• NAXJA is having its 18th annual March Membership Drive!!!
    Everyone who joins or renews during March will be entered into a drawing!
    More Information - Join/Renew
  • Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

weak points of the 4.0?

rockshox

NAXJA Forum User
Location
CA
Im new to jeeps and I just picked up an 88 xj with 180k miles. Its got a 6.5" lift on 35s. Im considering replacing the motor with a reman engine for reliability concerns and Im wondering what mods I should consider beyond a stock rebuild. I dont plan on doing much hardcore crawling more like exploring the deserts of california and nevada. I was thinking arp fasteners and a high volume oil pump. I already ordered m.o.r.e. motor mounts. what else do I need to be aware of on this motor. thanks!
 
180k is nothing on this motor. I had one go 250k, and it only quit cause I hydroed it. The one I just bought has 208k on it and it runs without a tick.

If you are rebuilding it and dont want to swap to the HO, I would at least move to the HO head and intake/exhaust manifolds The high volume oil pump will require you to clearance the oil pan for it to fit. Search for "stroker" If you want to make a beast of a motor.

if this thread goes anywhere, be advised that no fewer than 4 people will post telling you to search, and that will be all they post. Keeps up the high falutin attitude while adding to your post count
 
Ive been reading but its hard to search on such a general question.

I can clearance the oil pan, I have a large hammer. And a stroker is out of the question.

If I want to go with the HO motor I just need new intake and exhaust manifolds and tb but otherwise I can use the renix ecu, flexplate, etc? Should I get an 88 block with the HO head or does it not matter? Is the HO just as reliable and torquey?

I dont really want to turn this into another renix vs ho thread, Im still wondering about the original question
 
The only Achilles heels that I know about is the alternator being mounted on the lower half of the engine and the exhaust manifold cracking, but those really dont have anything to do with the engine itself.
 
whompinxj said:
THE 4.0 DOESN'T HAVE ANY WEAK POINTS!
You fail.


Exhaust manifold.
Motor mounts.
Rear main seal.
Crappy intake system.
Im sure there are lots of others.



Replace the radiator, water pump, overflow bottle, and all coolant. Get a good oil filter and good oil. Upgrade the top end to a HO, and call it good after you fix the above problems.
 
CJ~Abuzer said:
The only Achilles heels that I know about is the alternator being mounted on the lower half of the engine and the exhaust manifold cracking, but those really dont have anything to do with the engine itself.

X2, especially the alternator. you're should be just fine. The 4.0 in general is a great motor.
 
My 88 has probably topped 300K by now - and I'm finally getting rid of the damned Peugeot transmission (been through four...) and I need to change out the engine management sensors. Engine still pulls strong and clean - and will do better once I get the sensors all changed out.

Weak points?
  • Lack of aftermarket support (especially for 1987-1990)
  • Cylinder head is relatively restrictive to airflow
  • Failing engine mounts can cause exhaust manifold cracks (there should be a flex joint between the manifold collector and the downpipe.)
  • Low-mounted alternator can be a problem with mud and water.
  • Vacuum-actuated front axle disconnect (1991-down, or thereabouts. You've got it, if you've got the NP231 transfer case with no full-time 4WD option.)
  • Early XJ's (1995 and earlier) are a bit under-braked - swap in a 1996-up dual diaphragm brake booster and associated master cylinder. Also, if you have ABS, plan on removing it.
  • 1987-1990 control electronics aren't available in anything else

Upsides?
  • Built by AMC - "All Makes Compatible." Most engine management parts are standard GM for the era
  • The AW4 automatic is rock solid. If you have the five-speed, it's the Peugeot - change it soon! However, the automatic is just great
  • While it's not a "wind-up and go" engine like in most other vehicles, the 4.0L will give you 90% or more of peak torque from ~1300-3500RPM. Ideal cruise is around 2800-3000rpm, which it can do all day long.
  • 1987-1990 control electronics very rarely fail (see above)

A high volume oil pump isn't necessary, and can cause trouble for you anyhow. I wouldn't worry about getting ARP fasteners unless you're overhauling the engine already anyhow - but there's no need to "just on account of 'cause" at 180Kmiles, assuming it's been treated well up to now. Even then, the AMC six is fairly tolerant of abuse, and so are the AMC chassis (I once pulled an 18K# load with my 1987. Didn't go fast, but I got it where it needed to go - from Morgan Hill to San Jose. I'm not sure I'd want to do it again, but it did it the first time. Why did I do it? The boss had the shop truck, and I needed to get that project going.)

Check your rear axle carefully - it could be either the Dana 35 (oval cover) or the Dana 44 (irregular hexagonal cover, "resting on a point.") The Dana 44 was a fairly rare option, and 1988 was the last year for it (domestically - it was available a bit longer in export vehicles,) but it's a damned solid axle and you'll want to keep it.

If you have any more specific questions, I'd be happy to help you. However, that's all that leaps readily to mind with an open-ended question like that...
 
For real, do a compression test.

I've been that deep into two RENIX engines, both have over 220K, both have cylinder pressures in the 130/135 PSI ballpark. The one I've done the most work on spins the 30" tire with it's open axle and stock gears.
 
My .02 , If you have the time and money, why not put a re-ring kit in it with a nice cam upgrade. Alot of people dont realize you can pick up and extra 15hp & 20'lb!! Total investment about 500, but hey... extra poneys and realability.. why not?!?
 
JoeOffRoad said:
My .02 , If you have the time and money, why not put a re-ring kit in it with a nice cam upgrade. Alot of people dont realize you can pick up and extra 15hp & 20'lb!! Total investment about 500, but hey... extra poneys and realability.. why not?!?

Makes sense - but if your compression is good, why do work you don't need to? A cam job is just enough of a pain on the 242ci/4.0L (because you have to remove the head) that you may as well overhaul the engine while you're about it.

Then, you can throw in a stroker crank (258ci/4.2L) and get a lot more than 15HP/20lb-ft...
 
ok I was kind of misleading out of embarrasment. the motor already has issues and needs replacing. I think after reading about renix to ho swaps ill just stick with the renix since I just want to get it running again.

thanks for the advice everyone and 5-90 thanks for the extra non motor tips. I see we are in the same city. My xj has a ford 8.8 rear axle already and an automatic so I think im ok on that

With the crappy intake system is it work getting a mild porting on the head or would I not see much gain without a better intake manifold and tb.
 
search........







yay.....my post count is 2,016!!!





The closed cooling system is another liability on the renix motor.That always starts a debate,though.
 
outlander said:
search........







yay.....my post count is 2,016!!!





The closed cooling system is another liability on the renix motor.That always starts a debate,though.

Damn right it do! Drill the thermostat as I've covered so often, and you don't get trapped air. There's nothing inherently wrong with the closed coolant system - my closed system ran cooler (by about 10*) than the 1989 I bought that was already converted when I bought it. Otherwise, the radiator is the flaw - and that's nothing to do with "open" or "closed" system, just component construction. OEM RENIX radiators (and some early HO, in fact) tend to clog up and fail at 150-180Kmiles, per local Jeep techs. Even they use aftermarket replacements - usually Modine (same brand I use.)

You can also source all metal CSF replacements from DPG offroad - who happens to be a NAXJA sponsor.

You don't really want to compare post counts, do you? ;)
 
rockshox said:
ok I was kind of misleading out of embarrasment. the motor already has issues and needs replacing. I think after reading about renix to ho swaps ill just stick with the renix since I just want to get it running again.

thanks for the advice everyone and 5-90 thanks for the extra non motor tips. I see we are in the same city. My xj has a ford 8.8 rear axle already and an automatic so I think im ok on that

With the crappy intake system is it work getting a mild porting on the head or would I not see much gain without a better intake manifold and tb.

Where in town are you? I'm not feeling up to scratch at the moment, but I'd be happy to help you when I can (five years of taking care of someone chronically ill has finally caught up with me - I'm sick with the crud. My mucous can be used as an industrial/structural adhesive, and it hurts to swallow anything tougher than Jell-O. Hell, even Jell-O hurts!)
 
some people must like replacing the plastic surge tank on the closed system every two years.....not to mention its just another part that will leave you stranded on the trail.
 
Back
Top