Well I'm stumped. I got my S70 out of winter storage and took it for a ride to check things out and as soon as it warmed up the oil pressure light came on. I checked the oil and it was full. Did a search the Brickboard and learned all about the "O" ring problem causing low oil pressure with S70's, so I planned to put it away and planned to replace them along with the timing belt. (109,000 miles on the clock) I completed the job and took it for a test drive and and as soon as it warmed up the light came on again. "O Crap"! I can say that I really didn't find any problem with the "O" rings between the pan and block and didn't think I was fixing anything by replacing them and the other seals in the oil pick up and cooler on the rear of the pan. One note I would like to mention about the Oil Sump "O" ring kit. Out of 9 items in the kit only three were useful on my S70. I called FCP and was told that it is the same kit put together by Volvo for all 850 - S/V-70 cars. It needs to be updated in my opinion. There is a pipe in the oil pan between the filter outlet and oil cooler that has a seal on both ends. Both were cracked and hard and I had to replace both with ones from my "O" ring kit. Two large "O" rings on the oil cooler were not also included. There is no place to use the flat gaskets. The whole kit is a rip-off.
Back to my problem. I removed the oil pressure switch and tested it. It is a normally closed switch contact that opens at >10 psi. Conclusion, sensor OK. I replaced it with a pressure gage and was surprised to see the oil pressure at 65 psi with cold engine but as it warmed up it gradually dropped to <10 psi. Increasing RPM did not raise the pressure.
So that is where I am at today. I did some searching to try to find the oil pressure relief but only found it mentioned in a list of things to replace if the oil pressure is too high. It cannot locate it though. Does anyone know where it is?
Someone on the list was recently having the same problem. Was there any resolation?
Of all the low oil pressure problems I found in the search I did not find ONE that indicated that replacing the "O" rings fixed the problem.
A little history on the car.
I got it on Ebay from New Orleans,wanted a southern car. It had 65K miles on it and was not treated very well by the PO. The engine was quite sludgy, indicating few and far between oil changes. I found a lot of sludge in the pan when I removed it. It runs and sounds good except for the noisy valve train which I thought was a result of the low pressure.
Sorry for the long rant, but I'm lost. Going to pull the pan again today to see if I messed up the "O" ring installation.

--
Tom 69-1800S, 72-1800ES, 96-850T,2000-S70 GLT-SE

Hi again Tom.

Dont worry about ranting;its what were all here for,the longer the better!!

Best of luck.

Howard. Isle of Skye.

Hello Tom.
For the sake of completeness try changing the oil filter. it eliminates something simple that can change during a lay up time, especially with a 'sludgy' engine.

I assume that you changed the oil when you did the 'O' rings.

I know for a fact that oil changes with time and conditions,it sometimes forms a jelly-like skin on its surface with standing, what I have seen could easily cause blockages and clogging! In fairness though, if pressure drops severely with engine warm-up;then its usualy wear of some-sort, some-were. Let us all know how you get on.

Best regards.

Howard. Isle of Skye.

Hi Howard,
I have new oil and a new filter. i am going to try to plug the oil filter bypass. (recently discovered)
--
Tom 69-1800S, 72-1800ES, 96-850T,2000-S70 GLT-SE

You mentioned that the lifters are making noise. Does that noise go away after warm up?
If you suspect that there is varnish/sludge in the engine, you might want to investigate running a bottle of Auto Rx to help clean things out. Back in the old "red block" days, it was common practice to add a quart or so of kerosene to the oil to clean out the engine. Some, like my dad, would run the engine for 15-20 minutes with copious amounts of kerosene and then flush out all of the dirt. It appeared to work, considering the amount of junk in the oil bucket. Auto Rx just seems safer :)

Klaus
--
The 164 has a new home, all I am left with are a 95 854T and a 98 V70R :)

The bypass valve is only supposed to work when the filter becomes too clogged to do its job. It "should" not have any effect on the pressure.
When you changed the oil, did you notice if it was thiner than usual? My old 164 had a flooding problem and a lot of gas wound up in the sump, making the oil very thin. At cold temps, the pressure was fine, at warm temps the oil was extremely thin.
With all of the storage, the rings could have leaked down gasoline. I would try a compression test with a cold engine.

Klaus
--
The 164 has a new home, all I am left with are a 95 854T and a 98 V70R :)

re: "...I replaced it with a pressure gage and was surprised to see the oil pressure at 65 psi with cold engine but as it warmed up it gradually dropped to <10 psi. Increasing RPM did not raise the pressure...."

Yes, oil pressure should drop as the oil heats up (because of lowered viscosity), but yours dropped that much?

My old mercedes had oil pressure gauges (real ones, built-in), and cold they'd be up around 30 psi cold and they'd drop to be about 20 psi -- that's with AmsOil 10W-40 (100% synthetic). What oil are you using? Is it a low range, conventional formulation (e.g., 10W-30 dino)?

By the way, I am assuming that the pressures you reported were strictly "idle" pressures. What were your pressures at rpms above idle. FYI, according to Mercedes owners manuals (because Volvo doesn't make any mention of this in their manuals for obvious reasons -- no oil pressure gauge), 5 psi (or 1/3 bar) is the allowable minimum oil pressure at idle; but the gauge must be "pegged" (i.e., be over 45 psi or 3 bar) at any rpm over 1,500.

Good luck.

Ken,
Thanks for the reply.
I am using 10W30 standard "dino" oil. (shell) I understand that the pressure should drop as the temperature increases and the oil gets thinner, but it should never go below 10psi if that is the trip point for the sensor that turns on the light. I have a Volvo spec for oil pressure, 14psi at idle and 43 psi at 3000 RPM. This is from Volvo service information that I have on a CD.
The pressure stated are at idle but it does not increase at higher RPM, at least not enough to turn the light off. (>10 psi)
I think I located the pressure relief valve. It is at the top of the oil filter outlet, screwed into the casting from inside the oil pan. I have an old oil pan for reference. (a man-hole cover knocked a hole in my 850 pan 3 years ago)
I am going to remove the filter and plug it to see what happens.
Will let you know.
Tom
--
Tom 69-1800S, 72-1800ES, 96-850T,2000-S70 GLT-SE

re: "...it does not increase at higher RPM...."

That is serious. At least you've found out before serious engine damage (e.g., running at high rpm and heavy load) -- someone else might not have pursued this as thoroughly.

Best of luck.