Low oil pressure!!!

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79sunrunner

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Hi, a friend in need for advice!
I've got a Jaguar XJ8 with the 4L V8 engine. I currently run 5w/30 synthetic oil with the AutoZone label (I know some brand name sticklers would be infuriated right now) but the oil does carry the API symbol and acclaims GF5 standards. Anyway, the oil pressure is on for a second or 2 during startup: like anyother car with 98,000 miles like mine. But as I drive the car 1.5 mile down the road there is a stop sign and at that stop, very rarely the low pressure light would come on. This terrifies me, I always shut the car off and recheck the oil level (even though I do it once a week) and the level is always spot on. What would you guys consider? different oil? Some special tune-up for these Jag engines? I'm on a shoe string budget as well. Thanks for reading
 
Are you slamming on the brakes when you come to the stop sign which may slosh away from the oil pump pickup for a brief moment?
 
I usually coast from 55mph to around 30mph before I gently get on the brakes, so that isn't the cause. But when the oil light does come on, I feel a strange sinkingness to the brake peddle and sometimes the engine fluctuates
 
Any Synthetic should be pretty good.

Sounds like two things.

1. Sounds like the Anti Drain Back Valve on your Oil Filter isn't doing it's job. You might want to upgrade to something with a silicone ADBV.
The oil is draining back over night and when you start the engine it takes a second for oil pressure to return to what it should be.
It's actually a really common thing.

That being said.
2. You may have a bunch of build up on the oil pressure sender (if it was previously owned who knows what was run in it). It sounds like it may be an electrical issue. Could be either or both.
You might want to check any sensors, and do more research on the issues on a Jag specific forum.

Have you had the car since new?
If the oil pressure sender is heavily varnished, or sludged, then that could cause false readings.
 
As far as previous owners, the car was beaten to death for the first 10 years of its life while spending an additional 4 years siting in a warehouse. The previous owner was 19 (my age) and owned a mint condition XJR and wanted a normal Jag for work. I often wondering why he didn't keep it long before he sold it to me? Honestly I bought this car only to own as a final (fun car) before I move out and go on my own. I've look into the sender tomorrow and see if there is any contamination on it and check the seals. As for oil filters, I used to run the Jaguar OEM ones, but at $18 a filter, I wanted something more reasonable for my 4500 OCI. I'm now running the standard Bosch black filters, I thought they had anti drain back valves in them?
 
Bosch makes a good filter.
Yes, it has a silicone Anti-Drain Back Valve.
So you should be good there.

Your short intervals on Synthetic are a good thing since it has been "beat to death" as you say.
Even the cheap synthetic should be cleaning some stuff up, if there is anything to clean up.

My bet is that this is from the previous owners neglect.

If you have the ability to do so I'd dissect the Bosch Oil Filter after this 4,500 mile OCI. It will give you a better idea of what you are dealing with.

If you find that you have a mess to clean up I highly recommend Pennzoil Platinum. It has a good following on these forums and lots of people have used it to help clean up their engines.
 
Thanks for the advice. I figured the engine would have some sediment lying around so that why I went for the lower cost oils and filter. If it were new, I'd be running anything that meets the manufacturers taste. Last time I looked, the PP looked well priced for its performance and customer satisfaction, so I will take them on this weekend (4500 miles is up)
 
is 5w30 the correct weight for that engine? sometimes different oil weights can affect oil pressure.

also if the idle is dipping low on a stop that could trigger the light. if the engine is dipping below recommended idle it will have lower oil pressure.

check the Idle air control valve and clean the throttle body if it is idle related
 
I would suggest running a thick 30 weight on the next change, possibly a diesel-spec 10w-30 like Rotella T5. The strong add pack will help clean the engine, plus the thicker weight might quell that pressure light. Certainly can't hurt to try.
 
yes the recommended weight is 5w/30 and the idle is a tad high (600 rpm when the original is 550) I thought about putting in 0/40 to see if that would help, but I'll try cleaning the sender unit first since I don't favor playing with oil grades. We'll see what happens
 
Originally Posted By: 79sunrunner
I usually coast from 55mph to around 30mph before I gently get on the brakes, so that isn't the cause. But when the oil light does come on, I feel a strange sinkingness to the brake peddle and sometimes the engine fluctuates


Is the engine nearly stalling, which causes a flash of the OP light ?
 
Originally Posted By: mechtech2
When cold, the oil is thick. Thicker oil is not the solution, then.
I think it's the sensor, connection, or wiring.


Exactly. NEVER trust an oil pressure sender. The readings can be totally wacko in either direction. ALWAYS check with a real mechanical gauge to verify the readings first.
 
Originally Posted By: simple_gifts
I would verify the sending unit is not malfunctioning.

I would start with the sending unit also. And/or, install a mechanical gauge to see what is actually happening.
 
Originally Posted By: KrisZ
That is why it is good to stretch the engines RPM band every once in a while instead of putting around for eight years. All sorts of carbon deposits could've been loosened all at once and cause trouble.


Yeah that works, loosen the carbon and loose oil pressure, sorry but that's a crock...

If it's a low level indicator(NOT pressure), possibly the sensor in the oil pan has a issue, could have been damaged from the high RPM splashing of the oil... If it's a low oil pressure, then you better be finding out what the issue is ASAP...
 
Originally Posted By: TFB1
Originally Posted By: KrisZ
That is why it is good to stretch the engines RPM band every once in a while instead of putting around for eight years. All sorts of carbon deposits could've been loosened all at once and cause trouble.


Yeah that works, loosen the carbon and loose oil pressure, sorry but that's a crock...

If it's a low level indicator(NOT pressure), possibly the sensor in the oil pan has a issue, could have been damaged from the high RPM splashing of the oil... If it's a low oil pressure, then you better be finding out what the issue is ASAP...


Oh, so high rpm cannot loosen carbon deposits in the engine, but can damage sensors? Your logic is irrefutable.
smirk.gif
 
Last edited:
Originally Posted By: KrisZ
Originally Posted By: TFB1
Originally Posted By: KrisZ
That is why it is good to stretch the engines RPM band every once in a while instead of putting around for eight years. All sorts of carbon deposits could've been loosened all at once and cause trouble.


Yeah that works, loosen the carbon and loose oil pressure, sorry but that's a crock...

If it's a low level indicator(NOT pressure), possibly the sensor in the oil pan has a issue, could have been damaged from the high RPM splashing of the oil... If it's a low oil pressure, then you better be finding out what the issue is ASAP...


Oh, so high rpm cannot loosen carbon deposits in the engine, but can damage sensors? Your logic is irrefutable.
smirk.gif



And I thank You for your acknowledgment...

Sure a good high speed run can loose carbon, I never said it didn't, but it's NOT going to effect oil pressure... And yes the oil LEVEL sensor can be damaged by the oil whipping around in the pan, they are only a small float assembly inside a small cage... Probably would not effect a new one, but I've seen older ones that were brittle and had cracked floats that allow the low level light to remain on...
 
Check the sending unit and its connection. No one has mentioned this, but the next concern would be the oil pickup scree of which I would drain a qt. oil and try a qt of MMO for a cleaning cycle.
 
Last edited:
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