Sanity check: Volvo cooling system content

2006 Volvo V50 T5 AWD. Driving home tonight in one of the worst rounds of commuter traffic I've seen in a while, all seemed normal until I finally broke out and was able to achieve some normal speeds, at which point I noticed my heat was going away slowly (40F ambient). Looked at the temp gauge and saw it had dipped a tick below halfway. Pulled over ASAP, fearing that something had blown up and I'd dumped all the coolant, but no - everything dry, coolant in the expansion tank, some pressure in the system (but less than one would expect after an hour of driving). Closed the hood and drove home. Under throttle or at idle, temp is normal; driving at low or no load and it dips.

I'm thinking the thermostat is stuck open, but I'm also exhausted and not entirely sure I'm thinking straight. Before I pull the trigger on parts, can someone please confirm or deny my diagnosis? It has been a long day, and this is most assuredly not what I needed to end it.

About two years ago, I noticed that I wasn't getting any heat out of my 1998 V70R. I drained the coolant and swapped in a new thermostat. The date on the old thermostat indicated that it was original to the car, even though the shop that did the timing belt said they replaced it six months earlier. 

Well, that's a lovely surprise. I'm going to order the whole housing - the car has 208k miles on it, and I don't trust plastic that old to survive handling. Thanks.

If I recall correctly, one of the bolts was a little hard to access squarely and I had to use a few gentle taps with an impact driver to break the bolts free of the aluminum head. 

That was also the second time that the timing belt had been changed. 

In reply to Woody (Forum Supportum) :

From your description, I'm wondering if the thermostat location is different on your V70R and my V50. Mine is at the back end of the engine, down fairly low near the bell housing, under the intake manifold. I haven't been in there yet, but it looks like it shouldn't be too bad once I get a few things out of the way.

It does sound like the thermostat stuck open.  If so, when you start it in the morning, It will take a while to get warm

In reply to jfryjfry :

For the moment, I'm going to deadline the car unless I need it. Parts are on order. I'm just glad this happened now and not in a couple months when it's freezing.

Parts showed up a few days ago, and today was my window for getting it fixed. After cursing the person who designed the airbox for a while, I finally got access to the offending thermostat. Because I was draining the cooling system anyway, I figured I'd replace the octopus hose while I was in there. It hadn't shown any signs of leakage, but I had no idea if or when it had been replaced. I popped the new thermostat housing in and confirmed that the old one had failed open, then started on the hose. For the uninitiated, this thing has no fewer than five outlets, connecting the thermostat, block, lower radiator, and transmission cooler (in and out). I was a bit surprised to find that the new Volvo-packaged hose was made by Gates.

Unfortunately, in the process I managed to snap the plastic fitting on the hose that connects the pressure tank to the cylinder head, so I'm going to have to wait to test it, but everything else is back together. To add insult to injury, while the failed thermostat was indeed original to the car (2006), the octopus hose was date-coded 2016, so I didn't really need to replace it. No good deed goes unpunished.

After reconnecting the battery (the whole "key in Position II" procedure still freaks me out, since the electrical system springs to life the instant the negative terminal is connected, and it always sparks) I did start the car very briefly, just to make sure I hadn't missed any electrical connections or any other bits - all seems well, no CEL, no issues. I'll run over to FCP Euro Monday morning and grab the part, and hopefully have the thing back on the road by Monday afternoon.

Ran to FCP Euro this morning to grab the part. First time I've done the customer pickup there - it's impressive, both in size and efficiency. Find your name on the list, they pop open one of the wall of lockers, and you get your parts. Lots of interesting Euro stuff in the parking lot - I felt a little bad about driving the Miata.

Anyway, the new hose went in fine. I buttoned everything up and started filling the system...and heard splashing from the general direction of the ground. Looked underneath and, sure enough, it's leaking out. Rip everything apart again and discover the temp sensor in the thermostat housing wasn't fully seated. Fixed that and started Round 2. This time the liquid stayed in the engine. Idled for a while, then took it for a test drive, which showed the problem fixed. Everything stayed dry. I have declared victory - I just hope it lasts.

I had the exact same experience with FCP Euro local pickup - it was a great experience. Your symptoms matched what I've seen for a thermostat that's stuck open, so I'm glad you solved the problem. 
 

Must be a Swedish car thing, the t-stat housing on my 9-3 had a ton of outlets, as well. I started pro-actively replacing non-leaking parts that were scaring me, and after replacing those, I have real leaks from parts I didn't replace (heater hoses, water pump, and coolant pipe o-rings). About to load the parts cannon again, and the work will not be fun (especially the water pump). The joys of car ownership!

In reply to dj06482 (Forum Supporter) :

I considered just doing all the hoses in one shot, but I'm already pressed for time. Fortunately, the remaining hoses look to be fairly straightforward. The water pump will get done with the timing belt when the interval comes up in 2025.

Of course, the car has developed a new (unrelated) noise: a sort of popping on acceleration from the right front. I replaced the failed motor mount on that side while I had the expansion tank moved, so I'm telling myself that's where it's coming from. It's just the new part settling in. Yeah, that's it....

Because nothing can ever be simple, I'm apparently not done with this job. I was checking something under the hood yesterday and noticed that the coolant had dropped a bit. I had already topped it once after filling, which I assumed was just residual air moving out of the block and into the expansion tank, but this seemed unusual, so I looked around and discovered some suspicious looking spots in the area around the thermostat. It was enough that I decided to yank the airbox again and inspect; unfortunately, I found that it was, in fact, leaking. All the hose connections and the bolts holding it to the block are tight, and the spray pattern of the droplets didn't fit with those anyway. The only plausible source is the temperature sensor. For reference:

The sender is a press-fit into the recess on the upper right in the first photo, and is retained by the clip. When I wiggled the sensor I could tell there was up-and-down movement with the clip in place, and the clip itself was not very tight. I pulled the sensor out and inspected the O-ring as well as the recess - everything looked OK (it's all new parts, Volvo OE housing and Facet sensor), but the O-ring was not sitting squarely in the bore, which I'm assuming is what is causing the problem. I pinched the clip a bit to snug it up, which worked fine, but the only way I could restrict the up-and-down movement was to add another O-ring as a spacer. Unfortunately, even though it feels much tighter now, it still seems to be leaking once the system is pressurized.

I'm going to call FCP Euro tomorrow and see about options. I'm inclined to think the O-ring that came with the Facet sensor is the issue, but if anyone has any other brilliant ideas, I'm all ears.

+1 for calling FCP Euro and seeing if they have any suggestions. Any reports of similar issues (and hopefully solutions) on the Volvo forums?

Seems like that clip is a strange way to retain a sensor in a pressurized system, but I'm far from an engineer.

Well, bonus points to FCP Euro. I called this morning, and while the rep I spoke with couldn't help me, he forwarded my request to speak with one of their Volvo guys. While I didn't get the callback I was expecting, I did get an after-hours email that suggested trying another brand of sender (FAE), which is what I was considering. What I did not expect is that I was provided with an account credit to cover the part and shipping; I made no request for any such thing, and was quite surprised when I read the email. I've put the order in, and hopefully the new part will be the solution. Failing that, I'll try an overpriced OE Volvo O-ring, and if that doesn't do it, I may have to consider an aftermarket aluminum housing.

Installed the FAE sender this afternoon. After a test drive to get it hot, I looked it over and everything seemed to be dry, so I'm tentatively calling this solved. I'll be checking after every drive this week, just to satisfy my cooling system paranoia (no level sensor on these cars, which is irksome).

Good job!