Drop in oil pressure

[Land-Rover SI]

The last 2 times i was out driving for more then 30 - 45 minutes i have noticed something strange:

It goes like this:

After have been running really smooth with normal oilpreasure and temperature on engine for about 30 minutes i get a strange reaction from the engine when it has to work a little harder in a hill or so...

Suddenly the oilpreasure drops some and the engine sounds a little more harder and the power goes down just a little bit. If i then ease off the speed or stop and wait a couple of minutes the engine sounds normal again and the preasure is up to normal range.

I checked the oilstick at once the first time it happend and there is no oil missing.

I have reasently changed oilfilter and oil. I now use a fully synthetic oil 5W-40 and it has only been in the engine for the last 200 km.

What is happening?

[asavage]

Is your oil pressure gauge a mechanical unit, or does it use an electrical sensor?

I am not coming up with any good guesses.

[kassim503]

Ill take a shot, I guess it could have these symptoms. It might be the oil pickup a little loose, not too loose but enough for it to move a little at higher rpms and suck in a little air. Or if you have a electric gauge its just a bad connection, dont explain the noise though.

[Land-Rover SI]

I posted the same at the Norwegian L-R forum and there they said that it could be that the synthetic oil is to thinn and cleans the engine a little to hard so that the coal and sediments gets cleaned to much and then the play thats in a old motor gets to loose.

They recommended me to switch back to good mineral based oil.

What do you say to this theory

[asavage]

I say no.

For one thing, synthetic oil does NOT "clean" existing deposits, and anyone who claims it does does not know about which he speaks.

Secondly, synthetic oil is not very much "thinner" than mineral oil. 5W40 is fine for this engine, if it is a true synthetic.

Thirdly, synthetic lubricants have superiour lubricating, dispersal, and acid-quenching properties as compared with mineral-based oils.

And lastly, how does that theory explain the variable power output?

=================

Really stretching here, but one thing that would yield lower oil pressure AND a reduction in power would be some kind of restriction between the output of the oil pump and the galley where the OP sender resides. Perhaps I'd make certain that you are using the correct oil filter. There are three bypass/relief valves in the oil circulation system (see page LC-11), but if one or more failed shut at some time, it's possible that the oil pump could be overloaded, and oil flow reduced downstream.

Again, I'm really making this all up. I'm hoping someone comes up with a better idea.

And, you could certainly drain your synthetic oil out and install conventional mineral-based oil as a test. I would definitely keep/re-use the synthetic oil. I've been known to be wrong before.