So it seems there has been a rash of low oil pressure problems in this forum over the last few weeks... I'll add mine. I'm a self-taught DIY'er, decent with a wrench but not a pro, and I feel like this forum has saved me tons of time and money, so hoping you guys can do it again.
My son who is away at school drives the '99 TJ. It has 215k on it, and we bought it with 185k. Recently he noticed the oil pressure running "low", and while he was home this weekend he showed it to me. I just about crapped my pants where I stood, because it was really low. It was sitting around 10, but it responds to increased rpm's and holds 30-40 psi under normal driving conditions. This change is unrelated to any recent maintenance on the vehicle - last oil change was in May, nothing else of note recently. There have been no indications of any mechanical problems with the jeep, and in fact it got great gas mileage on a recent weekend trip with mostly highway miles. It has a good oil level, and the oil looks clean (i.e. not milky, not dirty).
I went immediately to the Zone and got a replacement sending unit, as my first hope of "fixing" the problem. Installed it, and when the engine first cranked the gauge came up and read around 30 at idle, so I thought we just had a bad sensor. I left the old one sitting with the threaded end pointing up, and after 15 minutes I found a little oil that appeared to have drained out of the electronic side at the electrical connector. I took that to be confirmation that the diaphragm was damaged and causing a low reading.
Well, the boy drove back to school (roughly 2 hour drive) and called to say that when he stopped for gas, it had gone back to reading low at idle. This is not the kind of thing I want to hear at 9 p.m. on a Sunday evening. Immediately came to WF and did a search... which confirmed my fears. Apparently because we let the engine (and oil) cool off before replacing the sending unit, the good pressure at idle was just because the oil was a little thicker. Once it warmed up, it flowed more freely and thus the lower pressure.
We are going up to see him next weekend, so I'm planning to put a mechanical gauge on it to see how it looks. I believe it's likely the oil pump because it changed fairly suddenly and I don't think bearings would do that. However, based on the comments I've seen here, it looks like I would be well-advised to change them because we don't know for sure it's the pump, and "while we're in there" ....
My questions for the gurus here:
- first and foremost, I told him he needs to not let it idle with low pressure. If I read things correctly, as long as he keeps it above 13 psi, he should be okay (also watching to make sure it follows the 10 psi/1000 rpm rule of thumb). Is that correct?
- I see there's a high-volume (not high pressure) pump available at a slight premium in price, so is that a good idea?
- I saw mention of "oversize" bearings, assume that's to cover the possibility of excessive wear. Looking online, I only see "undersize" bearings listed (both main and rod). Assuming that's just a terminology difference. Should I use plastigauge first before buying, so I know for sure the correct ones to buy? If so, should I do each bearing separately, or should one be representative? It appears the sets are sold together all one size, so I would need to find the range of existing clearances and find the best match.
- where's the best resource for specs on clearances, torque? I've found sections of the factory service manual available on Scribd but never found a downloadable pdf copy... really like that format best if I can find it.
It's a bit overwhelming thinking about having to do all this on the engine, so I'm hoping I just got a bad sending unit and the mechanical gauge shows good pressure with the engine warm at idle. After my weekend (college and pro teams both lost) I'm betting I won't be that lucky...
If you've read this far, THANKS! Words of wisdom are greatly appreciated!
My son who is away at school drives the '99 TJ. It has 215k on it, and we bought it with 185k. Recently he noticed the oil pressure running "low", and while he was home this weekend he showed it to me. I just about crapped my pants where I stood, because it was really low. It was sitting around 10, but it responds to increased rpm's and holds 30-40 psi under normal driving conditions. This change is unrelated to any recent maintenance on the vehicle - last oil change was in May, nothing else of note recently. There have been no indications of any mechanical problems with the jeep, and in fact it got great gas mileage on a recent weekend trip with mostly highway miles. It has a good oil level, and the oil looks clean (i.e. not milky, not dirty).
I went immediately to the Zone and got a replacement sending unit, as my first hope of "fixing" the problem. Installed it, and when the engine first cranked the gauge came up and read around 30 at idle, so I thought we just had a bad sensor. I left the old one sitting with the threaded end pointing up, and after 15 minutes I found a little oil that appeared to have drained out of the electronic side at the electrical connector. I took that to be confirmation that the diaphragm was damaged and causing a low reading.
Well, the boy drove back to school (roughly 2 hour drive) and called to say that when he stopped for gas, it had gone back to reading low at idle. This is not the kind of thing I want to hear at 9 p.m. on a Sunday evening. Immediately came to WF and did a search... which confirmed my fears. Apparently because we let the engine (and oil) cool off before replacing the sending unit, the good pressure at idle was just because the oil was a little thicker. Once it warmed up, it flowed more freely and thus the lower pressure.
We are going up to see him next weekend, so I'm planning to put a mechanical gauge on it to see how it looks. I believe it's likely the oil pump because it changed fairly suddenly and I don't think bearings would do that. However, based on the comments I've seen here, it looks like I would be well-advised to change them because we don't know for sure it's the pump, and "while we're in there" ....
My questions for the gurus here:
- first and foremost, I told him he needs to not let it idle with low pressure. If I read things correctly, as long as he keeps it above 13 psi, he should be okay (also watching to make sure it follows the 10 psi/1000 rpm rule of thumb). Is that correct?
- I see there's a high-volume (not high pressure) pump available at a slight premium in price, so is that a good idea?
- I saw mention of "oversize" bearings, assume that's to cover the possibility of excessive wear. Looking online, I only see "undersize" bearings listed (both main and rod). Assuming that's just a terminology difference. Should I use plastigauge first before buying, so I know for sure the correct ones to buy? If so, should I do each bearing separately, or should one be representative? It appears the sets are sold together all one size, so I would need to find the range of existing clearances and find the best match.
- where's the best resource for specs on clearances, torque? I've found sections of the factory service manual available on Scribd but never found a downloadable pdf copy... really like that format best if I can find it.
It's a bit overwhelming thinking about having to do all this on the engine, so I'm hoping I just got a bad sending unit and the mechanical gauge shows good pressure with the engine warm at idle. After my weekend (college and pro teams both lost) I'm betting I won't be that lucky...
If you've read this far, THANKS! Words of wisdom are greatly appreciated!