DIY: 2005 Volvo XC90 Thermostat + ECT without removing PS Pump

[cn90]

DIY: 2005 Volvo XC90 Thermostat + ECT without removing PS Pump

Car is 2005 Volvo XC90 with 105K miles, cabin barely warm in winter. Tstat is original, so it is overdue.

- Volvo does not sell Tstat alone (some forums say it may be Gates TH35991 which may require modification before install), instead you have to buy the whole tstat assembly which includes: lower housing, upper housing, tstat itself, and ECT sensor.
- I also took photos of the tstat itself in case anyone finds this item sold separately, please post for the sake of humanity!

- To replace the whole assembly, you have to unmount the PS Pump to get access to the LOWER housing bolts. This requires sepcial (Torx) serpentine belt tool and all that jazz. I will show a quick and easy way to do this WITHOUT dismounting the PS Pump.
- All you have to do is replace: Upper Housing, Tstat itself and ECT (which is a good practice b/c most ECT fails around 100K-120K or so).


PARTS/TOOLS:

- Volvo PN 31293698: online Wahler is $100 or so, Volvo dealer is $110 or so.
- A small clamp for the small hose as it is Oetiker type and will be damaged during removal.

- Torx 30 key for Upper Bolt; 1/4" extension + flex joint + T30 socket for Lower Bolt.
- One 19-mm socket.

- About 1/2 gallon of Prestone 50-50 coolant.
- Telescopic magnet b/c chances are you will drop something!
- Antiseize
- Dental Floss

PROCEDURE:

1. You can drain coolant if you wish, I did not.

2. Spray the Bolts ahead of time with PB Blaster, then remove them.
Trick: Place a rag below to catch any bolts that fall off.

3. Once the bolts come off, stuff a rag inside so during cleaning of mating surface, debris does not get inside the housing. If you decide the re-use the Upper Housing, then clean it with fine sand paper. If you replace the Upper Housing, then undo the Oetiker clamp on the small hose. Whatever you do, these hoses form a bond and you need to slowly pry them off without damaging them. GO SLOW!

4. To replace the ECT: use a Pick tool and pry as shown (look at the new ECT sensor as a guide), then use 19-mm socket to remove it. Make sure you remove the old washer! I use antiseize on the ECT threads as well as the T30 bolts.

5. During install, it is VERY TRICKY b/c of the tight space but you can do it!
- Play with the new tstat and dry-fit it: you will see that even if everything fits correctly, there is a gap of 5mm between the housings. Don’t panic, it is normal: the two (2) T30 bolts will tighten it down. So, again play with the new assembly and you will see what I mean.
- First I tried dental floss around the gasket + tstat to help hold them in place: FAILED attempt (see photo)!

- Then I improvised and this worked great:
* Place tstat in Lower Housing.
* Starbucks bamboo coffee stirrer to temporarily hold the gasket in place.
* Dental Floss helps holding the tstat pin horizontal, once the Upper Housing goes in nicely with a gap of 5mm, keep pressure on the Upper Housing, then remove dental floss.

- Install the two (2) bolts, making sure the gasket sits properly.
Anyway, you will find this very last step #5 challenging but you can do it.
Of course, the kosher way is dismounting the PS Pump but I was not interested in the kosher way.

6. Refill with 50-50 coolant and go for test drive. Then check for any coolant leak and coolant level in the reservoir etc.
That is it boys and girls...

[cn90]

UPDATE: Test drive revealed no heat in the cabin...LOL.

Then I remember:
- I pulled on the dental floss a tad too high.
- During re-installation, I had the upper radiator hose attached (I was "lazy" and attached the hose to the new upper housing ahead of time!), so I didn't have a clear view how it came together.

No worry, easy fix:

1. If you replace the tstat this way (w/o removing PS Pump), make sure you leave the upper radiator hose UNATTACHED during re-installation so you have a clear view of what is going on.
Always play with the new parts to have an idea how it fits together.

2. For me the fix was easy: to minimize coolant loss, I used a rag and vise-grip and GENTLY clamp the hose from reservoir. Then 7-mm wrench to release the clamp.

3. Once the upper radiator hose is out, it is obvious that the tstat pin was in the wrong place!
- I loosened the LOWER bolt a few turns, but do NOT remove it.
- Remove the UPPER bolt.
- Adjust so the pin is dead center.
- Check to be sure gasket is still in correct place.
- Re-install bolts, then remove rag + vise-grip and refill with coolant.

Test drive the car.

So, if you leave the upper rad hose unattached during re-installation, it is a very very easy job!

[dono]

I have to laugh at the creative solution vs. the proper install. I did the job yesterday on my 2004 V70 AWD Turbo Wagon (using the correct procedure). I laugh not to mock but to admire the lengths you went to to avoid replacing the full housing (and having to remove the steering pump/drain a few liters of coolant). If I had read this before Id probably have seriously considered your method.

In a like-minded spirit I got as far as disassembling the new housing to see if I could pop just the thermostat in the old lower housing and realized the fitment would be a problem because the new genuine volvo part now has the pin you noted (the 2004 original part on my V70 had no pin). I wasnt clever enough to consider dental floss and Starbuchs stirrer (lol). Also the new part I had did not have a breather on the thermo so I considered the new part a new design and felt mixing parts could be problematic functionally. There are a lot of systems downstream/reliant on the thermo and sensor in the engine management and I didnt want potential variation in the function of this system.

Besides mixing an old part with a newly designed part, another potential issue in your shortcut is you do not get a new seal on the bottom of the housing - these do fail. So you might have to remove all this in the near future to replace the seal if it begins to leak .

[cn90]

Re mixing new parts and old parts: no worry!

I also have a 1998 Volvo S70 GLT with 185K miles: The setup is similar: Upper and Lower Tstat Housings. The only thing new in that car is thermostat every 70K miles and the ECT was replaced at 110K. Other than those 2 items, the Upper and Lower Tstat Housings are still stock at 19y/185K later.
Absolutely no leak.

BTW, I keep the remaining parts (Lower Housing and the metal gasket for the 2005 XC90), just in case I need it later, but I doubt I will ever need to use these parts. The experience with the Volvo 850, S70 showed that the Lower Housing and the metal gasket lasted some 300K miles.
If I have it my way, I'd rather buy the thermostat and ECT separately, but that is not an option for the 2.5T engine, unless someone comes up with an alternative. This is why I bought the whole assembly by Wahler and used ONLY what I needed.

[cn90]

...I laugh not to mock but to admire the lengths you went to to avoid replacing the full housing (and having to remove the steering pump/drain a few liters of coolant). If I had read this before Id probably have seriously considered your method...

LOL,

To be honest with you, if I have to do this again (replacing ONLY tstat and the ECT as in the write-up), I can do the whole thing in 20-30 minutes max, now that I learned from my mistakes (simply b/c there was no write-up like this in many forums I browsed).

There is nothing to it: these are the steps:
- Undo the large radiator hose from the Upper Housing.
- Undo the 2 Torx bolts.
- Undo the small coolant hose.
- Clean mating surfaces, you can re-use the Upper Housing or use a new one, it does not matter.
- Replace thermostat: 15-second job.
- Replace ECT: 1-minue job.
- Put the Upper Housing back with new gasket, making sure the tstat pin is centered.
- The rest is straightforward.

Easy Peasy...

[oragex]

1/4" extension + flex joint + T30 socket for Lower Bolt is the key word for this DIY.

I did mine without a flex joint and with the PS pump tossed (easy to toss away actually and I recommend for this job). The two torx bolts are quite tight on the t-stat housing, watch not to strip them. I used a locking pliers on the lower one to break it loose. Once removed, I replaced them with regular hex head bolts, not sure it was M8

Also recommend disconnecting the upper hose at the t-stat, try catching the coolant so it doesn't leak on the alternator.

[cn90]

UPDATE: if you replace the tstat and still don't have good cabin heat, chances are the Heater Core is compromised.

Just replaced my Heater Core (Behr brand) and the heat is amazing.
The DIY is below:

DIY: 2005 XC90 Heater Core Replacement:
viewtopic.php?f=10&t=82726

[cuhfs]

Thanks for the great post!

[oragex]

UPDATE: if you replace the tstat and still don't have good cabin heat, chances are the Heater Core is compromised.

I have the same issue. In winter, the heat is not bad, but I've noticed every time I do a turn, a wave of much warmer air gets inside the cabin. I believe the heater core has a tendency to crack inside - it has some plastic separators to get the flow circulate throughout all the exchange surface. When these separators crack, the hot fluid won't completely fill the heater, causing lower temperatures in the cabin. Unfortunately, on the S60 replacing the heater core is quite harder than on the XC90. On the S60 the access to the clips securing the pipes is terrible, plus the steering column gets in the way when pulling the heater from there.

[cn90]

oragex,

The XC90 heater core procedure is easy as the steering column is further forward, so no issues at all.
The S60, check rspi's youtube video, he did not remove the steering column, so the new HC gets a "little scratch" during installation but no consequence at all.