AbreedApart89South Posted September 9, 2022 Share Posted September 9, 2022 Good evening folks about 7-8 years ago and came across this 89 Jeep comanche that a feller sold me for 800$ needed a transmission everything was their hadn't been dogged some rust on the floor pans but all is well now it had like almost 400,000 and now around 456,000 hard on off road give or take a 1000 miles it being what I believe to be original motor. All that being said The 89 Jeep comanch straight six 4.0 Being the Renix or Renault/Benix AMC was Cast Iron Block and Heads?? Mine is doing a light knocking due to all the miles sounds like by the oil plug so a bearing or something I'ma drive it till it blows but I was looking at this place online called jegs that has a remanufactured one for right at two grand block and head and it says cast iron and y'all recken that be just as good as haven mine rebuilt.. I'd get mine rebuilt but the remanufactured afford like a 7 year warranty which is better then if I had mine rebuilt and in 3 years something happend no warranty vs up to 7 yrs what's y'all opinion or point me in the right direction please thanks much Link to comment Share on other sites More sharing options...
Eagle Posted September 10, 2022 Share Posted September 10, 2022 Yes, the 4.0L is a cast iron block and a cast iron head. Why not just drop the oil pan, replace the bearings, and keep driving it? Have you checked the compression? Is that 456,000 miles, or kilometers? Link to comment Share on other sites More sharing options...
AbreedApart89South Posted September 10, 2022 Author Share Posted September 10, 2022 456,000 miles. I have not checked the compression. It still runs like it did just with a light knock. Ive not thought about that. I assume by dropping it be obvious to see if it is a bearing? And can you just by them at your local napa O'Riley advanced auto parts place or need to be ordered? Thanks for the response and input Link to comment Share on other sites More sharing options...
Dzimm Posted September 10, 2022 Share Posted September 10, 2022 You'll probably have to order the bearings, stores don't carry much for older vehicles anymore. At least from my experience. Checking the compression is a great start and I'd even consider pulling the pan just to get eyes on underneath. If it was top end noise I wouldn't worry as much but bottom end is a little more serious. You could always take the route of thicker oil to make the knock go away and keep driving. Doesn't actually fix anything but out of... sound, out of mind? Link to comment Share on other sites More sharing options...
cruiser54 Posted September 10, 2022 Share Posted September 10, 2022 Auto trans? Harmonic balancer failing? Link to comment Share on other sites More sharing options...
Pete M Posted September 10, 2022 Share Posted September 10, 2022 11 hours ago, AbreedApart89South said: I assume by dropping it be obvious to see if it is a bearing? have you ever inspected crank bearings before? if not, I'd suggest a youtube vid to get a peek into what's required. Link to comment Share on other sites More sharing options...
AbreedApart89South Posted September 10, 2022 Author Share Posted September 10, 2022 Ok so I was reading other things on the club and started with the cheapest first turns out it was the Flex Plat THANK GOD however I still wanna change the oil pump it's never been changed at least sense I've had it.. the oil gauge reads about or between 40 and 80 like so just over the half line it doesn't burn or leak oil...should I change it or leave it be? Also I've got several wires under the hood and under dash I'm not sure what they are I seen someone post some pictures but I couldn't tell exactly what wires they are Link to comment Share on other sites More sharing options...
AbreedApart89South Posted September 10, 2022 Author Share Posted September 10, 2022 And much obliged for all the help my Jeep is my daily driver so I try to baby it and do everything I can to keep it jeepen Link to comment Share on other sites More sharing options...
89 MJ Posted September 10, 2022 Share Posted September 10, 2022 If it makes good oil pressure (I believe 20lbs at hot idle is considered sufficient), I would leave it. No sense in spending unnecessary money, and the newer aftermarket parts tend to fail quicker than OEM do. Link to comment Share on other sites More sharing options...
cruiser54 Posted September 10, 2022 Share Posted September 10, 2022 Leave it alone!! You came real close to doing a big job unnecessarily as it is. Link to comment Share on other sites More sharing options...
Eagle Posted September 11, 2022 Share Posted September 11, 2022 20 hours ago, 89 MJ said: If it makes good oil pressure (I believe 20lbs at hot idle is considered sufficient), I would leave it. No sense in spending unnecessary money, and the newer aftermarket parts tend to fail quicker than OEM do. Actually, 13 psi at hot idle is the minimum factory spec. Link to comment Share on other sites More sharing options...
AbreedApart89South Posted September 11, 2022 Author Share Posted September 11, 2022 Okay left alone it will be and yes I'm very greatful it was the Flex Plat and not the bottom end and my oil pressure gauge reads 0 - 40 - 80 but the hand stays a little over 40 when running Link to comment Share on other sites More sharing options...
Eagle Posted September 11, 2022 Share Posted September 11, 2022 9 minutes ago, AbreedApart89South said: my oil pressure gauge reads 0 - 40 - 80 but the hand stays a little over 40 when running 40 at idle, or 40 at highway speed? It should be higher at highway speed. 40 at idle would be good for a NEW engine. Link to comment Share on other sites More sharing options...
AZJeff Posted September 11, 2022 Share Posted September 11, 2022 I will elaborate on what Eagle said about oil pressures. The 4.0 engine has "official factory approved" oil pressures of 13psi minimum at idle, and above 1600 rpm, it should be between 37 and 75psi. These numbers are, of course, with factory recommended 10w30 oil and with a hot (fully warmed up) engine. I think the reason the pressure range is so wide when measured at 1600+ rpm is because, in my experience, there is a pretty broad range of oil pressures reported by various owners with the 4.0 For example, on my MJ, the hot idle oil pressure is about 23psi, which is well above factory minimums. However, that same engine, when it gets fully hot (and I mean REAL hot here in Phoenix) only puts out about 42psi at 1600 rpm, which is at the low end of recommended. Another factor to consider, and this is just my personal opinion, and not backed up by any data, is that the 4.0 isn't an engine that is extremely demanding of high oil pressures to function as expected. in other words, as long as your engine is making steady oil pressure, the engine is fine with a pretty broad range of oil pressure values. Link to comment Share on other sites More sharing options...
AbreedApart89South Posted September 11, 2022 Author Share Posted September 11, 2022 1 hour ago, AZJeff said: I will elaborate on what Eagle said about oil pressures. The 4.0 engine has "official factory approved" oil pressures of 13psi minimum at idle, and above 1600 rpm, it should be between 37 and 75psi. These numbers are, of course, with factory recommended 10w30 oil and with a hot (fully warmed up) engine. I think the reason the pressure range is so wide when measured at 1600+ rpm is because, in my experience, there is a pretty broad range of oil pressures reported by various owners with the 4.0 For example, on my MJ, the hot idle oil pressure is about 23psi, which is well above factory minimums. However, that same engine, when it gets fully hot (and I mean REAL hot here in Phoenix) only puts out about 42psi at 1600 rpm, which is at the low end of recommended. Another factor to consider, and this is just my personal opinion, and not backed up by any data, is that the 4.0 isn't an engine that is extremely demanding of high oil pressures to function as expected. in other words, as long as your engine is making steady oil pressure, the engine is fine with a pretty broad range of oil pressure values. Well I appreciate the information y'all I reckon my Jeep is doing all it should running gear wise. Thanks again Link to comment Share on other sites More sharing options...
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