V70 P2 Engine probs

[MattV70]

While cruising along down the M5 this weekend my car's developed a bit of a problem. It feels like a miss-fire, as in the car slows momentarily, and then sort of catches up again, all within the space of a second, so it's only just noticable. I had cruise control on, so it wasn't me tapping the throttle, and it only happens when the air con is on.

When the air con is turned on the temp rises very slightly to approx half on the scale, but never goes any higher. Could it be the ecu backing off the power due to heat? It only happens every 10 - 15 mins, and the outside air temp was only 23°C. It has enough water / coolant.

Where on the temp guage should the needle be when cruising at 80 - 85? Is it running hot and in need of a rad flush?

Any help would be appretiated as i don't want to leave this to develop into a costly problem later!

Cheers

Matt

[V8guitar]

Don't know the answer but my temp gauge rises to half way and stays there no matter what.
I guess the obvious is to check your levels first....

[MattV70]

If yours sticks on half all of the time, mine with air-con on is the same. It drops off slightly when the air-con is off. I didn't think it was overheating as i'd expect the guage to move further, and i'd have thought that it wouldn't be showing the fault while cruising at 80 with all of that air rushing through the rad!

[Martinr]

Matt

I have had this with the aircon and cruise on together. It is caused by the increased load when the compressor cuts in.

Mine is short cycling at the moment so the car feels like it is missing a beat as it only stays in for 1 or 2 seconds at a time, turn off the aircon and all is fine. I don't think it is a problem.

Regarding the temp guage. Mine goes to halfway and stays there even when cruising 200 miles at 70-85 mph.

Only time it ever went above halfway was last winter when the thermostat failed in the closed position. Luckily it happened on the coldest night of the year so I had no other problem as a result.

If yours isn't reaching halfway in normal operation I would suspect the thermostat is sticking in the open position and your car is running a little on the cool side. Replace it they are only about a fiver.

[MattV70]

Cheers Martin. It's good to know that mine isn't the only one that does it, and even better than that it won't be too expensive!

I'll swap the thermostat over when i get the chance.

Thanks again

Matt

[stuAWD]

It looks like this a common problem, mine does it when the AC is on at speeds above 65 ( not noticed it happen below 65). It's just like an occasional single misfire on one cylinder. Dosn't happen with the AC off.

[V8guitar]

I haven't noticed this, but I'll check tonight....

[V8guitar]

Sorry to worry you guys but mine doesn't noticably do this...yes you can feel the edge is taken off the performance slightly with the load from the Ac but its not intermittant, ie slowing and speeding up