2005 XC70 Coolant Intermitent Leak

[geminiys]

I am little puzzled here and looking for some possible ideas why I have what I have and how to fix it.
The car has been purchased a few years back with 136k on the dial in good condition and records indicated that Timing Belt was changed at 126k but Water Pump change is unknown. The car is driven by my dad, roughly 5-7k a year and already twice in last 2 years he has experienced Coolant Dump phenomena. The coolant level is very stable and shows no indication of been leaking when checked on regular basis but already twice in 2 years the Expansion Tank went completely empty with no puddle under the car when moved from the parking slot. On my further investigation first time, a year ago I saw coolant stains all over the Oil Filter housing from under the car and traced it to some where in the upper area above the Oil Filter Housing but couldn't point to the exact area of the source. The second time is in question, as I haven't looked at the car yet but will tomorrow. One thing I am curtained in is that Expansion Tank and hose to it is good and the leak is coming from the front of the engine, potentially around Water Pump (Thermostat Housing is good and dry).
One thing I don't really understand is why the leak only happens once in a long period of time and has a signature of a dump rather than a continues leak and it looks like it happens only while the car is in motion (no puddle under the car when car is pulled from a parking slot (always the same slot). Question: What could be causing intermittent leak like that and what is the remedy?
Thank you in advance for all the help.

[abscate]

It didn't go empty suddenly, you just find it that way one day. That's why there is no puddle.

When the coolant level goes low, do you get a warning light on the dash?

Hoses, heater core, head gasket are all things which can seep coolant unnoticed until you run out.

Start checking the coolant tank weekly until you understand the behavior. I'll bet it isn't dumping suddenly

[oragex]

There might be a crack or a loose hose clamp somewhere. As abscale asked, was there a low coolant message before this happened? This would indicate that the coolant was leaking while the car was driving so there would be no puddle once the car is parked because the coolant is already gone. Could it be that when the leak happened, the car just have been hard revved? The expansion tank may also crack and may leak only when over-pressurized, check it again you can disconnect the sensor plug and lift the tank. Also check the cap and the seal (reverse the seal if needed).

Normally we replace the original water pump only at the second timing belt.

[geminiys]

It didn't go empty suddenly, you just find it that way one day. That's why there is no puddle.

When the coolant level goes low, do you get a warning light on the dash?

Hoses, heater core, head gasket are all things which can seep coolant unnoticed until you run out.

Start checking the coolant tank weekly until you understand the behavior. I'll bet it isn't dumping suddenly

There might be a crack or a loose hose clamp somewhere. As abscale asked, was there a low coolant message before this happened? This would indicate that the coolant was leaking while the car was driving so there would be no puddle once the car is parked because the coolant is already gone. Could it be that when the leak happened, the car just have been hard revved? The expansion tank may also crack and may leak only when over-pressurized, check it again you can disconnect the sensor plug and lift the tank. Also check the cap and the seal (reverse the seal if needed).

Normally we replace the original water pump only at the second timing belt.

Thank you oragex and abscate for responding. I told my dad to monitor the Expansion Tank coolant level on daily basis and he does it since the first time it happened. But again, all is good and suddenly one day all is gone. He has never mentioned about any messages popping out on the dashboard, even though he knows that these messages do exist. The leak happens in the front area on the engine, as I mentioned before the Oil Housing has stains of coolant and they weren't present at the time of purchase when I checked. Therefore Expansion Tank is not cracked but I will check again to make sure.
I haven't looked yet but is there a good write up on how to replace a Water Pump on these cars if I decide to go with it? I am a DIY but never worked on new style Volvo yet.

Thanks

[oragex]

A wp check is relatively easy. The side-plastic cover over the timing belt has a recessed 10mm bolt on top. The upper cover is clipped and can be pulled a bit to free the side cover. Or you can remove it with two torx screws.

On this P2 model, we normally don't replace the pump on the first belt, only on the second one. However, some places are not aware and might replace the pump. I have read more than once about aftermarket pumps that filed very early (and catastrophically). Replacement must be Aisin. To make some place the coolant and steering tanks can be lifted up after disconnecting the coolant sensor (it's fragile). The coolant drain is in a hole under the bumper drivers side.

http://forums.swedespeed.com/showthread ... eplacement

[geminiys]

I am back with the intermittent Coolant Leak.
I have removed the TB Cover and found that WP is dry and no residue present of a Coolant Leak. I have also inspected the T-stat and it is dry too. The Expansion Tank and cooling hoses are in good shape and have no coolant residue present. The leak happened twice now where after driving the car it was parked and the next morning a little puddle was found behind front passenger wheel. According to Expansion Tank the the level was decreased from near Max to the middle between Max and Min. The next morning the same happened after driving it and the level went from the middle to Min level. After adding coolant to the middle mark no leaks for several days now.
Question comes: Is there some kind of release valve (unlikely but worth asking anyway) present in the area underneath the T-Stat housing and behind a Steering Pump/Alternator?
Is it possible I have a tiny crack in the front area of the engine block?
Is it possible Head Gasket has a crack and leaking to the outside the block (never heard it before but...)?
My last reserve is to remove Steering Pump and possibly Alternator to investigate the leak further because it does look like coming from that area, as bottom plastic cover has coolant drips in there and filter housing has coolant residue present.
Any help and/or advise is greatly appreciated.

[mcq]

We had a similar issue on a 99 xc. Had it in the shop 2-3 times. Two issues. The expansion developed a tiny crack in it, but seemed to leak intermittently, made no sense, but I pulled it out and saw coolant on the bottom. Also found the reservoir cap developed a tiny leak, again seemed only to leak occasionally. does yours leak with or with/ out heat on? Also Old head gaskets can have very tiny leaks. good luck

[skippy]

I am having the same issue with our 2001 v70xc. Coolant dripping from the oil filter cover as well as running down along the front of the oil pan. It seems to be coming from the front of the engine block but I can't tell exactly where. It also seems to be more prevalent when the engine is cold. Came out this morning and you could see the af dripping. Might just be because it has had some time to leak though. My fear is a crack in the block. I just replaced the head gasket so I don't think it is that but could be if I screwed something up. Although I tested for carbon in the expansion tank and everything came out negative. I guess there could be a leak from the cooling chambers to the outside of the engine if the gasket didn't seal properly. Any luck finding your issue? I'll keep you updated when I find mine.

[KurtL]

On a car this old I would just replace the expansion tank for peace of mind. I developed a leak in my 01 V70 tank so I replaced it with a new OEM one. I am thinking of doing the same in my 08 C30.

[abscate]

Much more likely to be an intermittent leak in hoses or reservoir than a block leak. Be optimistic. Just drive it, monitor coolant level weekly until it rears its ugly head and shows you its spots