Unlike what other naysayers have stated. Yes, you absolutely can upgrade the tank size to even the 71L or 18.8-gallon tank from the standard T5/T6 XC90. I know this because I’ve done it on my 2017 XC90 T8 Excellence. It isn’t even that difficult really, and apart from the larger fuel tank not all that many parts are needed.
Here’s what I did:
From a scrap yard I got the 71L tank from a standard XC90 (I believe the XC60 used the same tank as well). They are relatively easy to come by since the non-hybrid cars sold in much larger volumes. The tank I got came with the fuel pump/sending unit, although its plastic was very dry rotted and brittle. This tank also didn’t come with the heat shield for the exhaust, which I would recommend getting one with it, as the heat shield fits differently on the larger tank. Like I said mine didn’t come with the heat shield but I managed to make the original 50L tank heat shield fit.
From eBay I got a set of the 71L tank straps. They were much cheaper that way rather than getting brand new ones from Volvo.
I got the shorter retaining clips for the under-tank air shields. The air shields themselves fit just fine but you need shorter clips to fit the larger tank. These are P/N: 31383742 and 31383743. 4 of these are used on the vehicle or 2 on each side.
Those are all the parts you really need to complete this swap. I got a couple more of the heat shield and air shield retaining nuts but if the only ones are in decent shape they do not need to be replaced. I also reused my fuel pump/sending unit, and the electronic driver module for the pump. I do not know if there are any differences between the T5/T6 and T8 with these components, but since mine worked just fine I decided to stick with what I know worked. Also like I stated earlier the sending unit my tank came with was super brittle and weak. The only visual difference between the 71L sending unit and the 50L is that the 71L had longer rods on the top to reach further into the tank. I was able to swap one of these rods to my sending unit, but I would probably recommend getting the complete 71L sending unit with the longer rods.
To remove the old tank, I first ran the car down to about 10 miles to empty just so the tank would be mostly empty while I would be working with it. Before starting I put the vehicle in off-road mode to get as much height under there as possible. Once the vehicle was at the full height, I put the suspension in service mode so it didn’t adjust before I got the battery unhooked. Then of course unhook the 12v battery in the trunk, AND make sure you don’t latch the hatch or you’ll have a really bad day especially in my case with the Excellence where I couldn’t climb back there to hook the battery back up due to the divider. I had some drive-up ramps and I jacked the car up and put it on those ramps so I could get as much space under the vehicle as possible. Of course, a lift would be easier, but despite the fact I have an Excellence I’m more of a backyard mechanic lol.
I started by removing the under-tank air shields, and loosening the heat shield. Next, I had to lower the exhaust to have enough room to get the tank out. It would be easier to remove the exhaust entirely but I did not have a new gasket for the joint towards the front. I ended up removing the surrounds out of the bumper, and lowering the exhaust in the back. Don’t forget about the electronic emissions valve on the right side after the muffler, I forgot to unplug this and ended up mangling my connector from the exhaust hanging from it.
Next, I removed or loosened any visible fuel lines from the tank. There are two on the front left of the tank that the clips can be opened up and removed with only a pick tool. On the rear right side of the tank, I loosened the fuel filler neck connection, and the fuel pump driver electrical unit. In the center of the tank, you’ll have two coolant lines for the ERAD, and 2 large electrical connections for the ERAD. I did not disconnect the coolant lines at all, as they will have enough flexibility in them to remove the tank without disconnecting them. Some people might not agree with this next part but I disconnected the connector from the battery to the ERAD. I had the 12v disconnected so the vehicle was completely off but the High Voltage (HV) battery was still live. I was very careful with removing these connectors. There is a cable guard that holds these HV lines and this needs to be unbolted from the rear. There appears to be a communication connector which is a simple push clip to remove. The large connector, actually connected 2 large wires and was a bale style connector. I lifted the bale and assisted in pulling back the connector and the whole wire guard back, as it slides into tangs on the battery. Once this was disconnected, I opened up the cable guard with plastic slips and 2 T25 Torx screws. This allowed the wires to hang free and gave me much more flexibility to remove the tank. In the center of the tank where the wires were just off to the left side there is another fuel line connection that needs to be disconnected.
Once all these visible fuel line connections, and ERAD connections are disconnected the fuel tank straps can be removed. The tank will stay in place as there are 2 more bolts actually on the tank that hold it up. These 2 bolts can be removed next. Remember to hold up the tank while doing this. While holding the tank partially up the wiring for the fuel pump sending unit needs to be disconnected, and one more EVAP line needs to be removed from the left top side of the tank. There should be enough flexibility in the line to lower the tank enough to remove it. There is actually a cutout in the body directly above the fuel pump sending unit which might be easier to open and disconnect the fuel pump prior to lowering the tank. I didn’t do this because with the Excellence and the divider I would’ve had to remove a ridiculous amount of the interior to access it. I suspect the standard models are much easier to reach. Also, good information to have if the fuel pump ever dies in the future.
I’m hoping I’m not forgetting anything but at this point the tank should be able to be dropped and slid out. The coolant lines need to be slid over one side of the tank. I removed/installed the tank to the left side of the vehicle. This would have been easier with the exhaust completely removed but I made it work with it just dropped down partially. Then, the sending unit can be removed and placed into the new tank. Again, I would recommend getting a 71L sending unit since it does have the longer rods to hold it to the bottom of the tank. I modified mine with one longer rod, and have had no issues so far, so do at your own risk. There is one fuel line that stays with the sending unit, and this should fit into the moldings in the new tank, just as it did in the old tank.
Installing the new tank is much just the reverse of removing the original. All of the lines that run over the tank should fit into the groves molded in, but some might not fit as perfect as they did in the original tank. The biggest trouble I had with this was the large EVAP line that connects to the top left of the tank. It is much tighter with the new tank, and it is difficult to get it to slot into the grove for it while holding up the tank. Other than that, everything went together pretty easily. The straps felt tight at first but they tightened up against the tank just fine. I did some cleaning and actually broke the wire guard for the HV wires going to the ERAD so a quick zip tie fix, and then worked on installing that. Again, I was very careful with reconnecting these wires. First, I reconnected the large bale style connector, and then the smaller communication cable. The wire guard needs to be slid onto the tangs on the battery at the same the connector is connected. All of the other lines can be reconnected to the tank, and the heat shield should be roughly put back into place, if reusing the original heat shield like I did. If you received a heat shield with your new tank it will have to be removed for installation and reinstalled at this point as well. Finally, the under-tank air shields can be moved back up into place and retained with the new retainers on the bottom of the tank. I used a hole in one of these under-tank shields to retain the heat shield. I used metal zip ties so they wouldn’t melt from the heat or anything.
Once everything is buttoned up on the bottom side the 12v battery can be reconnected and fuel door opened. I added about 5 gallons to the tank before performing any testing. When opening the door and waking up the vehicle the fuel pump primes, so you can kinda hear when it has actually gotten fuel to it. You probably want to do a visual check after filling the tank, and letting the fuel pump prime to check for any leaks. Once verifying all of this I started up the engine and let it run for a while, so I knew it was actually pulling from the tank. I took the vehicle to a gas station and filled up the tank completely, again looking for any leaks. Thankfully I didn’t have any.
I did not change anything about the electronics of the vehicle, and did not receive any CEL or any warnings on the display. The fuel level and miles to empty estimate appeared to be working. The only problem is that since the vehicle thinks it has a 50L tank the miles to empty estimate is not accurate. I was planning on using VDASH to switch the vehicles computer so the miles to empty estimate was more accurate, but I would need to get a CEM pin, and so far I haven’t been bothered to do that.
I am so happy with the swap, and the first full tank in it I got 478 miles. I could barely make it 320 miles on the old tank. This is definitely how they all should have come from the factory, but at least Volvo didn’t change too much so the swap is pretty easy.
I am not sure if I can post pictures on here yet, as this is actually my first post (Longtime lurker first time poster). I didn’t get any super good photos but they might help someone. Let me know and I can try to post some of them.