Fluctuating Oil Pressure

[BarryHarwood]

Hi there, I have a 4JG2 engine and since last week when I changed the oil I have noticed the oil pressure gauge moving around quite a bit.
At start up it sits around 6 bar, which it has always done and as it warms drops to 4-5 bar, but now it sometimes drops as low as 2 bar regardless of loading, or rpm etc. The oil is rated for diesel engines 15w40 which i believe is correct. I have noticed a very slight knock from the engine when under load but doesn't sound major. The oil light doesn't come on when the pressure is reading low and when the needle does move, it is slow and deliberate (so i don't think its an electrical short), Has anyone else had an issue like this?

Cheers
Barry

[geeves]

The guage is in kg/cm2 but this is as close to the same as a bar that for oil pressure it doesnt matter.
Different oils have different characteristics despite being supposedly the same. Not so sure how the 4jg2 behaves but my 4jb1 when cold gives 4 kg/cm2 and drops at idle when warm to between 1 and 2 The oil light comes on at about 1/3 kg/cm2. When I was useing Repco oil when it had done about 4k and was hot it would drop off the scale Repco oil also burnt a little bit. When I used Dello gold it was the same old and new and hot would still be sitting at 2 hot idle. Now useing Valvolene diesel extra and when new it will read 2 hot idle but this drops to arounf 1.5 once the oil gets old. Why did I change from Dello Because it caused the engine to leak. Changed to valvolene and the leaks stopped

[wbski007]

still could be just the gauge or sender going bad, I'd get a good machanical gauge to replace the factory one, to be on the safe side

[BarryHarwood]

Cheers guys,
Funny you should mention Repco oil Geeves, that's what I put in it this time. I usually use Valvolene so may just cut my losses and treat this as a flush and see how she goes on the Valvolene again.

Thanks again
Barry

[geeves]

Im not allowed to publish my opinion of the stuff on a family friendly forum

[wbski007]

I don't think we have repco here in the states and by what you guys are saying I'm glad we don't, Valvoline has always been a good oil, its been around for ever.

[geeves]

Repco is a marketing company. Walmart sells oil but would you buy walmart branded oil. Sometimes its ok but each time the contract to make it comes up the formulae may change and as its made to a cost you can guarantee its not always premium ingrediants

[wbski007]

OH, its that Walmart crap, you guys got Wally worlds over there too HUH. geeze their speading all over, now that you mention it that is the name they use. I wouldn't use that stuff in my lawnmower, God only knows who making it, I think it changes every week.

[geeves]

Closest we have to wallmart is Kmart which is a chinese style Aussi copy. I only picked on them as an example as they are a large chain store that sells everything

[sailfish]

Hi Guys,
I am new to this web site, I have been looking around and found heaps of very useful information and lots of people that are keen to help others out, which is great. When I found this string it was of great interest to me as I am currently trying to sort out a similar problem to the one Barry has come across.

I have a 1996 Isuzu MU 3.1 TD, I have owned the car for about 4 years now and the oil pressure has always been just under 6kg/cm2 on start-up and would drop to around 4.5-5 kg/cm2 once the engine has warmed up and is sitting at idle. When driving the oil pressure is always just under 6 kg/cm2.

A couple of weeks ago I pulled up at a set of lights and watched the oil pressure gauge fall down to around 2kg/cm2. Immediately I listened for any sounds coming from the engine however everything sounded the same as normal. As I pulled away from the lights the oil pressure rose back up to where it would normally sit just under the 6kg/cm2 mark on the gauge.

So what I appear to have now is a running / accelerating oil pressure of just under 6kg/cm2 (around 5 – 5.5kg/cm2), a warm idle oil pressure of about 2kg/cm2 and a cold idle of just under 6kg/cm2. A mate has put an oil pressure gauge on the engine and tested it for me and confirmed that this is the correct reading.

My question now is do these numbers sound correct for this engine? I understand that the gauge may have been faulty from the word go and is now giving a true reading. But I have always been told that it is often not the oil pressure that your engine runs at that causes a problem, more so a fluctuation in that “normal” oil pressure for the particular engine. So I am kind of stuck here, if these numbers sound right for the engine the gauge was giving false readings, but if the numbers are wrong and the oil pump or something similar is the problem I could damage the engine if I keep driving it.

So if anyone has any thoughts on this I would really appreciate your input.

Cheers
Greg.

[geeves]

All those figures sound normal enough. To convert back to PSI multiply by 14 so you still have close to 30psi at hot idle. Different brands of oil can cause fluctuations like this with full synthetics hardly changing hot or cold but some mineral oils being quite variable. Also age of oil and the amount of contamination plays a big part. Do change your oil every 5000km and your filter every 10000 (some people change filter every 5000)
One other thing that might of changed is that if the previous owner wasnt as finicky with oil changes the bypass may of been blocked but this has now cleared with clean oil.

[sailfish]

Thanks Geeves,
Some interesting info there, I didn't know that was the conversion to psi. I make sure that I change both the oil and filter every 5000km's. I was hoping those figures sounded ok, as you can imagine when I noticed such a difference in oil pressure I was a bit shocked and not really sure if I should be still driving the car or not..... So it would appear that the gauge was previously not functioning correctly.

[slomo]

I have had my Bighorn for over 8month now and when cold the reading is about 4. When the truck warms up it sits at around 1 and a half and 2 when driving at about 8okm/h but when idle it you can watch it drop down to what I can see 0. The oil light comes on the dash and my oil level is acceptable.
If my pressure/level was really that bad i'm sure my truck would be dead or really noisy wouldn't it?
It has been doing this since the day I owned it, I have doen a oil and filter change with Valv Diesle extra and it seemed to make it a little better

What would be the best approach to tackle this?

[turnturn]

Try fitting a new oil pressure sender unit or/and fit a manual oil pressure gauge.

[geeves]

What mileage?
It might be a gauge but it could be worn bearings or a stuck bypass or a worn pump. If the pressure comes up above idle it shouldnt be doing much harm but I would still want to know if its a gauge or something serious.
Its common on very high mileage engines and engines that have not been well maintained to have low oil pressure and these engines are in the autumn of there lives.

[slomo]

Cool thanks guys
Speedo says about 188K but carjam says it has decreased so i'd say about 250K

[geeves]

People dont wind back speedos in NZ except maybe at point of entry. More likely the speedos been replaced. Take this as 250 +- 250 Send me a pm with the rego and Ill look at carjam and try and second guess it.

[Captcol]

some people with diesels do disconnect the speedos for periods of time to avoid road taxes though

[geeves]

true but both me and this club believe people should pay there taxes. (we wont dob anyone in tho)
Actually any comments on evading any legal fee should not be posted in any public forum. Mr taxman might be reading and if they ever demanded by warrant any members details we would have to comply

[slomo]

People dont wind back speedos in NZ except maybe at point of entry. More likely the speedos been replaced. Take this as 250 +- 250 Send me a pm with the rego and Ill look at carjam and try and second guess it.

PM sent