I have a coolant leak at the rear of the engine. Of course with everything stuffed between the engine and firewall this is difficult to diagnose and repair.

It looks like the leak is coming from the water pipe that connects to the back of the block using a nipple. It's difficult to even look at this area, and I broke the connector off of the cam phase sensor trying to figure out how I was going to get tools on this fitting.

Any advice for working on this pipe/fitting, or maybe I missed something and the leak could be from another connection?

BTW this one is rather interesting. It only leaks when it is hot, it will hold 20psi all day long cold.

Edit: I'm a doof! The car is a 98 S90 (964)

 

what year & model?

 

i had mine leaking from the connector valve between the heater core and the engine. was dripping down and looked like a freeze plug. i would double check these 3/2 hoses first. i can shot a pic your way if u need help understanding my horrable discription

 

I really slipped up there, updated my first post to note this is a 98 960

I have experienced the leaking water valve. That hose between the engine and valve was also leaking so I replaced both hoses. A few years ago I used a water valve from a ford van to replace the plastic leaky one.

My leak is coming off the bellhousing and dripping on the exhaust. Since I had leaky hoses I cleaned all the coolant residue off and it looks like the leak is coming from that pipe that connects the block to the heater hose. My concerns about other possible leaks from the back of the engine are the head gasket and a water temperature sensor back there. It's really hard to get a mirror down there to check this area out.

So I am still thinking it is that flared pipe connected to the block with the male-male nipple. All I know about this is I have to use the thread sealer on it. I wish I knew which side of the nipple was leaking or if I could try to tighten the flare nut and nipple. I don't know what size tools fit on them nor do I have any idea about torque specs.

 

i may be wrong but i dont think the 98 had a temp sensor on the back of the engine. just the one under the thermostat, as for the head leaking, i would check the oil (for coolant contamination/milky) and the coolant for gas fumes.I would say its prob the old hose, hope this helps.

 

correct - only one temp switch in stat housing
sounds like a leaking head gasket to me
thats how I became a 960 owner at 89k miles because the customer did not want to fix this - now I'm at 210k and running ever so fine!

 

Temp sensor by the thermostat at the front of the engine operates the instrument panel gauge.

In VIDA in section 21 "Engine: Replacement of engine / Transferring external components" there is a photo of the rear of the engine without the flywheel. It points out a temperature sensor in the rear of the cylinder head, and the 97-98 wiring diagram shows this too. This sensor is used by Motronic.




So all in the same place you have this water pipe to feed the heater hose, then directly above it the joint between head/block and then in the head this temperature sensor which I don't know if is even exposed to water.

Somehow coolant residue is getting on the flare nut of the pipe and running down the bellhousing on the exhaust side.

I am considering also that it may be the head gasket, but this is again interesting as there is definitely no contamination of the coolant and I have not detected anything in the oil. This situation makes me want to send an oil sample to the lab, but I changed the oil recently and there was no water in it. There are no signs of condensation looking under and into the oil cap but the flame trap looks funny yet doesn't smell like coolant. Don't know what to make of that but I'm sure the oil box stuff is not in great shape.

 

1995 and later 960's use the temp switch in the thermostat housing for the temp gage & fuel injection - up to 1994 they used 2 switches. It's common for the head gasket to leak coolant externally at the right rear corner for some reason - unless it overheats - then it gets real ugly.

 

You guys are right, I can't find the sensor in the rear that the volvo wiring diagram shows. Changing the head gasket is not going to be fun, for starters I do not have the tools required to set the timing. Maybe an inspection camera will help me verify this.

 

The coolant leak got worse to the point where it was eating 4 oz a day so we took it out of service 25k miles after starting to have to add coolant on a regular basis.

I got the head off and can see the coolant leak path to the rear of the engine housing in the cylinder head gasket. Interesting they used a head gasket that gets eaten by coolant.

With the head off I can access the nipple. The crank position sensor and nipple interfere with each other. Compared to the service instructions, my 98 does not have a temperature sensor (as mentioned) nor a ground wire on the back of the head.

On the tube nut a 15/16 wrench has a nice fit and a 24mm feels kind of loose. On the nipple itself a 22mm wrench feels ok and a 7/8 is the second choice.