98 V70XC humming noise only when on throttle and cold

dmcfan · Post by **dmcfan** » 31 Aug 2015, 12:00

I tried searching and based on the key word I get a lot of drivetrain results and I do not believe this is related to that.

I get a humming/rubbing noise that only occurs first thing in the morning and only if the car has sat for at least two days. I can get the noise if I jab the throttle while driving. I do not get it just sitting at idle.

The noise increases with the amount of throttle I apply but goes away as soon as I let off and coast.

This also only lasts a couple miles then never returns.

Any ideas of what to look at? I did notice if I put even the slightest amount of pressure on the timing cover it makes a similar sound. I was surprised at how little tolerance there was there.

Post by **abscate** » 31 Aug 2015, 12:17

I think there was a thread on the oil cooler thermostat singing a tune - down low near the oil pump in early P80s.

Post by **scot850** » 31 Aug 2015, 17:06

Another possibility is the SAS pump. If the car only does it when it is cold, chances are the pump is failing. If you have done the delete for the SAS pump then this may be the cause.

The reason the pumps fail is the valve up by the turbo fails and lets condensation run down into the pump. There is no drain hole so the pump fills with water and eventually seizes the bearings. Either remove the pipe from the valve where it enters the SAS pump and see if water comes out. If it does you may have caught it in time to save it. Remove it and drill an 1/8th" hole in the lowest part of the fan casing to allow water to drain out. Replace the valve up at the turbo. Or look up the SAS valve delete using a resistor and remove the SAS pump. The SAS pump only runs when the car is cold and vacuum (when you are on the gas) will make it noisier.

Neil.

dmcfan · Post by **dmcfan** » 01 Sep 2015, 04:47

Thanks for the replies. It seems like if it is the oil thermostat then a lot of people just deal with the noise with no adverse effects on the car.

No never did the delete. I was considering it to just eliminate that eventual problem. I will look for the instructions on that process you described. Is that write up in this forum or another one?

I would think if it was the pump I would hear the noise at start up immediately. It only does it once I am in drive and use the throttle.

Post by **rspi** » 01 Sep 2015, 05:40

I believe it's the oil thermostat. Only happens on cars that have the oil cooler lines that go to the radiator.

The air pump can actually trigger at any time. I had one kicking on 5 minutes into my drive with the car fully warmed up. It would be easy to check the pump, simply unplug it to see if the noise is still made.

I have a few of those oil thermostats if you need one.

Post by **scot850** » 01 Sep 2015, 10:48

Hi Robert, good input and it is worth hanging onto those oil thermostats as they are now obsolete! Either that or add them to the must pull list when at PnP.

I am adding to my list now and on completion of the rear sub-frame re-build will document the parts I came up against as now obsolete (like the large rear washer on the stay bar front mounting).

Neil.

Post by **Atis** » 25 Oct 2015, 15:02

Hello all, I have the same symptoms...
For me it seems that it is a noise that is proportional to the engine rpm and only comes if the car was sitting for some days or there was rain or wet weather.
I have tried to catch it, but it was really just a faint noise today. When it was standing for 5 days, the people on the street turned their had, it was so loud...
So here is the short video, you can hear it when I let off the gas.

All the pulleys and tensioners were changed 10k ago for OEM, TB is from INA, serpentine belt is Contitech and it was doing the same before the change.