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Pressure Gauge on Transmission cooler line

akxj01

NAXJA Forum User
Location
anchorage
Has anyone put an oil pressure gauge on their trans cooler lines?

What PSI should I get on the cooler lines? (I am assuming it would be pretty low)

I thought I may do it in order to be able to tell if there is a leak in the system or out of fluid completely.

Thanks.
 
i dont think it would be all that handy, your first indication of a major leak will be the smell of hot tranny fluid, followed by poor shifting and driving. a loss of 2 quarts is noticeable.
 
i dont think it would be all that handy, your first indication of a major leak will be the smell of hot tranny fluid, followed by poor shifting and driving. a loss of 2 quarts is noticeable.
i agree, if its leaking you will know immediatley. more beneficial would be a temp guage.
 
everyone seems to think you would realize pressure loss, but a friend just lost an AW4 due to loss of fluid, and then being run dry. and i have ran mine dry as well! both due to cooler lines.
you cant allways generalize stuff like this. he obviously didnt see or smell anything till it was too late...

if nobody else is... i am interested, let ME know if you take this anywhere
 
I would think that you'd kill it with slow, gradual fluid loss and not checking the dipstick. Sudden loss as you'd see if a line failed should become fairly obvious right away. I think the pressure would be quite low and I don't think you'd see any reduction in pressure until the pump started sucking air.
 
Pressure in the cooler lines is residual at most - it's just enough to circulate things. If you want to tap into the cooler lines for anything diagnostic, I would think that a flow rate meter would be more informative (flow and pressure are largely independent - and you'd notice a fall-off in flow there long before the pressure went stupid.)

There's a test port in the side of the case - up above the NSS, I believe - that is used for diagnostic pressure information. That's useful, but you'll need to make sure that your pressure gage kit can handle up to somewhere around 300-350psig, and I'd not want to leave something like that installed as a mechanical gage with a line that long (Heaven help you if it blew out!)
 
I had one break on me and when I had the new one made at the tranny shop he said there was 60lbs pressure going through them.

That much? I'm surprised. By the time it's going to the cooler, the fluid has done its work - and the pressure should have fallen off significantly (akin to the voltage drop across an electrical component. The item doing the flowing is different, but there's not a lot of difference in principle between electronics and fluid power...)
 
its a lot easier then you think to lose fluid, especially on 2nd hand jeeps with quick disconnects waiting to fail. how are you gonna notice smoke coming out of the jeep if your leaking smoke outta your passenger compartment 2/3rds of the time?

has anyone thought about using something like one of those moroso oil pressure switches that turns on warning lights if you lose oil pressure? but for the tranny
http://www.moroso.com/catalog/categorydisplay.asp?catcode=13024
 
has anyone thought about using something like one of those moroso oil pressure switches that turns on warning lights if you lose oil pressure? but for the tranny
http://www.moroso.com/catalog/categorydisplay.asp?catcode=13024

this seems like a geat idea, although it depends what the PSI is in the cooler lines ( I was guessing around 10 psi)......as the info on this product states on the website, it can be dialed in to turn on between 15 and 50 psi

also, i have the B&M trans temp gauge, just thought I would add smething to indicate low pressure or flow

5-90...this flow indicator you referred to sounds interesting...any other info on that?
 
this seems like a geat idea, although it depends what the PSI is in the cooler lines ( I was guessing around 10 psi)......as the info on this product states on the website, it can be dialed in to turn on between 15 and 50 psi

also, i have the B&M trans temp gauge, just thought I would add smething to indicate low pressure or flow

5-90...this flow indicator you referred to sounds interesting...any other info on that?

Liken a hydraulic "circuit" to an electrical one.

Volts = Pressure
Current = Flow

Thus, a "flow gage" is little more than the hydraulic analogue to an Ammeter - all it will tell you is how much fluid flows past a certain point. No pressure reading (probably don't need one there anyhow,) no temperature - just how much fluid. If it drops off significantly, or falls "out of pattern" (I'm sure the flow rate would be different for different gear ranges,) stop and find out why.

If you want a useful pressure reading, tap a double-sealed pressure transducer into the test port on the case and run that to an IP gage. Memorise - or post somewhere convenient - the pressure test table from the service manual.

If all you want to do is make sure enough fluid is going through the system, then a flow meter should be enough - and tapping that into the cooler line is easiest (and should actually give the most accurate reading anyhow. The pump picks up fluid, runs it through the system, and it gets heated up. It has to be cooled off, yah?)

If you want a temperature reading, I'd actually get two - one coming out of the case (the line going to the cooler) and one coming into the case (to gage the efficiency of the cooler.) These can be done with a single gage, two sensors, and a switch to go back and forth, or you can find "dual temperature" gages where you have two meters in a single case - if you can't find them in speed shop catalogues, you can find them in aircraft kitbuilder's/experimenter's catalogues. Check with Wick's Aircraft Supply or Aircraft Spruce & Supply for information (note - avionics are never cheap - but the damned things are as reliable as bricks.)
 
That much? I'm surprised. By the time it's going to the cooler, the fluid has done its work - and the pressure should have fallen off significantly (akin to the voltage drop across an electrical component. The item doing the flowing is different, but there's not a lot of difference in principle between electronics and fluid power...)

I was surprised as well but he was pretty confident in his answer. I always defer to the pro's in these situations!
 
I was surprised as well but he was pretty confident in his answer. I always defer to the pro's in these situations!

I'm not saying he's wrong - just that I'm surprised. My experience (with industrial hydraulics, to be sure...) has shown that you'd have ~10-15psig - tops - left over after the fluid has done its work, if the pump is sized correctly to the rest of the system. If a pressure line gets a pinhole, it's like a water knife and can (and do!) cut things in some systems. If a return line gets a pinhole, so what? Most of the time, the leak will run down the length of the line to the lowest point and then drip off of the hose.

But, that's industrial hydraulics, and I'm sure that automotive transmissions are different (even from automotive fluid power, like on medium duty trucks. Dump trucks, tilt beds - all of those systems are different from transmissions.)
 
i think most of us arent interested in numbers.... just kinda a go/no go gauge, something that will save an aw4 should a line failure happen. will a temp gauge show anything in this situation?
 
Liken a hydraulic "circuit" to an electrical one.

Volts = Pressure
Current = Flow

Thus, a "flow gage" is little more than the hydraulic analogue to an Ammeter - all it will tell you is how much fluid flows past a certain point. No pressure reading (probably don't need one there anyhow,) no temperature - just how much fluid. If it drops off significantly, or falls "out of pattern" (I'm sure the flow rate would be different for different gear ranges,) stop and find out why.

If you want a useful pressure reading, tap a double-sealed pressure transducer into the test port on the case and run that to an IP gage. Memorise - or post somewhere convenient - the pressure test table from the service manual.

If all you want to do is make sure enough fluid is going through the system, then a flow meter should be enough - and tapping that into the cooler line is easiest (and should actually give the most accurate reading anyhow. The pump picks up fluid, runs it through the system, and it gets heated up. It has to be cooled off, yah?)

If you want a temperature reading, I'd actually get two - one coming out of the case (the line going to the cooler) and one coming into the case (to gage the efficiency of the cooler.) These can be done with a single gage, two sensors, and a switch to go back and forth, or you can find "dual temperature" gages where you have two meters in a single case - if you can't find them in speed shop catalogues, you can find them in aircraft kitbuilder's/experimenter's catalogues. Check with Wick's Aircraft Supply or Aircraft Spruce & Supply for information (note - avionics are never cheap - but the damned things are as reliable as bricks.)

5-90 thank you very much.

flow meter is the way. i just want to make sure i have fluid going through the system. it would be even better to get a flow meter designed with an indicator light to come on when flow falls below a designated rate.

i'll start searching for flow meters.....although do you have any you can recommend?

also, i'll get a 2nd B&M sender to put on the return trans cooler line and combine it with a double throw switch and the B&M trans gauge/ sender i have on the supply/ pressure line. (or maybe just get another B&M gauge with sender....the sender is only like $14, where the gauge and sender is around $50)

all good info from you all thanks....and any more is certainly appreciated

there's few things like being stranded is the middle of nowhere (n)...any thing within reason to prevent breakdowns is worth doing.
 
5-90 thank you very much.

flow meter is the way. i just want to make sure i have fluid going through the system. it would be even better to get a flow meter designed with an indicator light to come on when flow falls below a designated rate.

i'll start searching for flow meters.....although do you have any you can recommend?

also, i'll get a 2nd B&M sender to put on the return trans cooler line and combine it with a double throw switch and the B&M trans gauge/ sender i have on the supply/ pressure line. (or maybe just get another B&M gauge with sender....the sender is only like $14, where the gauge and sender is around $50)

all good info from you all thanks....and any more is certainly appreciated

there's few things like being stranded is the middle of nowhere (n)...any thing within reason to prevent breakdowns is worth doing.

Most of the flowmeters I've been looking at of late have been for gases (mainly oxygen,) so I can't really recomment one over the other. Which are you looking at? I'd like to see them myself.

And, I've no idea what would be a "nominal" flow rate - I don't have an AW4 pump to take to bits anywhere handy, so I can't figure flow based on that (or restrictions in the system, or ...) So, you'd have to work from experimentation to see what would be a "wrong" reading somewhere above zero.

But, a flow meter would tell you there is fluid flow through the system - that's what it's designed to do!
 
Most of the flowmeters I've been looking at of late have been for gases (mainly oxygen,) so I can't really recomment one over the other. Which are you looking at? I'd like to see them myself.

And, I've no idea what would be a "nominal" flow rate - I don't have an AW4 pump to take to bits anywhere handy, so I can't figure flow based on that (or restrictions in the system, or ...) So, you'd have to work from experimentation to see what would be a "wrong" reading somewhere above zero.

But, a flow meter would tell you there is fluid flow through the system - that's what it's designed to do!

as far as flow rate, i believe the FSM details it. i'll have to look to make sure but i thought i once read that if you pull the return line out of the back of the AW4 and start the jeep, if i remember correctly, about 1 quart should come out in 30 seconds. i;ll have to double check though.

so, if 1 quart per 30 seconds is correct, i could do that test and if that rate is what i get, then whatever the flow rate is on the flow meter should be desinated the standard.

if 1 quart per 30 seconds is correct (again, i need to double check with the fsm) i would guess the psi to be very low like you mentioned earlier.
 
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