2008 XC70 -- Intermittent overheating

[mtd240]

Hi all -- I'm hoping to get some pointers on how to diagnose an issue on my father's 2008 XC70 (3.2L I6, 101k miles). I have maintained it since he purchased ~2 years and 20k miles ago, but I don't drive it regularly so I only know what he has told me:

1. The A/C doesn't work unless he is at speed (blows warm at idle)
2. The radiator fans don't turn on when they should (e.g., idling in traffic with the A/C on max). They do turn on for a few seconds on startup and often turn on and stay on for a couple minutes after he shuts off the engine.
3. If in heavy traffic, he has gotten the High Temp warning.
4. It threw a P0128 ("Coolant temperature below thermostat regulating temperature") yesterday.

My first assumption was the fan controller - I shouldn't have fired the parts cannon, because that was expensive and didn't fix the issue. But, it seems like something isn't telling the fans to turn on when they're supposed to be on. Clearly they work (mechanically) based on #2 above.

I've read that thermostats are a common issue on these engines -- plastic tabs breaking and locking it closed -- but I'm not sure I see how that would result in the fans not operating properly.

Any help/guidance would be greatly appreciated! Note that I don't have VIDA/DiCE -- I need non-OE tests if possible.

[pgill]

MTD240,

You are on the right path.

Some things to consider.

The small wire at the fan controller sends a signal to the fan controller (a PWM signal if you know what that is) that tells the fan to turn on

Lets take a look at the XC70s first cousin
Another P3 that you may not be aware of

Broken small wire

https://www.freel2.com/forum/topic37115 ... =blue+wire

https://www.freel2.com/forum/topic31727 ... g&start=15



Another possibility is the ground wire, if you don't have a good ground connection then the fan controller may not interpret the PWM signal correctly.

If you know how to back probe the black wire at the fan controller then measure the voltage drop from it to Battery (-) with the fan running, the fan must be running.

If the Voltage drop is 0.100 Volts or less then the ground connection should be fine.

If the Voltage drop is above that especially if it is over 1.0 Volts then your problem may be just the poor ground connection.




As for the Thermostat yes you should replace it.


Note: I replaced the Fan in my LR2 with an actual Volvo Fan (single to dual Fan upgrade) when the single fan failed the first thing I noticed was the loss of AC at idle. And I replaced the Thermostat before it failed on my LR2.

As for my S80 I have a long thread of what I've done to it here on MVS


Take care

Paul

2008 LR2 3.2 P3 Platform (My first "VOLVO" wasn't actually made by Volvo)
2010 S80 3.2 P3 Platform (My first actual Volvo)

[mtd240]

The small wire at the fan controller sends a signal to the fan controller (a PWM signal if you know what that is) that tells the fan to turn on

Lets take a look at the XC70s first cousin
Another P3 that you may not be aware of

Broken small wire

https://www.freel2.com/forum/topic37115 ... =blue+wire

https://www.freel2.com/forum/topic31727 ... g&start=15

Another possibility is the ground wire, if you don't have a good ground connection then the fan controller may not interpret the PWM signal correctly.

If you know how to back probe the black wire at the fan controller then measure the voltage drop from it to Battery (-) with the fan running, the fan must be running.

If the Voltage drop is 0.100 Volts or less then the ground connection should be fine.

If the Voltage drop is above that especially if it is over 1.0 Volts then your problem may be just the poor ground connection.

Okay -- so I should probably check the fan wiring. Do you happen to have a wiring diagram for an '08 XC70 (or know of a place I can get one without emptying my wallet)?

As for the Thermostat yes you should replace it.

Are you saying you think the thermostat could cause this sort of behavior? Or just that it would be good practice to change it now, particularly since they are a common failure point on this car ~100k miles?

Thanks!
Michael

[pgill]

The Thermostat assembly includes the PTC that the ECU uses to measure the engine temperature. And the ECU turn on the FAN using the temperature it measures at the PTC.

It is possible that the Thermostat failed open instead of closed (the thermostat is very complex)

So a failed Thermostat that allows full flow to the radiator all of the time may inhibit the running of the cooling fan until you shut off the engine and it gets hot as it heat soaks from the cats. This would do what you have experience. (no fan until you shut down)

However the Fan should always run with the AC turned on so the Thermostat won't fix that problem.

Get a quality Thermostat from VOLVO or LAND ROVER don't buy aftermarket.

If I were you I would fix the Thermostat immediately and then work on the cooling fan.

I can show you a link to a LR2 owner with a failed head gasket due to over heating (I don't recommend that you take that path)


Good luck

Paul

PS I think I found a S80 wiring diagram somewhere but I can't remember where, I will reply again if I can find the source