kramer wrote:The transmission cooler inside the rad is a supplementary piece, and I suspect it has more to do with bringing the temperature UP in winter rather than DOWN in the summer.

You know the more I think about this, Im not so sure how true that is. The thermostat in the cooling system isnt going to open until the engine reaches operating temperature. So the coolant in the radiator will remain ice cold until that happens. And being that the engine is up to temp, I would think the trans shouldnt be far behind. Guess Ill know if I get a lot of hard shifts this winter when starting off.

Budrbean wrote:

kramer wrote:The transmission cooler inside the rad is a supplementary piece, and I suspect it has more to do with bringing the temperature UP in winter rather than DOWN in the summer.

You know the more I think about this, Im not so sure how true that is. The thermostat in the cooling system isnt going to open until the engine reaches operating temperature. So the coolant in the radiator will remain ice cold until that happens. And being that the engine is up to temp, I would think the trans shouldnt be far behind. Guess Ill know if I get a lot of hard shifts this winter when starting off.

Good point Budr.

I live in the cold north (winnipeg) and it was -30C many times during the long winter. I noticed that the transmission is harsher shifting when cold, but not moreso with the bypass.

In any case, I give the truck an extra couple minutes to warm up when its cold, and usually plug in the block heater. Works out cuz it takes a while to load the kiddles.



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I've added a transmission fluid temp gauge.

cruising on freeway at night, 55F weather, I get 125F
cruising on freeway at day, 90F weather, I get 165F
towing on freeway at day, 90F weather, I get 165-190F
towing in traffic, 90F weather, I get 210-250F.

I also added an extra fan on the trans fluid cooler, it brings temp down another 5-15F depending on speed.

so the trans cooler inside radiator is to bring temp up when cold, and bring it down when hot. but since radiator operated in ~200F for emission reason, I think that's too hot for trans fluid. bypass is a good idea, imo.

Budrbean wrote:

kramer wrote:The transmission cooler inside the rad is a supplementary piece, and I suspect it has more to do with bringing the temperature UP in winter rather than DOWN in the summer.

You know the more I think about this, Im not so sure how true that is. The thermostat in the cooling system isnt going to open until the engine reaches operating temperature. So the coolant in the radiator will remain ice cold until that happens. And being that the engine is up to temp, I would think the trans shouldnt be far behind. Guess Ill know if I get a lot of hard shifts this winter when starting off.

In winter time the engine will heat up way waaaay sooner than the transmission, especially considering that most people will idle their car for a few minutes (or more) to warm it up prior to setting off. Your transmission on the other hand doesn't benefit from an idling engine... it only warms up once you actually start driving.

engine coolant (Rad temp) should be warmer than what you would want your trans fluid temp (260 vs 180'ish) ?

If your engine is running at 260F you've got problems

bellwilliam wrote:I've added a transmission fluid temp gauge.

cruising on freeway at night, 55F weather, I get 125F
cruising on freeway at day, 90F weather, I get 165F
towing on freeway at day, 90F weather, I get 165-190F
towing in traffic, 90F weather, I get 210-250F.

I also added an extra fan on the trans fluid cooler, it brings temp down another 5-15F depending on speed.

so the trans cooler inside radiator is to bring temp up when cold, and bring it down when hot. but since radiator operated in ~200F for emission reason, I think that's too hot for trans fluid. bypass is a good idea, imo.

Thats about the temps I get. Not sure on towing because I havent towed yet, but regular stop and go traffic it creeps to about 210.

I also have the same thinking on the radiator heating the fluid.

kramer wrote:

Budrbean wrote:

kramer wrote:The transmission cooler inside the rad is a supplementary piece, and I suspect it has more to do with bringing the temperature UP in winter rather than DOWN in the summer.

You know the more I think about this, Im not so sure how true that is. The thermostat in the cooling system isnt going to open until the engine reaches operating temperature. So the coolant in the radiator will remain ice cold until that happens. And being that the engine is up to temp, I would think the trans shouldnt be far behind. Guess Ill know if I get a lot of hard shifts this winter when starting off.

In winter time the engine will heat up way waaaay sooner than the transmission, especially considering that most people will idle their car for a few minutes (or more) to warm it up prior to setting off. Your transmission on the other hand doesn't benefit from an idling engine... it only warms up once you actually start driving.

I live in the south and the 20's is usually the lowest I see. I usually crank and go, so thats more of what I was referring to

kramer wrote:If your engine is running at 260F you've got problems

Ok so Im sure his engine isnt running that hot, but he still has the right idea. Lets say operating temp of the engine gets the coolant to 200-210, its gonna pass that heat right along. My external cooler alone in most driving keeps my fluid under 175, which according to manufacturers for ATF, dramatically increases the life of the fluid. So yeah, Im in agreement that even if there were no radiator issue, maybe the bypass isnt so bad of an idea anyway.

You have to factor in that the coolant at the bottom of the radiator is going to be cooler than the coolant coming in from the engine at the top. What the temp is at the bottom after the coolant has gone through the radiator I couldn't say but I still think the radiator trans cooler has some cooling effect in hot weather/extreme conditions.

pawjr74 wrote:You have to factor in that the coolant at the bottom of the radiator is going to be cooler than the coolant coming in from the engine at the top. What the temp is at the bottom after the coolant has gone through the radiator I couldn't say but I still think the radiator trans cooler has some cooling effect in hot weather/extreme conditions.

ha typo, sorry. But that is a thought ^ since the bottom of the rad should be cooler, I'm still stickin with my bypass though, my fluid is still nice and clear and red after about 4 months. I gotta get around to adding a temp gauge

Update on my Path:

I found a mechanic willing to do payments. The cost was 1900.00. He first confirmed the coolant in the oil. He mentioned that he gets a few of these a month. Not just Nissans, but that he has done a few Paths before as well.

Anyways, he rebuilt the tranny and replaced the converter and the car has been running fine for almost a month. He also suggested bypassing the cooler and in the future get an external one if possible. I just had mine bypassed for now.

For those of you that have not done the bypass, DO IT.

djbit wrote:Update on my Path:

I found a mechanic willing to do payments. The cost was 1900.00. He first confirmed the coolant in the oil. He mentioned that he gets a few of these a month. Not just Nissans, but that he has done a few Paths before as well.

Anyways, he rebuilt the tranny and replaced the converter and the car has been running fine for almost a month. He also suggested bypassing the cooler and in the future get an external one if possible. I just had mine bypassed for now.

For those of you that have not done the bypass, DO IT.

thats a very good price

So far there is no transmission oil in the coolant on my 2006 PF, 4x4, mfg in 10/2005, with the original Nissan Calsonic radiator, 71K miles, tow pkg. But after reading scores of horror stories, I’m running scared. Also other car brands have been dealing with this but to a lesser extent, by what I read. And I realize that each brand tends to have their share of inherent weaknesses, such as the 98 Tahoe I traded last winter for this 06 PF. Three times the intake manifold gasket was replaced out of warranty, one fuel pump, EGR electronic valve, plus other “normal” repairs.

So my thoughts are to replace the radiator now before problems arise, do you all agree with this preventative strategy? If so, any brand preferences? I do tow, hence need the cooling capacity.

Thanks,

CPLTECH wrote:So far there is no transmission oil in the coolant on my 2006 PF, 4x4, mfg in 10/2005, with the original Nissan Calsonic radiator, 71K miles, tow pkg.
So my thoughts are to replace the radiator now before problems arise, do you all agree with this preventative strategy? If so, any brand preferences? I do tow, hence need the cooling capacity.

Thanks,

this thread* is long, but very comprehensive regarding this problem
long term fix - difficult to recommend
but in the short term, transmission oil in the coolant is sometimes difficult to detect
better to check for coolant in the trans oil
sometimes this is tough to see on the dipstick
all depends on how serious the contamination is, if any
my recommendation, at least for now, is to do the by-pass, and while doing so, drain some trans oil into a container and take a good look at it
that will give you the opportunity to determine if a problem exists, and be doing a preventative measure to avoid it until you decide on the proper long-term solution
i too would like to replace the radiator, or add an additional cooler and/or fan, but have not decided which way to go
but, at least there's no worry about transmission failure due to coolant contamination until then

* http://www.thenissanpath.com/viewtopic. ... oil+cooler