Replacing Trans & Diff Fluid, Hot vs Cold
 

I am going to change my manual transmission and rear differential fluid soon. Should I let the car sit overnight to ensure all the crap is at the bottom when it drains out? Or do it after the car has been driven for a few miles to warm up the fluid and make it flow better? I've been reading all the treads on changing out your trans fluid, but didn't seem to get a general consensus from how everybody has been doing it.

I've always changed oil and fluids when warm so they flow better, but I am far from an expert. I'd be interested to see what a real mechanic has to say about this.

Do it warm.

I don't think it much matters.

humfrz

Be careful not to do it immediately after a drive as the oil can be very hot. If your car has been sitting overnight just take it for a short 5-10 min drive, then go back and have a cup of tea before you start the job. It should cool down nicely but just warm enough for the oil to flow better.

Realistically I don't think it matters even if you did it cold....the differences will be negligible.

Thanks for feedback. I'll do it when it is warm.

Drain oil while warm as it flows better. Wear gloves and safety goggles just to protect yourself.

warm is easiest, also helps to warm up the new fluid before you pump it in makes life easier. i use a construction spot light to warm up the bottles before i put them in

Service experts all agree that changing splash fluid reservoirs should be done before the particulate matter has time to settle.

Cold or hot is immaterial, but if drained right after running, this is mostly hot. The fluid will drain and fill quicker if hot, but that is simply a convenience detail.

Otherwise, there is the possibility that some of the contaminants will have "settled" somewhere in the diff that won't easily drain off. Having done this just last night on my Impreza at 10,000 miles, there may be A LOT of contaminants in this differential.

Shawn



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