850R starting issues when hot. Radiator fan running constantly

[Volvovlo]

Hi guys,

About 18 months ago, I had a very similar problem where my car would start fine cold, run all day long but once it switched off, couldn't be restarted until the engine cooled down. To fix this, I replaced the camshaft sensor with a used one which seemed to fix the problem until the other day.

Now I have strangely similar problem, whereby after towing a trailer a short distance one day (about 700kgs weight, not sure if this is related to the problem), turn the car off and try to restart, it barely idles and sputters and revs low for a while (As if the large turbo pipe has popped off, had this before, exact same symptoms) but then comes right. Checked all the pipes, everything seems okay. The next day, the symptoms change. Now the car starts easily when cold, with the exception of the radiator fan running constantly. Runs perfectly all day until I turn it off. Sometimes it restarts, other times it wont. (although persisting with a can of engine start usually brings it to life). The CEL is on, but unfortunately there's a fault with the wiring somewhere as my cars ECU can't be read so I'm unable to get the codes.

Just wondering where to start. I heard the temp sensor, or fuel relay are good places to start. Also wondering if its possibly the camshaft sensor again? I had a brand new battery installed 6 months ago so don't need to worry about that

1996 850R.
290,000km

Cheers.

[scot850]

I would check the temp sensor and the wiring. There are resistance values somewhere on MVS which relate to ambient temperature.

If the sensor is bad, the car may think it is not up to temp and be flooding the car on start up. This can also cause the engine fan to run all the time as well.

Also check the connector on the back of the power steering pump. The connector and wires can go bad.

There is also a fan relay above the radiator below the shroud. Again, check the wires to this and the connectors for corrosion and breakage. The relay does also fail.

Neil.

[rrres]

Start with the above suggestion of checking the temp sensor. Typically, when a fan remains on, the ect could be bad.

Next, I would check the o2 sensor. Just this week, I fouled the afr/o2 sensor on my 99 after doing a berrymans piston soak and wet compression test. I started the car and smoke was coming out of the tailpipe from the residual oil and berrymans. This fouled the o2 sensor and the car was misfiring and idling rough afterwards. CEL turned on and there was an oxygen sensor code. The fan also was running constantly, even after I turned the key to off. I couldn't really feel the misfire at normal driving speeds...only at idle. Replaced the afr/o2 sensor and that solved it.

Maybe your engine went rich during the trailer tow and fouled the o2 sensor. ??