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Old 11-30-2018, 09:10 AM   #1
JessJ82
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Join Date: Oct 2006
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Location: western mass
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2015 impreza WRX
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Default front diff fluid level? Hot vs cold.

I may be a little OCD about this, but I just did a fluid change on my 15 wrx, in the front and rear diff, and when I check the level in the front when its cold, its exactly at the full line, and when i check it hot, its over the line. Should I be concerned about having too much??

I didn't have access to a 2 post lift, so i literally waited a half hr lifting each corner of the car making sure i took out as much of the gear oil out of the front diff, before putting exactly 3.5 quarts in, and sure enough, i had to take almost a half quart back out, after the first check of the levels. I took it for a quick drive and rechecked, and it was right on the money. The following day, drove it to and from work, rechecked when i got home (warm), and it was too high . Rechecked in the morning and on the money with the full line.

I know I might be OCD, but some reassurance that I am good would be nice, don't want to keep uncracking the crush gasket.
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Old 11-30-2018, 09:21 AM   #2
jasonwrx86
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2018 WRX Limited
CWP

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Fluid expands of course. You should always gauge when the fluid is cool.
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Old 11-30-2018, 10:45 AM   #3
Charlie-III
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Silver Sleeper BK, 5MT

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Quote:
Originally Posted by jasonwrx86 View Post
Fluid expands of course. You should always gauge when the fluid is cool.
Agreed, unless the FSM states something else like the CVT's want to be checked at a certain narrow warm range, or standard AT's should be at normal temp.
MT's and diffs are normally checked at "cold".
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Old 12-01-2018, 06:22 PM   #4
SoonTM
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After changing my front diff fluid I checked the level and it was ever so slightly above full (which is strange because I put less in than it required). I figured it didn't matter and so far nothing bad has happened.

I would assume it is supposed to be checked cold, but if it really worries you maybe keep it in the middle or closer to the "low" mark so it has room to expand when it gets hot. As long as it's kept above "low" it should have enough oil.
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Old 12-01-2018, 06:42 PM   #5
sogah87
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Crystal White Pearl

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SoonTM, there will always be residual in the transmission after changing the fluid. Filling it within OEM spec will often times cause it to appear just over full. Some prefer to let it drain for an extended period to avoid this, mostly for OCD reasons. Unless its extremely full, then it likely will not be an issue.
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Old 12-01-2018, 11:51 PM   #6
SoonTM
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Yeah I figured it was residual gear oil. It just retained a lot more of the old oil than I thought it would. I put probably 0.2 to 0.3 quarts less than it called for (1.3 quarts) and it still went over.

And just to clarify, my car has an automatic transmission. The front diff oil is separate from the transmission fluid. I would probably be a bit more concerned if the transmission was affected but I figure that the diff won't care much if it's slightly over.
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