75w85 vs 80w90 manual gearbox oil

Welcome to 2CarPros.

You are correct. The fluid that was installed is heaver than the manufacturer's recommendation, and that can be what is causing what is happening.

I would recommend taking it back and have them install the correct weight of oil. Please keep in mind, the manufacturer takes into consideration different temps when engineering the vehicle. They know best.

I attached a picture which indicates the recommended weight and capacity. Also, if you want to do it yourself, here are the directions. The remaining pictures correlate with these directions.

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PROCEDURES
Service Adjustment Procedure

Transaxle Gear Oil Level

Replacement
1. With the vehicle parked on a level surface, remove the drain plug.
2. Drain the transaxle oil after loosening the drain plug(A).

Picture 2

3. Install the drain plug with new washer.

Drain plug tightening torque:
60-80 Nm (600-800 kg-cm, 43-58 lb-ft)

4. Add new oil through the file plug hole and, fill it just below the plug opening.

Standard oil SAE 75W/85, API GL-4
Oil capacity:1.9 liter (2.0 US qt, 1.67 lmp qt)

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Let me know if you have other questions or need help.

Take care,
Joe

Hi,

The main difference in these oils is the fact that the 75w-85 is rated to go to -40 degrees. The other is only -20.

The difference between the 85 and 90 is the 90 is a little bit thicker that the 85. This may be where your shifting issue is coming from. I wouldn't think so because once the fluid is hot it should be fine but if you didn't have it before and now you do, the thicker fluid could cause it.

I wouldn't change it again unless you want to be safe and stick to what the OEM says to use. I always do just because they designed and engineered the product using that fluid.

Hopefully this helps. Please let me know if you have any questions. Thanks

I agree with what Kenny said. I too feel it is the cause of the shifting differences you are experiencing. If it was me, I would ask that they (the dealer) replace it with the correct weight at no charge.

Let us know if you have other questions.

Take care,
Joe

Both fluids can operate in this temp range but that means you are going to have thicker/heavier fluid when you don't need it. The recommended oil is well within that range so I would stick with that.

Keep in mind, the dealer most likely used that fluid because that is what they had. They could have gotten the correct fluid but they probably buy the other in bulk and use it whenever they can because it gives them greater profit on the same job due to them buying it in bulk.

It says right on the document that this is for heavy duty application. Your gear box is not under heavy duty use. This is an industry term that is meant for heavy hauling like work trucks, police cars, mail carrier vehicles. These types of vehicles run all day and are run hard. Passenger cars do not fall under this category.

I would have it changed if for no other reason that it was not designed for it. Not to mention you are experiencing an issue after they did it.