'95 Jeep Grand Cherokee - Flucuating Oil Pressure Gauge

Reply Sat 31 May, 2014 10:56 pm
Definitely a candidate in the "better late than never" category of problem - I finally took the steps today to successfully resolve a persistent problem with my '95 Jeep Grand Cherokee, that I first noted more than 10 years ago (yikes!). And in complete candor, I could have sworn I had posted this problem years ago, for the collective audience to review (and admire) - but apparently I was mistaken about that . . . . Regardless, while there's no problem to solve here, I just thought others might benefit from reading about my problem, and the eventual solution (in case someone might want to narrow the intervening timeframe).

To my shame and discredit, more than ten years ago, I noted some odd fluctuation on the oil pressure gauge of my Jeep Grand Cherokee while under power and driving. The oil pressure gauge mostly reflected a high pressure reading, with the gauge needle pegged out at the maximum reading. Only occasionally while stopped and idling, did the gauge needle ever drop off the maximum reading.

Being mindful of the potentially catastrophic engine damage that could result with a too low oil pressure situation, I did run through a set of standard diagnostic steps to ensure that oil was circulating and that there was sufficient oil in the system - and everything checked out. And to be perfectly honest, any of my "shade tree mechanical background", had me unprepared to even know what to worry about, with a too high oil pressure problem. Regardless, my suspicion immediately went to the likelihood of a problem with either the gauge itself or the engine oil pressure sensor switch. Unable to pinpoint that myself, and with no other outwardly observable symptoms or other untoward engine or performance problems - I opted to just live with the problem for the last ten years . . . and the Jeep has performed nearly without problems during that intervening period. Oh yeah, the radio stopped working a couple of years back, but I was pretty sure that was unrelated to any issues associated with oil pressure fluctuations.

Here recently, I've begun to entertain the idea of selling my Jeep Grand Cherokee, which is in remarkably good condition overall, with everything working on it (except that darn radio and now the electric antenna . . .). On the assumption that any potential buyer might understandably be "unnerved" by the sight of the fluctuating oil pressure gauge - I decided to go "all-in" and attempt to repair this +10 year old problem.

Recognizing that there was probably not a lot of likelihood of a problem with the oil pressure gauge, and recognizing that in the replacement order of difficulty - that tearing out the dashboard to get to and replace gauge rated pretty "High", I opted to target the engine oil pressure sensor switch. I ordered a new switch from my local big box auto parts place (and got a 15 percent discount for ordering on-line for the first time) which came to a total of $29.75.

I'll concede that I've been a little uncertain of where the oil pressure sensor switch is located on my 4.0L engine, but with new switch in hand for visual comparison, a quick inspection showed that it was located directly above the oil filter inlet (who knew . . . ?). Armed with a crescent wrench, in less than 10 minutes, I had the old switch unhooked, unscrewed and the new switch in and reconnected.
A quick test of firing up the engine showed that the gauge was now reflecting a constant - and likely correct oil pressure reading. My only caution is that you will not want to over-tighten the sensor, as a light snugness, seems to be sufficient to seat the unit, and prevent any oil leakage.

Just for fun, I ran this through a repair estimator for the local area to see what my 10 minute repair (or 10 year repair . . . depending on when the clock starting running exactly), plus my $30 part would have cost me.
Looks like I came out ahead of the game again. Next time I just need to do something a little sooner than 10 years . . .
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Reply Mon 7 Jul, 2014 07:06 pm
Here's a "smart tip" follow-up, to the fix to the oil pressure sensor switch replacement. About a week after replacing the oil pressure unit, I began to notice a little oil leakage from the vehicle - where up until now, there had been none.

Correlating the replacement of the oil pressure sensor switch, with the sudden appearance of oil - when the sensor is intended to measure the pressure of oil in the engine, wasn't a difficult exercises of "connecting the dots".

On the assumption that I was getting a tiny bit of oil leakage past the threads on the sensor switch, I removed the sensor, and added two wraps of Teflon tape around the threads on the sensor - and reinstalled it.

No more oil leakage.
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