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Discussion Starter #1
I've been on this forum reading alot of these threads when zero oil pressure at idle.
I have zero oil pressure at idle when engine is warm, I have done a compression test on all cylinders they have all passed. I have done a radiator compression test this has passed. Changed out my oil sensor in the engine block and I have hooked up a manual gauge for my oil pressure. When I start my jeep up when it is cold, I have good oil pressure and everything sounds right, but as it reaches 210' my oil pressure drops to zero. I have changed my oil 4 times (using 10W30). And I have also checked my CMP and replaced it.
Do I need to replace my oil pump or am I missing a step?

Any info would be greatly appreciated, thanks
 

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Discussion Starter #3
When I start the engine the pressure gauge reads 20psi, as the engine warms up the oil pressure drops. And when the engine reaches 210' the manual pressure gauge reads 0.
 

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I would start with the oil pump. I can't think of any other reason unless the engine is sludged really bad.. I'll wait for others to chine in.
 

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low oil pressure could be either a weak oil pump but most of the time it is because of engine wear..20 pounds on a cold engine is lower than it should be..compression test is only checking the seal on the rings and valves not the wear on the crankshaft bearings,etc..if you want to try to delay tearing into it,try some lucas oil stabilizer..sometimes it helps if it is not too bad
 

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If you bought a mechanical gauge that has 20 as the lowest number with mabye one hash mark before that it wouldn't surprise me that it shows no pressure at idle when warm. If you are idling at around 1000rpm 2 or 3psi will be enough. I don't know where the idiot light comes on for your Jeep, but they are often in the 5-7psi range.
Low oil pressure is often a sign of wear in the crankshaft bearings.
 

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c1skout said:
If you bought a mechanical gauge that has 20 as the lowest number with mabye one hash mark before that it wouldn't surprise me that it shows no pressure at idle when warm. If you are idling at around 1000rpm 2 or 3psi will be enough. I don't know where the idiot light comes on for your Jeep, but they are often in the 5-7psi range.
Low oil pressure is often a sign of wear in the crankshaft bearings.
And/or cam bearings
 

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Stop! Don't buy anything! It's your oil pressure sending unit! This little cylinder thing that like plugs into the engine. Google it. They go out a lot. There's nothing wrong with the jeep. I just replaced mine for the exact reason about three months ago. And don't buy online or from dealer. Cheapest route is to jut go to an auto parts store and tell them what you need. They have them in stock back in the shelves behind the counter. Replacement costed me 25$.
 

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The first thing I would do is to verify with an actual oil pressure gauge that you have a real pressure problem. Then if you do , change the oil and put in 20w-50. If it goes up dramatically then you probably have a worn engine. Meaning bearings, not rings. The thicker oil will raise it. If it still drops to zero very quickly at about the same temp I would suspect the oil pump pressure relief valve or the pump itself is worn out. Hope this helps.
 

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I also get the same exact problem, haven't been able to get a manual gauge on, but also when I'm offroad climbing a hill in a low gear my pressure shoots up on my dash gauge to 80psi! Scares me
 

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Discussion Starter #11
So i took the jeep to a stealership and they said the engine was blown. I do not think thats right they said that they stared the engine and let it run for 10 sec then shut it off and the coolant line was hard and because of that there was exhaust gases in the coolant and there for its a blown engine can't be right? or can it? in my world its time for a 2nd opinion.
 

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WTF? "The coolant line was hard because of the exhaust gases"? Not much of a diagnosis. If the engine was cold and truly built up pressure in the cooling system quicker than the water could have heated and built pressure, I can see suspecting a blown head gasket, a cracked head, or a cracked block. But I would look into it further than that before condemning the engine so quickly. Even if it is a blown head gasket, that in itself is worth fixing unless the engine has been trashed from driving it that way.
More tests and inspections are in order, in my opinion.
 

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Stop! Don't buy anything! It's your oil pressure sending unit! This little cylinder thing that like plugs into the engine. Google it. They go out a lot..
The mechanical oil pressure gauge he added doesn't use the oil pressure sender and it also indicated 0 oil pressure when the engine warmed up which agrees with the OE oil pressure gauge.
 

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Well that don't look good. Somehow I missed that the gauge was subbed for a known mechanical ditto and still read 0...
 

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Pressure in the cooling system is almost always a blown head gasket. Engine compression going into the cooling system.
 

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Had the same problem. Start driving oil pressure normal. 15-20min down the road at stop oil pressure 0, at go oil pressure 20 max. I am skeptical of sending unit or gauge faults because if they show pressure at any time cold/hot/driving/not they are working. So I did a little digging and found this article (definitely check it out, the guy did a good job describing oil in the engine)

http://www.machinerylubrication.com/Read/532/around-around-where-oil-goes-in-your-engine

According to the article clearances on crankshaft bearings get worn and engine can not push oil thru your engine to cylinder head hence the clank of valves when your oil pressure is 0. So I went and bought STP oil treatment and threw it on top of 10W40 and oil pressure improved but not perfectly. Went ahead and bought another one and that did the trick. On start up oil pressure-60, after driving warm up oil pressure-40 and at stop oil pressure-20. It’s definitely a game between summer/winter, oil viscosity (10W40 mean it thickens at 10F and flowing at 40F, so in a summer go higher numbers in the winter go lower), keep it relative to worn engine (please no gear oil ) rather control it with amount of STP (you’ll see that stuff is much thicker than regular oil). You obviously making the engine work harder with thicker stuff but you got to get oil to the top. Meanwhile think of engine rebuild (sorry-you got time though).
 
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