I would advise 5.38 gears also when you do. It's not as low as you would think when driving and it will work with 35's should you choose to go that route later. I have 5.13 gears and 35's and it is adequate. I have the same transmission as you but I do not have a Rubicon so 5.13 is as low as my Dana 30 front axle can go. Your Dana 44 front can go lower to 5.38 which will work with 33's or 35's. A touch low with 33's but still ok IMO.

I do advise a transmission cooler at some point soon. You can install the fancy Derale unit that is direct fit and goes underneath on the frame rail. Or install one on the V bars in front of the radiator.

I believe Jerry runs the Derale unit underneath and has a write up on it.

 

[derekmac]

I

Is there anyway to tell which Teraflex lift i have (as far as lift height)?

It looks like they have 2, 3 and 4" lifts. I don't know if there's a way to tell just looking at the springs though. They might have a P/N on them, but they might not.

Measure them, and post your findings.