1998 Jeep Wrangler - Nuts & Bolts

    Four-, Six-, or Eight-Cylinder?
    I own a '98 Jeep Wrangler with 6 inches of lift and 33-inch tires. It is an automatic but has a 2.5L engine (120 hp and 140 lb-ft). I am ready for more horsepower because poking along on the highway just isn't working for me anymore. I am looking to swap my 2.5L for a 4.0L (181 hp, 222 lb-ft). Is this a good idea? Or should I go to a V-8? I can't afford to sell it to get a Jeep with a six-cylinder, so I have to do the swap and I would really appreciate the advice.Kurt RichardsonCleburne, TX

    The 4.0L engine swap will be much easier than any V-8 swap because the TJ was available from Chrysler with this package. But the costs involved with getting the 4.0L engine, transmission, engine mounts, and accessories for the swap could run you about the same amount of money as a small-block Chevy swap. That is, unless you have access to a donor Jeep. Remember there are people out there that swap the 4.0L out for V-8s. If it was us, and state emissions laws allowed it, we'd go with the V-8 swap and a TH700R4 that we could mate to the Jeep's NP231. Advance Adapters (800/350-2223, www.advanceadapters.com) offers bolt-in mounts for 350s (PN 713090), weld-in mounts for LT1s (PN 713005), and plate adapters (PN 713088-P) that can be used with PN 713090 to help you swap in an LS1 engine

    Thought He Had a Locker
    I have a '98 Toyota Tacoma SR5 without the TRD package, with the 2.7L four-banger that's in stock configuration. From what I have heard all Tacomas came from the factory with a selectable locker that engages when in four-wheel drive. I can put it in 4-Lo and get out in an open field or a parking lot and turn and the inner rear wheel will spin the same speed as the outer wheel (as a locked rear will), but sometimes when I get on a steep incline or get into another off-camber area, the rear locker will quit working. My friend also has a Tacoma and it does the same thing; the rear locker cuts out in the same places as mine. What could be causing this, and what will it take to fix it without taking it back to the Toyota place?Jacob Bartonby e-mail

    Sorry, Jason, but what you are describing are the habits of an open differential. You guys can't fix it because neither of your Tacomas has the optional rear locker. Not even all TRD package trucks come with it, and we don't think that it was ever available with the four-cylinder engines you have. Your first clue should have been that your truck doesn't have an On/Off switch for the locker on the dash. The TRD locker is not something that engages automatically.

    Keep Your NP208
    I own an '80 Ford F-150 4x4 with a 351 engine, a Dana 44 TTB frontend, and a Ford 9-inch rearend. It also has an NP208 transfer case. Is this a good transfer case? I know that all New Process transfer cases are good, but I would like to know how it stacks up against the other transfer cases. I have only owned this truck about a year, and I am only 15 years old, but I have never gotten stuck, even though I only do small-time four-wheeling. Also, I just bought a set of used 29/10.50-15 Super Swamper TSL SX tires. They are in good shape. How long will they last if I go four-wheeling with them and drive them on the highway?Jim VanLeeuwenWalnut, KS

    At your stage of the game the NP208 transfer case is fine. Don't waste any time worrying about upgrading to an NP205 or Atlas-that can come much later. You're lucky because your 208 should be one of the desirable bolt-on rear yoke versions that both Ford and Dodge used. While not as strong as a 205, it has a better low range (2.61 versus 1.96). New Venture Gear ditched the NP208 in GM and Dodge trucks by 1988, when it was replaced by the NP241, which offered an even better low range (2.72) and increased strength. Ford never used the NP241 in its trucks, instead opting to use Borg-Warner transfer cases. The Borg-Warner cases used an internal pump for better lubrication than the 205 or 208, but had durability issues because these pumps often failed.

    We can't tell how long your Super Swampers will last because we don't know how many miles are on them. Figure 20,000 to 30,000 total miles with very good care and frequent balancing and rotating. Since you're keeping your transfer case and running your used tires, you should be able to save some money for a set of 33s and a 4-inch suspension lift that will let you fit them. When it comes time to replace them, we'd recommend a radial mud tire because it sounds like this F-150 is going to be your only transportation for a while.

    High Speed Overheat
    I've got an '88 Jeep Grand Wagoneer that's mostly stock with 3-inch springs, 31-inch tires, 3.73 gears, and so on. The transmission is original but the transfer case is freshly rebuilt to original specs.

    My problem is that I have had the motor rebuilt twice in 10,000 miles. The original motor, with 129,000 miles, was tired and it overheated on the highway and spark-knocked under load at speeds over 50 mph. So a rebuild seemed in order. The "new" motor was strong, almost fast...well, strong anyway. But after 20 minutes at speeds over 65 mph, the temperature will start to climb into the red. It will also spark-knock terribly under any load/hill over 50 mph. I can't use the A/C at all without overheating on the highway. The odd thing is that I can spend all day in 90-degree heat on the trail, at speeds ranging from zero to 5 mph without the temperature moving up at all.

    I do have a winch that blocks a little bit of air into the grille, and I have removed the plastic air dam that I've heard will divert air to the motor. But in either case, this doesn't explain the cool temps at 5 mph off-road where most rigs are going to suffer. I've replaced every hose. The radiator is new. The water pump is new. The fan is stock. The fan clutch is new. I've used 160-, 185-, and 195-degree thermostats and even no thermostat.

    The culprit, I've heard, is the timing-it's over-advancing. But I've had countless mechanics adjust the timing but no progress. Help me!
    Mark Speece
    Atlanta, GA

    We agree that the toughest test for a cooling system is low vehicle speed and high load use, where there is very little airflow moving though the radiator. Which makes your dilemma that much more frustrating because low-speed operation is the only condition where your engine does not overheat. It seems like you've replaced everything that typically causes overheating, so as you suggested it could be an ignition-related problem. You've had the base timing set at idle, but have you checked to see how much total timing the engine runs when rpm increase and the mechanical advance comes in? Ask your mechanic to check this and verify that you are in the range of 30 degrees of total timing. If you're in the 40-plus degree range, you could be building too much cylinder pressure, which could cause piston-killing detonation and high engine temperatures.

    If the timing is in the ballpark, our next step would be to question whether the overheating gremlins might stem from improper engine assembly. The wrong (or improperly installed) head gaskets could limit coolant flow at higher engine speeds. Excess silicone sealer could have plugged up coolant passages, causing a restriction. And there is even a possibility that you are spinning the water pump too fast (wrong pulley), causing turbulence that leads to bubbles and air pockets at high speed.

    Submission information: Questions should be as brief and concise as possible. We will answer as many letters as possible each month, but due to the large volume of mail, we cannot send personal replies. Letters are subject to editing for length, as space permits. Always check state regulations before modifying a vehicle with pollution controls or one that will be driven on the street. Write to: Nuts & Bolts, 4-Wheel & Off-Road, 6420 Wilshire Blvd., Los Angeles, CA 90048-5515, fax 323/782-2704, e-mail david.kennedy@primedia.com