I read a closed post about the use of Seafoam, thought I'd add my experience. I put in half a bottle in my 96 850T with 225,000, drove about 175 miles before changing the oil. I drive like a little old lady, and I took extra care not to rev the engine during this time. I have driven about 3000 miles since, and have not had any issues pop up. I also added a bottle of Techron to the gas tank (with 11 gal. of 87). I was hoping one of these snake oils would cure a tick I have had in the engine since I bought it 60,000 miles ago. My compression went up 12% (an average of 88 increased to 99), so I guess the Techron did some good. I beleive that Auto RX will do the same thing as Seafoam, at least according to one of the local indy shops I use.
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'96 855 Wagon, 200k (and formerly 97 850, 120k)

It's not the gas. I've had my 94 turbo since 01 with 107k and now it has 255k. I've ALWAYS used regular gas with absolutely no(not noticable) effect on performance. Occasionally, I put 100 octane and nothing changes ie: mpg, running cooler, etc. I still get 28mpg hwy doing 72mph. The only thing I can say about the oil is that, when I use regular oil 10/30w it ticks less.

The tick is more than likely the oil pick up tube o-ring. Get the kit
and replace it. Should work.

Actually driving the car 'like an old lady' is not good. You need to do the opposite. Something called 'Italian tune up'...
Drive it at high RPMs for few minutes. That will help push the crap through. I've done it successfully many times.

Sadly it does not always work. I bought a 64,000 miles 850 that was babiesd., probably never revved over 3000.

Full tune up, oil change and all, PCV replacement, all hoses, etc. All was well for 20,000 miles and then I did an Italian tune up (never hit the rev limiter though), and now I burn a quart of oil every 750 miles. Busted a ring as best as I can tell. I was very surprised on an engine with this few miles.

'Italian tune up' wouldn't cause that. This engine was already abused. Probably infrequent oil changes, air filters, etc...

Use 91 octane or the closest available. The car will run better.

I hadn't thought of that. I have had 850s since 2000, and I always use 87 (or 89 if it isn;t available), never had any issues. I just thought that was a scam Volvo had with Big Oil to get us to buy the more expensive dinosaur juice.
thx.
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'96 855 Wagon, 200k (and formerly 97 850, 120k)

I used Reg Unleaded in my '95 850T for 50,000 miles, and it always ran great. No performance issues at all (other than marginal mpg), and I drive in a spirited way a portion of the time.

The computer will compensate for a tendency to knock. I never heard any pinging at full acceleration. I guess you may build up more junk in the engine.

Who knows, maybe the new owner is having problems.

It's pretty tough to make a modern engine with knock sensors and computer controls actually create a pinging noise that you can hear. The knock sensors notice it long before your ears could and the computer corrects the fuel...
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1998 V70 AWD->FWD Turbo 200k+

You need a better compression tester. A turbo should have a minimum of 155psi to a perfect 187psi, and all 5 within 10psi of each other. Less than 100psi would result in no burning of fuel.

You should also be using a minimum of 89 octane, preferably 91-91 octane. If you drive like a little old lady, stop doing that! The turbo engine NEEDS to spin rapidly, over 2K to keep the valves clean.

If you are not using 5/10W30 synthetic with a Mann or OEM filter, then do so at your next oil change.

Don't rely on aftermarket engine cleaners to keep your engine occasionally clean, treat it nicely every day with good oil, gas, and spirited driving.

Klaus
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Proud owner of a 220S. If I had more room, I would have more Volvos.