I have a 2002 Nissan Maxima QX SE Plus 3.0 Auto (A33 Series - and please note this is a UK car, not american, in case it makes a difference) that is currently experiencing cooling problems. The garage found the radiator to be blocked and have a new rad on order.
At the bottom of the rad, and integral to it, is an oil cooler pipe for the automatic transmission. When the mechanic disconnected the pipes to lift out the rad he expected a certain amount of oil to come out but they were dry - and I do mean bone dry. No oil has been anywhere near those pipes for a long time, he reckoned. He said that he's come across situations where the oil cooler pipe in the rad has been leaking so the pipes from the auto box have just been joined together effectively bypassing the cooler pipe, but that wasn't the case here. The pipe in the rad has not been blocked in any way as he could/can blow air through it (and no oil came out then either).
So to my question:
Is there some sort of valve within the automatic transmission that only opens when the fluid gets hot enough to need cooling down, and in this case it's just never been hot enough to need diverting to the cooler, or should there be a permanent flow of fluid from the gearbox to the cooler and back again?
I should say that I've had the car for two years, it drives like a dream and I've never noticed a problem with the auto box at all, apart from over the last 6 months I've noticed downshifts becoming _slightly_ jerkier and when going from neutral to drive there's a _slightly_ harsher jerk than there used to be, but these really are very small changes from normal. ATF fluid level is normal and no colour change.
This really would not have come to light if it had not been necessary to remove the radiator but, now that it has, is it a problem?
TIA