AT Oil Temp light flashing and engine shudders

Hi there. Looking for some advice on a problem that cropped up after a long trip this weekend.



Coming back down to the SF Bay area from Lake Tahoe, carrying 4 people plus gear, we noticed sporadically throughout the trip that the engine would shudder. The feeling was the same as when the engine is running out of gas, i.e. it’s not getting power smoothly.



Toward the end of the trip, this started happening more often, then the AT Oil Temp light started flashing. At this point the shuddering was happening quite frequently.



We stopped to let it cool down; after we started again it seemed OK for a while, but soon the light started flashing and the shuddering happened again. After another stop to cool down, we drove carefully home and it didn’t happen again.



Seems like there’s a transmission issue. What do you think the problem is, and what should I do about it?



Thanks!

Sorry, should have mentioned it’s a 1998 Subaru Forester with ~204K miles.

Other than getting the car scanned for codes, when if ever has the transmission been serviced?

Aside from any issue related to deteriorated transmission fluid, you might check the final drive gear oil level as this could be caused by a binding ring/pinion gear.
This is NOT the same thing as the transmission fluid even though it’s in the same case.
The dipstick should be on the passenger side, up front, and down low.

Did you check the transmission fluid level??

Yeah, I did check the fluid level, sorry I left that out. AT fluid level is fine, looks a little on the brown side and smells maybe a bit burnt? Unfortunately I don’t know what it smells like normally.

Re service, I don’t know when it was last serviced – I’ll have to look at my receipts.

Re the final drive gear oil level – I haven’t checked (and didn’t know about) that. When I check that, is the only thing I’m looking for the level of the oil? Or is there something else I should check regarding color, consistency, etc. as well?

Thanks for the advice!

Auto trans fluid should be changed every 30K miles. If in doubt, change it (applies to final drive oil too.
You might get lucky and that’s all it needs.

As long as it’s clean looking and near the FULL mark you should be fine there. (knock on wood)

I mention the final drive oil because most people don’t know about that and assume the ATF is it. That’s not the case.

A loss of final drive oil is usually attributed to:

  1. Leakage. Externally (axle shaft seals) or internally (several seals between the final drive compartment and the automatic transmission)
  2. Inadvertently removing the wrong drain plug while changing the engine oil and draining the final drive by mistake as the plugs are located close together. You would be surprised at how common this is and how many transmissions have been wiped due to this.

Lack of final drive oil causes the ring and pinion gear to bind and this may show up as a bucking or lurching and overheated transmission fluid due to the transmission being stressed so much.

Transmission overheating, engine shuddering?? I think the shuddering was the transmission slipping…Which brings you to a fork in the road…Repair it or scrap it…

That doesn’t sound good. Would you recommend even bothering with the fluid change, or should I take it in to the shop and have them look at the transmission now to see what state it’s in?

I’m kind of a cynic and pessimist, buy I would invest $100 or whatever and have it serviced first…They may tell you, after they drop the pan, that you are wasting your time…(chunks in the pan)…

I think I agree with you. Servicing it now wouldn’t be wasted anyway, whether it needs more work or not. I guess the best thing is to take it in now and see what they say. Thanks for the advice.

Should a rebuild be necessary, you need to think about how much value is likely left in the car after the repair and whether that makes sense to you…It’s not an easy choice…Many times, rebuilding these transmissions is cost-prohibitive…

[i] looks a little on the brown side and smells maybe a bit burnt? Unfortunately I don’t know what it smells like normally.

Re service, I don’t know when it was last serviced [/i]

That all sounds rather bad. Sorry

As Caddyman stated in an earlier post, the shuddering is likely to be coming from that self-destructing transmission, rather than from the engine.

Sadly, this sounds like yet another case of a transmission that was rarely–if ever–serviced.
If this was my vehicle, it would have had its trans fluid changed 7 times in its 200k+ miles.
However, I would be willing to bet a fairly substantial sum of money that this transmission has not had anywhere near that amount of servicing.

As Caddyman also implied, the cost of transmission repairs at this point may well exceed the book value of the vehicle. Hopefully the OP will service the trans on his next car more diligently.

I wouldn’t service anything until it’s verified whether the final drive oil level is correct or not.

It appears that you could have a friction element slipping. Usually shudder comes from a slipping torque converter clutch but it could also be one of the overdrive clutches. You might try driving with the overdrive off and see if the shudder still exists. The engine will be at a higher RPM but it should not be too high. If the transmission still shudders, lightly touch the brake pedal (not enough to actually engage the brakes but enough to get the tail lights to come on). The torque converter clutch should disengage. If the shudder stops you might get by with just changing the TC.

Since the AT Oil Temp light is coming ‘on’, the fluid has been toasted. The fact that the fluid is brown and smells burnt indicates that things have gotten really hot inside the transmission. But with the mileage on this car it is probably that a total rebuild might be necessary. You might run this car by a transmission shop to see if the technician can narrow down what is actually slipping. As ok4450 recommended have the transmission control computer scanned for codes–the computer will have a wealth of information.

BTW, when the AT Oil Temp light came ‘on’, did the transmission shift harshly out of overdrive and the shuddering stop? Were the subsequent shifts harsh and overdrive locked out until the car was turned ‘off’ and rested?

Let us know what you find and what you decide to do.

Thanks for all of your suggestions. A few updates on my case for those of you still interested.

Last transmission service was done at 150K, including a full flush. Nothing since then, so it hasn’t seen as much service as it probably should have, but not none.

Front differential oil was very low. Refilled, and it seems to be behaving a little better but I only took it up and down the road a couple miles. Couldn’t check the rear diff for lack of a square driver to fit.

I’m taking it in to a local transmission shop to have it looked at tomorrow.