What straight wt oil to try for 2000 RHD Cherokee

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Have a 2000 RHD Cherokee (200K miles) that got hot on mail route and oil pressure went away (this was a few years back,radiator blew). Been getting by with 15 40 Synthetic in winter, regular 15 40 in summer. In both cases a bottle of STP added. The oil light has started to come on at idle after it is warm. Some one suggested going to a straight weight. Don't want to start thin and waste it. Don't want to go too thick to begin with. Whats your best guess on the weight I should try first. Thanks.

It is used as a back up vehicle now so not driven all the time. The oil light started coming on this winter.
 
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If the oil light is coming on with 15W40 in it, no monograde/straight weight short of a 50 is going to make any difference. At operating temp, a 15W40 and a monograde 40 are just about the same. I think the advice that you received is uninformed...

So, best guess? Try something like the Valvoline racing 50 for a monograde...but it's going to be awful trying to get it started in cold weather...I think your best bet is to bump up to a 20W50 multigrade...any brand will do...easier starts, slightly higher viscosity than the 15W40 you're running.

It's worth putting a known/calibrated oil pressure gauge on this when it's hot...would be nice to know what your actual pressure is...instead of trusting the idiot light. Given the age/history, your bearings are likely very worn...and nothing short of a rebuild is going to fix this permanently.
 
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200K? Verify the sending unit and oil pressure with a mechanical gauge. If low, replace the oil pump.

It's $60-$70 and you can upgrade oil pan gaskets to the one piece as well (rear main is right there too). I did one on a New Hampshire house call on the ground in winter. It took me 4 hours.

If you're not interested in looking into it/repairing correctly, as I suspect because it happened a few years ago, then just drive it. SAE50 might help in summer, but is a silly bandaid IMO, as lubrication will suffer just to keep an idiot light off.
 
I agree that you need to verify the problem. Electric oil pressure senders are not trustworthy. Even new ones are sometimes inaccurate. A mechanical gauge should be used to verify what the pressure really is when the light is coming on.

If that's not an option, and you have to trust the sender, then at least make sure you're using the proper OEM spec sender (Mopar or whatever label they use now. I've had major accuracy problems with knockoff brands on GMs anyway). But if you can, a mechanical measurement is 100x more meaningful than any replacement sender.

Assuming the pressure problem is real, then I'd suggest 20w50 to nurse it along, and be easy on it. If it starts knocking, it's done and the damage will accelerate quickly. In that event definitely stop driving it until you can get it rebuilt.
Also consider the possibility that the previous overheating may have blown a head gasket (maybe worse, especially if it's an aluminum head). There could be slow contamination that's thinning the oil.
 
As Zaedock and armos have suggested, you may be fixing a problem that does not exitst. Your pressure may be fine, at that mileage replace the sender.
 
Originally Posted By: armos
If that's not an option, and you have to trust the sender, then at least make sure you're using the proper OEM spec sender (Mopar or whatever label they use now. I've had major accuracy problems with knockoff brands on GMs anyway). But if you can, a mechanical measurement is 100x more meaningful than any replacement sender.


Yeah, forgot to mention this ^^^

In my experience, cheap replacement sending units are just that, cheap!
 
Originally Posted By: LargeCarManX2
Chevron Delo 400 30w and add a can of STP

or

Amsoil 60w motorcycle oil


I had a lot of Delo SAE30 and 15W40 from the '05 sale. The SAE30 is on par with a 15W40 when cold and is 12.1cST @ 100*C when hot, thinner than the 15W40.

I also wouldn't put Amsoil anything into this engine $$. Supertech all the way!
 
I agree you need to find out if its really low oil pressure with a mechanical gauge. But given your scenario it certainly may be. Certainly an oil pump is worth trying.

After that I think you are looking at a rebuild. Does it also burn oil?
 
If I were trying to nurse along such a vehicle, I'd see if I could get some Penrite HPR30 20w-60. According to Penrite, it's available in the US, and should give better cold-start performance than a heavy straight grade.
 
First, actually check oil pressure with mechanical gauge, or replace the cheap sender.
If pressures good, replace sender.
Then, move on to the oil pump. Under $100 including refreshing several gaskets.
 
I'v changed the sender twice, it has a gauge also. Will have checked with mechanical gauge. Light just started coming on. Mail delivery vehicle so has a ton of idling time on it (5 hours to a hundred miles). Just called my NAPA and told them to bill me for a case of 15w50. No rattles, even when light on. Rattles good on startup though. Been a good one. You think new oil pump will help if pressure low.
 
You guys are on the wrong track with the right idea.
wink.gif


OP needs to either pull his thermostat or put in a 150-160 degree one. This will thicken up the oil more than going up a grade. Those jeeps have a mechanical and electric fan, IMO. Wire up the electric to be always on.
 
On a 2000, the head probably cracked when it got hot (0331 head). Has it been losing coolant? If so, the bearings in the bottom end are probably shot if it's got low oil pressure, as the coolant has likely wiped them out.

If the oil isn't milky, no slime under the oil cap and it hasn't been losing coolant, then verify the pressure with a mech gauge and replace the oil pump if it's actually low (worn out oil pumps aren't uncommon on high mileage 4.0s).
 
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