Bucking/surging engine on cold right turn, acceleration

[tekman78]

In the spring I had 120k fluids done. Had the CVT/transfer/diff drained and filled. Not flushed. When I left the shop and I'd taken my first right, I'd felt this engine bucking/surging I'd never felt before as I was going through the turn and accelerating. Lasted only a second and I hadn't felt it again. Until recently once it got cold.

Now, I can reproduce it on a cold start pretty easily with the temps in the 30's. Once the car is warm I never feel it. The whole engine bounces around like crazy as I'm hitting the gas going through the turn. Like something is slipping like crazy or not getting the appropriate fluid.

I know they didn't use OEM fluids in the spring. I had the same service done at my dealer at 60k, but with OEM fluids. I understand the appropriate weights were used both times.

Anyone have any advice on what could be happening? Doesn't seem to happen with a left turn. Seems like one of the new fluids is either a bit heavier or maybe wasn't filled properly. For those that know more about the layout of the vehicle mechanically, especially the trans and how the fluid rests/flows, what would make sense for this surging/bucking that I feel?

I'm taking it in on Tuesday but wanted some thoughts on it before just letting them they are start throwing fixes at it.

[silverton]

the older cars would fuel starve on right turns under 1/4 tank, you shouldn't have that issue though

[ammcinnis]

On 1/15/2023 at 3:17 PM, tekman78 said:

In the spring I had 120k fluids done ... I know they didn't use OEM fluids ... I understand the appropriate weights were used ...

That would be the primary suspect, IMO. The differential fluids aren't critical, and can be sourced from among many brands, as long as they meet Subaru's technical specifications, but the CVT fluid is another matter. Subaru is the only source for CVT fluid guaranteed to be correct for your Legacy. Subaru uses several different fluids, unique to each CVT model (TR580 or TR690) and production variant ... i.e. different model years may require different fluids, even within the same CVT model. Especially risky are the "One Fluid for All CVTs" products, even from the boutique brands.

My recommendation is to perform at least one CVT fluid drain-and-fill using the correct Subaru-branded CVT fluid. (I believe that the dark green Subaru CVTF-II is correct for your MY 2015 TR580.) This may help your problem, although there is a remote possibility that your CVT may never fully recover.

 

Edit: FWIW, check that your engine oil isn't overfilled. According to Subaru, even a seemingly-minor overfill can cause symptoms of bucking and surging. The dipstick is a cheap and easy way to eliminate that possibility. 

 

[tekman78]

15 hours ago, ammcinnis said:

That would be the primary suspect, IMO. The differential fluids aren't critical, and can be sourced from among many brands, as long as they meet Subaru's technical specifications, but the CVT fluid is another matter. Subaru is the only source for CVT fluid guaranteed to be correct for your Legacy. Subaru uses several different fluids, unique to each CVT model (TR580 or TR690) and production variant ... i.e. different model years may require different fluids, even within the same CVT model. Especially risky are the "One Fluid for All CVTs" products, even from the boutique brands.

My recommendation is to perform at least one CVT fluid drain-and-fill using the correct Subaru-branded CVT fluid. (I believe that the dark green Subaru CVTF-II is correct for your MY 2015 TR580.) This may help your problem, although there is a remote possibility that your CVT may never fully recover.

 

Edit: FWIW, check that your engine oil isn't overfilled. According to Subaru, even a seemingly-minor overfill can cause symptoms of bucking and surging. The dipstick is a cheap and easy way to eliminate that possibility. 

 

Really appreciated on these details. Exactly what I was hoping to hear. If it's not low, I'm having them flush/fill w OEM and see how it goes.