me again, in an effort to solve my rough idle problem im replacing the temp sensor and thermostat. but there are 2 thermostats 87 and 92 degree. does it matter which one i purchase? i did recheck the codes on module a #2 and a code 123 showed up. i cleared the codes restarted for a while and the code never came back, so maybe something is up with the coolant temp sensor. would a faulty temp sensor be a cause for strange idle when first started. one other thing i noticed is when it gets warm the gauge is pointing at 3 its used to be at like 4 and it warms up way faster than usual. thanks

 

cleaned maf, issue solved for now

 

I'd still replace the coolant temperature sensor at the very least.......If you replace the thermostat, the hex head bolts on the thermostat housing cover are easy to round out. Do yourself a favor...when you get them off, go down to your local hardware store and replace them with hex head bolts.

 

The thermostats start to open at (180F) 87deg C for the turbo and (186F) 90deg C for the NA. Depending on which you have it's best to stay with the correct one for your vehicle.

Faulty temp sensor will send faulty information to the computer and the computer will send the wrong amount of fuel to the engine. May go rich or lean depending on which way the sensor is off. Yes it can affect your starting, idling and fuel economy going down the road.

That 3 O'clock position seems to be the normal fully warm operating position from most people I've seen talk about heating issues. If yours is sitting at 4 O'clock it might be a bad thermostat that is opening too much and not allowing the engine to get to it's proper operating temp.

You might want to consider doing the thermostat just in case it's starting to go out.

 

Real good idea to replace the torx bolts with hex heads. And a little anti-seize wouldn't hurt either.

 

i ordered the corect part thermostat and sensor. the thermostat looked ok but replacing both anyway as recommended. hope it helps

 

Are you kidding One is for a turbo.

There are two, one for a turbo and one for the NA (natural aspirated and or non-turbo). Your signature says your 850 is a NA. You get the one for an NA, the one that starts to open at 186deg F.

In the real world I doubt that 6 degrees either way is going to make much of a difference but if you have a choice I'd go for the one with the stock temp.

 

90 c is what ipd is selling for both turbo and non turbo, so i bought it should be fine

 

kiss- you mentioned a bad sensor will send incorrect info to the computer. That makes sense, but the places I've been talking to (temp gauge not at 3:00, maybe 3:30, 3:45, and no codes) tell me if the sensor was bad it would shoot a fault code to the computer. So I havent replaced the sensor. Have replaced the thermostat. Still trying to get to the bottom of the non 3:00 guage. Hot coolant measured 192 with infra red gun. Oh, also my radiator fan has never once turned on. tryin to sort that out too. Add it to the list... Dave

 

If you read operating temp with a thermometer but the computer still says it is low then the temp sensor has a problem. It does not have to trip a trouble code to be bad. In fact it will only trip a DTC if it sends a signal that is out of operating range.

 

OEM t stat and sensor! you know it'll be the right one! Too warm or too cold = rich idle + bad MPG.

 

What he said !!

Think of it this way. Your car doesn't know if it's in Alaska -20 degrees, Rhode Island +41 (presently) or Death Valley +102 degrees.

So if the computer "sees" a temperature from -30 to +120 the computer thinks that is the temperature and sends in that amount of gas to start up your 850 !! If you're in death valley and your sensor tells the computer -20 you'll flood the thing out before you ever get it to even pop. If you're in Alaska and that same sensor tells the computer it's +100 degrees it's going to spin and spin and spin until you run out of battery and it still most likely will be too lean to start up. In both cases you will not get a trouble code to set because the temps the sensor is sending are within the operational parameters of what they could be.
That is why you need to know what the actual temperature or physical temperature of the coolant or engine is and compare that to the electrical temperature reading you get from a code reader of what the sensor is telling the computer.
That is where it gets a little tricky and you have to be smarter than the car !!

 

Thats what I needed to know, weather a bad sensor would trip a code or not. So to be safe I'm just going to replace it. Now I've seen a couple different kinds with prices ranging from 18 to 60 bucks. has anyone had a bad experience with the less expensive ones. I've also noticed after reading around that many have had to go through multiple new sensors before they got a good one.

 

I was in a pinch (didn't have time to order OEM) so I got one from NAPA that was $50. I forget the brand, but it was something I had heard of before. Been working fine for two months.

 

Do these sensors go bad? Quickly?

I just replaced one two months ago in a 1998 S70 that wouldn't start.

I searched volvoforums.com but couldn't find anything definitive until I ran across the following post on another forum: Volvo S70 Starting Problems - Car Forums - Edmunds

That poster wrote the following, which caught my attention:

"Repair items which made no difference:
new fuel filter - located by passengers rear tire = $30.
new spark plugs - located engine center under top cover plate (Bosch +4) = $35.
new battery = $65. - love that squeeze type connector.
sensor MAF mass air flow:
located in top corner of intake air filter box.
yes engine will stall when repluging in connector - shows it is working.."

This is the typical list of things replaced by others suffering from a nonstarting Volvo throughout volvoforums.com. However, at the end of the post he wrote:

"I installed new water temperature sensors, problem solved, very easy to do."

This sensor is less than $35 at AutoZone. I bought one just to see what would happen. It started right up. Wow.

Then it stopped starting five days ago, and I'm back to square one. I've got a Haynes manual coming from Amazon and bought a yellowed, dusty Chilton's from a forgotten corner of my local NAPA store. It's not great, but it lists maybe a dozen sensors that eventually plug into the "Engine Control Module." If any of those +/-12 sensors is bad or off or unplugged or whatever, the car won't start.

It is logical to look at fuel, ignition, and air to determine why a car won't start, but I never *imagined* I'd need to replace the coolant temperature sensor to get a car to start. This is nuts.

Since starting problems are chronic problems with Volvos, is there not a rational protocol developed somewhere to quickly determine which sensor is in error?

 

My protocol for a no start would first be to check for stored trouble codes, then check for fuel and spark. No spark is often a cam position sensor (which will usually also set a DTC) and no fuel could be several problems, commonly a fuel pump relay. It is not true that every sensor being unplugged will cause a no start, only some of them. The ECU will revert to either a limp mode, or a alpha-N mode (like when you unplug the MAF) to continue operation with some signals lost or out of operational range. This situation would also be accompanied by a DTC.

Possibly your coolant temp sensor was not the problem, and there is some other intermittent issue that just happened to solve itself temporarily and confuse you.

Like you say, you need to look for fuel, spark, and air to determine which is missing and from there you can narrow down the problem, whether it is a sensor or something as simple as an loose distributor lead. No number of online guides can replace common diagnostics.

 

what size hex bolts should i replace the torx with? the inner one is already rounded out and stripped, im pretty sure the part it screws into is stripped also. !@#$

 

chisel the head of the torx off. pliers or sometimes your fingers will get it out, after you remove the housing of course, which requires chiseling the head off the torx. As i recall it was a m6 X something.

 

If you can get one out then all you'd need to do is match it up. If it's stripped then you're going to have to find a way to get it out and either drill and tap or heli-coil it.
First see if you can get one out. Drill, chisel, file or grind the striped one off and do your best to get the other out in one piece so you have something to shop for. Try to soak them down with a penetrant. I like PB Blaster myself.