Simple question about checking tranny fluid - Pirate4x4.Com : 4x4 and Off-Road Forum

Dignan · 08-12-2004, 08:22 AM

I recently changed the transmission fluid in my runner and when I checked the fluid level I realized the hot mark on the stick is ABOVE the cold mark.

No, this is not the first time I've checked the fluid, but I'd never really given it much thought. So here goes....if the pan is acting as a collection area for the sump, then logically the fluid in the pan would read higher when the engine has cooled and the fluid has slowly collected back into the pan. Right? Obviously not, but I would like to know why.

Also, which reading is more accurate in your opinion. I've always thought a hot reading was better but now I'm not sure.

f f f-lame away.

Bullseye · 08-12-2004, 12:47 PM

Automatic transmission fluid levels are usually checked when the engine is warmed up and after the vehicle has been run a short distance. Most manufacturers recommend some sort of "ritual" (e.g. shift through all gears, then place transmission in either park or neutral) so that the fluid is evenly distributed within the transmission. The theory is that, with fluid distributed throughout the transmission and with the system warmed up, there should be enough reserve supply in the "sump" to supply the system with fluid throughout its operating range. Oil expands in volume when heated. Filling your transmission to the "full" mark on the dip stick when its cold would result in an overfill conditon when it's hot.
Hope that helps

Dignan · 08-13-2004, 04:02 AM

yeah, thanks. I've read several more places that indicate oil expansion is the only reason for the different reading. I guess I was thinking that a cool engine would still have more fluid collected in the pan....but, when I thought about how quickly you can remove 4 quarts with the oil cooler line disconnected and the vehicle idling...that pump is emptying the pan quick.

thanks again.

08-12-2004, 08:22 AM	#1 (permalink)
Dignan Registered User Join Date: Jul 2004 Member # 33412 Posts: 0	Simple question about checking tranny fluid I recently changed the transmission fluid in my runner and when I checked the fluid level I realized the hot mark on the stick is ABOVE the cold mark. No, this is not the first time I've checked the fluid, but I'd never really given it much thought. So here goes....if the pan is acting as a collection area for the sump, then logically the fluid in the pan would read higher when the engine has cooled and the fluid has slowly collected back into the pan. Right? Obviously not, but I would like to know why. Also, which reading is more accurate in your opinion. I've always thought a hot reading was better but now I'm not sure. f f f-lame away.

08-12-2004, 12:47 PM	#2 (permalink)
Bullseye Registered User Join Date: May 2004 Member # 30214 Location: Sierra Foothills Posts: 44	Automatic transmission fluid levels are usually checked when the engine is warmed up and after the vehicle has been run a short distance. Most manufacturers recommend some sort of "ritual" (e.g. shift through all gears, then place transmission in either park or neutral) so that the fluid is evenly distributed within the transmission. The theory is that, with fluid distributed throughout the transmission and with the system warmed up, there should be enough reserve supply in the "sump" to supply the system with fluid throughout its operating range. Oil expands in volume when heated. Filling your transmission to the "full" mark on the dip stick when its cold would result in an overfill conditon when it's hot. Hope that helps __________________ Many people create mountains in their lives, only a few people actually climb them. ----------------------------------------------- The child is not the caretaker for the parent’s emotions, and should never be made to feel responsible for the parent’s anger.

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08-13-2004, 04:02 AM	#3 (permalink)
Dignan Registered User Join Date: Jul 2004 Member # 33412 Posts: 0	yeah, thanks. I've read several more places that indicate oil expansion is the only reason for the different reading. I guess I was thinking that a cool engine would still have more fluid collected in the pan....but, when I thought about how quickly you can remove 4 quarts with the oil cooler line disconnected and the vehicle idling...that pump is emptying the pan quick. thanks again.