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Old 12-18-2009, 02:34 PM   #1
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oil pressure going from 40 at idle to 60-65

I start my jeep and drive for a few blocks then it raises to 65 and when I floor it up to 80

the oil is new any ideas?

someone said the oil sending unit... does it hurt if I don't replace it immediately

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I got a TJ 99 with 4 wheel drive sittin out back of the jail
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Old 12-18-2009, 03:17 PM   #2
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First, it is normal and necessary that oil pressure rises as the rpms raise. Oil pressure goes up and down in step with engine rpms since the oil pump is engine driven.

Second, what viscosity oil are you running and what temperature conditions are you driving in?

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Old 12-18-2009, 03:21 PM   #3
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↑ x2

Your oil pressure will come down a bit too once the engine is up to full operating temperature. The oil will get hot and thin out a bit and the pressure will drop a bit. It is all normal.
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Old 12-18-2009, 04:02 PM   #4
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I believe its 5w30

so this is normal?

it didnt do it when it was warm out... now its colder and it does it a lot

it gets up to 80 sometimes

driving temp is about 35-40 degrees
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I got a TJ 99 with 4 wheel drive sittin out back of the jail
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Old 12-18-2009, 04:58 PM   #5
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The colder it is the thicker it gets and makes pressure go up, hence the phrase thicker than molasses in January.

However... 80psi is a little too much and the oil pressure relief valve should not allow it to get above 75psi I wouldn't worry about it too much. BUT till the engine is fully warm I would keep the rpms down a bit . When the engine gets hot the oil will thin out and the pressure will drop. It it ever gets up to 90 psi or more I would start to look into it and see what's going on. 5W-30 is fine. It is a thinner oil and is better for your situation.
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Old 12-18-2009, 11:17 PM   #6
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Remember too - the indication on the dash is just an indication, not real. It's an "interpreted value" by the computer. If you really are concerned, plug a mechanical oil pressure gauge in. Bet you'll find it's in the normal range, not 80lbs.

Mechanical oil pressure gauges are cheap. You don't need to install it permanently, just temporary for the test.
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Old 12-24-2009, 12:38 AM   #7
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*Check Gauges*

So, is it typical for the pressure to drop at idle and the *Check Gauges* light to come on? It drops, and comes back up to about 40 almost instantly. I'm looking at a 97 4.0 5spd that is doing just that. Otherwise, it's pretty sweet.
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Old 12-24-2009, 12:42 AM   #8
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Quote:
Originally Posted by New2Jeep View Post
So, is it typical for the pressure to drop at idle and the *Check Gauges* light to come on? It drops, and comes back up to about 40 almost instantly. I'm looking at a 97 4.0 5spd that is doing just that. Otherwise, it's pretty sweet.
A check gauges light period isn't normal... that sounds like a bad sending unit causing that. If it is indeed a bad sending unit, you might be able to talk them way down in price for a simple fix. If it's something major...you could end up having a serious repair to do very soon.
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Old 12-24-2009, 12:51 AM   #9
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What would be the best way to find out if it's a sending unit or not? I could probably talk them into letting me take it to a local shop for inspection. Or would I be wasting my time doing that too?
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Old 12-24-2009, 03:03 AM   #10
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mine is still doing this but when its been driven for a while it stops... yet it didnt do it when it was warm out

im going to try to replace all the gauges with real gauges(soon as a find what to do about the odometer and check lights
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I got a TJ 99 with 4 wheel drive sittin out back of the jail
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Old 12-24-2009, 09:11 AM   #11
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Sending Unit

Quote:
Originally Posted by jdub2k5 View Post
mine is still doing this but when its been driven for a while it stops... yet it didnt do it when it was warm out

im going to try to replace all the gauges with real gauges(soon as a find what to do about the odometer and check lights

I talked to my local dealership, and they said they've had quite a few sending units to replace on the TJ. I don't know... The seller is going to replace the sending unit, so hopefully that's the fix! I think I'm going to be a Jeep owner soon!
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Old 12-24-2009, 12:22 PM   #12
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Quote:
Originally Posted by jdub2k5 View Post
mine is still doing this but when its been driven for a while it stops... yet it didnt do it when it was warm out

im going to try to replace all the gauges with real gauges(soon as a find what to do about the odometer and check lights
First, as opposed to newer TJs where their gauges have been reprogrammed to not precisely show what's really going on that scares some people who don't know what the gauge indications really mean, your '98 TJ's gauges do indeed read accurately.

Again, your oil pressure gauge is SUPPOSED to indicate higher pressure like it is doing as you accelerate... especially if you accelerate hard. Then the pressure will drop back down once the engine rpms go back down.

Pressure can read higher than what you may be used to for reasons like a cold engine and cold oil. The colder things are, the higher the oil pressure will be since cold oil is harder to pump.

So ignore the advice that the TJ's gauges are inaccurate, that is only true for newer TJs that were reprogrammed so as to not unnecessarily alarm the clueless. That doesn't apply to older TJs like you and I have.
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Old 12-24-2009, 01:50 PM   #13
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My 04 only has a L-H indicator on the dash gauge. The sending unit failed a few months ago and dropped to zero, since there was no tapping or knocking and I was just 1/2 block away from home I ran it home and replaced the sending unit. Everything is back to normal. My yj went 200k on the original. I guess if they make everything last forever the dealers/auto parts stores will go broke.

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