Hello, greetings from Australia. I have an 850 SE 2.4l 10 valve engine. I am experiencing various problems with this car. Sadly I just can't afford to sell it at this condition.
Here are the problems.
1. I noticed few days ago that my rpm goes up and down while the transmission was in N. (went to 2 and went back to 1 and quickly went back to 2 and then back to 1, several times) Also there is time when the rpm stuck on 2. I mean when I drove the car (transmission on D) then I stoped and put the transmission back to N, the rpm goes up to 2 and stayed at 2 but when I turned off the engine and restarted it, it went just like normal. This happened only few times for 2 days (started 23/12/09), but until today, it does not seem to happen again...strange...what may cause this? Idle control valve problem? I read about this too..

2. Then in that same day 23/12/09, temp gauge went up to almost red line...I quickly pulled over and turned off the car. Checked coolant and everything...looked normal (coolant was still between low and max). Turned on the engine again after with A/C off (we are in summer here in Aust), temp gauge went to the middle for like 15 minute driving then slowly went up again. Lucky I was close to home...so after 5 minutes wait, temp went down and I drove in my garage. My regular volvo workshop was closed at that time (was late) and they are having christmas break till first week of january so I couldn't get help. Then from various reading online, I found out that maybe the thermostat is not working properly. My neighbour also suggested that. (he has some automotive know hows) and he does not believe my water pump or radiator are the problems but he advised me to give my radiator a flush. So I did. I flushed the radiator with the radiator cleaner chemical. But short story..it didnt work...the engine still overheat. Then on the 26, I called volvo part dealer and ordered a thermostat plus sensor (cost me AU120 in total). Replaced the thermostat and I was dancing happily as It fixed the problem.

3. Then my instinct told me to check the oil from the dipstick. I must admit I rarely check the engine oil level as I would never have that in my mind. (work as early as 4 am and finish at 6 pm, pretty much exhausted)I almost jumped to the roof as I found out that the dipstick showed me virtually NO oil, not even on the lowest point. I was puzzled as i never notice any leak and I always take the car to service for oil change. (ok the last service was 2 months late as I forgot about it but I don't use the car much only 7 minutes to work and 7 minutes back and very occasional fishing trip 4 hours drive like maybe once or twice in a year) then I quickly went to get a 5 ltr jug of 15w40 oil (shell) and I filled up the oil. Took about 3 litre of oil and I thought well, its not so bad...i still had at least 2 litre before.

After that, everything seemed to be ok as the car wasn't showing any abnormal behaviors, until one day I checked the dipstick and it was puffing smoke...not thick though. And I said to myself...hangon...this is not normal. I checked again online and asked the workshop. Both suggested me that I have clogged pcv system. And to replace and service everything, it will cost me $500 not including parts. Oh my... But I have a hunch...could it be caused by mixing different oil in my car's engine? The oil I bought to topup is shell 15w40 for general use. I choose 15w40 because it can be very very hot here in Victoria in summer (last summer the temp went upto 44 degree celcius).

4. I also notice a little squeaking sound on the left side of the engine. It sounds like timing belt.

Other than this, the engine starts quick, not limping in anyway. It still has normal feel of acceleration/power.

Please help me of what I should do first as I don't really have the money to replace everything together at once. This christmas season has drained my pocket.

I know it is possible to do these maintenance myself but I still need the tools. (I do have tools but it may not be sufficient for these kind of jobs). But if buying the tools required beats the labor cost of volvo workshop...I would gladly do this alone no matter how long will it take (I may not be able to do the timing belt...this has to be properly installed, cant afford for error). I know there's haynes manual for 850s and I have read some online DIY steps by steps about maintenance and parts replacement. Please let me know what tools would I need for these kind of maintenance...and how much roughly they cost?

Sorry for the long post but I just don't know what to do. To let the volvo workshop do the job may seem easy but I can't imagine how much they charge for all of these jobs...not including parts cost. It would cost me 2000 bux at least.

Thanks again, all comments are very much appreciated

 

4: If the timing belt has not been replace as recommended at milage recomendations, have it replaced with the pulley's etc.

3. Check oil at every fill up until you figure out where the oil is going. Maybe you have a plugged PCV system. When the car is warm, does smoke come out the oil dip stick when you pull it out a little with the car running?

2. Probably the thermostat. Very low price part and easy to change.

1. Could be idle control valve or some sort of vacuum leak.

 

Your PCV is probably plugged... as for the oil, find out what Volvo recommends, and stick with that... 15W40 is way too thick, though, even for those temps. I know that here in the states, Volvo recommends 10W30 for most temps, including very high. You can safely use 10W40 according to the manual, but again, that's going by US- spec cars, and they didn't sell the 10- valve engines here, all US 850s had 20- valve engines.

As for the overheating, it's often the thermostat.

Timing belts shouldn't squeak... unless the idler or tensioner pulley is going... it's probably the serpentine belt that's making the noise.

 

Thanks for the reply. I have done the thermostat (replace that and the sensor), it fixed the overheating.

I also think pcv needs servicing...I have done some research about this...its possible to do it myself no matter how long will it take...i will take my time =D

Now the "auto" reving happened again this afternoon. This time it does not stop although I restarted the engine off and on. I know it has something to do with idle control valve or vacuum leak somewhere. Anyway to test this?

Yeah I notice the thickness in the engine oil...probably should get the 10w40 or 5 w40 even...but its only for temporary anyway cus when I do the pcv I am planning to change the whole oil again. By the way...would anyone tell me what are the effects of thick/thin oil to the engine?

Thank God someone does not think it is timing belt noise...what is serpentine belt? Is that the air cond belt? or fan belt?

Which one is the most important I need to do first? Thank you very much