2015 3.5 N/A PTU Temp Sensor Mod question

[15ExpLimited]

Hi all, I have a 2015 Explorer Limited 3.5 N/A without a drain plug on the PTU, and I regularly take the car off-road, climbing muddy steep hills and moguls and getting 1-2 wheels off the ground, I know the PTU's are a weak spot on these explorers; and Ive already changed the fluid once and added the tow package underbody air duct as this is a factory non tow package vehicle (also tried doing the vent extension mod and then dismally found out TT ecoboosts have a vent and N/A's use a one way valve pressed directly into the case of the PTU), but im still paranoid about the PTU, does anyone know the thread pitch of the PTU's fill port? would it be possible to thread an aftermarket temp sensor in place of the old fill port and maybe wire up a tiny gauge on the interior?

 

[Steve8316]

Go to a local parts store, and ask to look at a direct-replacement sensor so you can measure the threads. Do you know your fill plug's thread size?

Do you know what temperature is dangerous to the PTU, or what to do if its temperature approaches that? If not - there's no point having a gauge.

 

[15ExpLimited]

Go to a local parts store, and ask to look at a direct-replacement sensor so you can measure the threads. Do you know your fill plug's thread size?

Do you know what temperature is dangerous to the PTU, or what to do if its temperature approaches that? If not - there's no point having a gauge.

No I don’t I was hoping someone on here might have the information on hand, I already tried getting the thread type from searching up the plug on fords part website and rockauto but no such luck.

 

[Steve8316]

If you don't know what temperature to watch for, or what to do at that temp, then the gauge would be worthless. And if you don't know your plug's threads, knowing the sender's threads would be useless.

 

[15ExpLimited]

If you don't know what temperature to watch for, or what to do at that temp, then the gauge would be worthless. And if you don't know your plug's threads, knowing the sender's threads would be useless.

If you don't know what temperature to watch for, or what to do at that temp, then the gauge would be worthless. And if you don't know your plug's threads, knowing the sender's threads would be useless.

I’m realizing that the mobile version of this website is not the best way to interact or use this, there was an undismissable TEMU ad in the way and I missed the entire bottom half of that post and was only able to read it up until the “Do you know your fill plug's thread size?” which for a fact no I don’t, as for everything else yes I know the that the flashpoint of 75W-140 is 375~ F and I know that 250-275F is approaching the limit for a rear diff, I know that just by nature the physical design of the PTU with no cooling or directional fins like on a CD2 PTU, space constraints, and how little fluid these hold they will get be on the hotter end of the scale by nature, and while I don’t know a specific magical number of what the nominal temp these PTU’s sit at using information from other forums with people owning Foci RS, Taurus SHO PP, and PIU Tauri’ and Explorers I’ve seen how hot they can get during on road heavy use, mishimoto has recorded the front PTU reaching as high as 300F WITH factory liquid cooling on a Focus RS, so I know without a doubt at low speed, hot ambient temperatures with 1-2 wheels regularly going in the air my PTU is inevitably getting hot, I’d just like to install a sensor to know HOW hot my PTU is in the moment so I can preemptively start backing off or park it instead of waiting for it to get hot enough to puke gear out out of its one way valve and realizing that it’s too hot and already cooked. this website is making me look more and more foolish and I’m giving up more and more on the mobile version. My iPhone 15 is lagging too much.

 

[15ExpLimited]

If you don't know what temperature to watch for, or what to do at that temp, then the gauge would be worthless. And if you don't know your plug's threads, knowing the sender's threads would be useless.

So with that being said sorry if my comment seemed sassy or excessive but yes I know what temps to watch and look out for in regards of of the PTU, I’m just asking if anyone knew or had the thread type on hand for the fill port of a 3.5 N/A PTU so I know what thread pitch/type thermistor to order for the PTU, I can handle the wiring and mounting the gauge, I just need to know the thread for the plug

 

[Blown]

You are fine.

Steve I think was trying to help with having you look-up a non-existing replacement part to measure it for size????????? I don't know but he was not helpful and questioning you. I would have to pull the fill plug to check it.

It sounds like a decent idea. I would be curious of the temps it reaches. It appears anything over 275 could be an issue.

 

[15ExpLimited]

You are fine.

Steve I think was trying to help with having you look-up a non-existing replacement part to measure it for size????????? I don't know but he was not helpful and questioning you. I would have to pull the fill plug to check it.

It sounds like a decent idea. I would be curious of the temps it reaches. It appears anything over 275 could be an issue.

yeah for sure I was able to deduce how hot they get just off of looking at it and understanding them, but I went off-roading for a few hours and even after driving on the highway for 10~ minutes when hitting the PTU with a bit of water accidentally to get some mud off my subframe it vaporized and turned to steam instantly on contact so I know that it’s getting *really* hot in there, I might go to a dealer and just order a replacement fill plug and either get a tap and die set and just compare the threads side by side or go to a Parts/Home Store and use their thread match tool panel thing, Because IF I can get a temp sensor that fits, it’s just a matter of running the single wire from under the car along the O2 sensor wiring to the interior, finding a rectangle digital temp gauge, mounting it under the dash beneath the tow haul/park assist/trunk release button, and using a fuse panel tap on a SAFE and reasonable circuit to pull power from and there you go, PTU temp sensor, that’s currently what I’m rotating in my brain blander in 3D at the moment, I’ll update further if I get my hands on a drain plug or the thread type

 

[Steve8316]

I’m realizing that the mobile version of this website is not the best way to interact or use this...

I never use a phone for browsing, shopping, or posting; always a desktop with a big screen and adblock. It makes a difference.

...I know the that the flashpoint of 75W-140 is 375~ F...

The temperature to know is where it stops doing its job, or at which PTU damage begins. Just knowing that it's "hot" or "hotter" isn't useful, so I still don't think a thermometer will help you until you find those temperatures to watch for.

...a non-existing replacement part to measure it for size?

My '16PIU has a factory temperature sensor, so the part exists and can be measured.

...I would have to pull the fill plug to check it.

Since he said in the original post that he HAS changed the fluid, he already knows how to pull the plug, so he can measure those threads.

I would be curious of the temps it reaches.

That was my point - this is a matter of curiosity; not functionality, since he doesn't know what temperature to watch for.

It appears anything over 275 could be an issue.

Where did you cook up that number? What do you think will happen at 280°F?

...when hitting the PTU with a bit of water accidentally...it vaporized and turned to steam instantly on contact so I know that it’s getting *really* hot in there...

There's barely an inch between the PTU & the rear cat, so the steam almost certainly came from the cat; not the PTU.

...it’s just a matter of running the single wire from under the car along the O2 sensor wiring to the interior, finding a rectangle digital temp gauge, mounting it under the dash beneath the tow haul/park assist/trunk release button, and using a fuse panel tap on a SAFE and reasonable circuit to pull power from...

...or maybe installing a direct-replacement sensor and wiring it in the way Ford did on mine, and then monitoring it with some OBD2/PID-type gauge. In that case, you wouldn't need to know the thread size because it already fits. You'd only need to know the temperature limit.

 

[15ExpLimited]

I never use a phone for browsing, shopping, or posting; always a desktop with a big screen and adblock. It makes a difference.

The temperature to know is where it stops doing its job, or at which PTU damage begins. Just knowing that it's "hot" or "hotter" isn't useful, so I still don't think a thermometer will help you until you find those temperatures to watch for.

My '16PIU has a factory temperature sensor, so the part exists and can be measured.

Since he said in the original post that he HAS changed the fluid, he already knows how to pull the plug, so he can measure those threads.

That was my point - this is a matter of curiosity; not functionality, since he doesn't know what temperature to watch for.

Where did you cook up that number? What do you think will happen at 280°F?

There's barely an inch between the PTU & the rear cat, so the steam almost certainly came from the cat; not the PTU.

...or maybe installing a direct-replacement sensor and wiring it in the way Ford did on mine, and then monitoring it with some OBD2/PID-type gauge. In that case, you wouldn't need to know the thread size because it already fits. You'd only need to know the temperature limit.

Steve, I appreciate your detailed response, I didn’t exactly “cook up” the number in the sense that I just imagined it, but rather the 250-275F number is a number that I used after referencing the limits of when 75-140 begins to break down, the peak, temps and equilibrium of ford PTU’s and also directly consulting and reading other owners & posts who have not only modified and worked on the D3/4 platform PTU’s but the smaller lighter duty C1 platform PTU’s as well, so while I might not have the “magic number” to satisfy whatever you might have in your head, BUT what I do know is I atleast have a general window of what’s an okay and not an okay temperature for it, again mishimoto and other 3rd parties did a pretty good job extensively datalogging the temperatures of RDU’s and PTU’s in their own vein of figuring out solutions to these factory problems ford served us on a silver platter so while I cannot say that the conditions are the same for a focus RS liquid coooled PTU it’s still ford design and the same general knowledge and principals can be applied from one to another with the use of some common sense, and unfortunately my knowledge of wiring/cars ends at modifying and adding sensors to OEM systems, I know PIU’s and TT Ecoboosts use a cooling sensor on the PTU but afaik it’s in a different spot as the PTU’s seem to just be different comparing civilian N/A PTU’s to PIU and Ecoboost ones, the factory “cloaca” fill/check/suck from port on civillian N/A’s is right against the gear (for lack of a better word) for the output on the driveshaft to the RDU, there’s unfortunately zero room to get anything other then the factory flat plug in there, I couldn’t even get my finger in directly, I had to run my finger to the side in order to clear it, so unless the PTU is tapped somewhere else lower/upper on the case, the factory plug on the N/A non PIU PTU is unfortunately not a suitable location for a temp sensor.

 

[Blown]

I did a quick search to reveal when 74w140, synthetic, gear oil starts to breakdown due too heat also known as "Thermal Viscosity Breakdown".

Gear oil temp tolerance?

Related to the below discussion about Ford PTU's but does anybody have any idea when type of operating temp ranges a GL-5 gear oil is designed for? Specifically a 75w140... more specifically Amsoils SG 75w140?

bobistheoilguy.com

From Bob is the oil Guy forum:
"What is the peak operating temperature of Ford's PTU?

For most lubes, any sustained temps above above 70% of the flash point is going to severely degrade the lube. So for this fully synthetic 75W140, any temp > about 280F is detrimental.

As others have stated, the Ford PTU design suffers from two main issues: 1) the low volume of fluid, 2) insufficient heat rejection.

Without an external cooler, short OCI's would be in order."

 

[Steve8316]

...the factory “cloaca” fill/check/suck from port on civillian N/A’s is right against the gear (for lack of a better word) for the output on the driveshaft to the RDU, there’s unfortunately zero room to get anything other then the factory flat plug in there...so unless the PTU is tapped somewhere else lower/upper on the case, the factory plug on the N/A non PIU PTU is unfortunately not a suitable location for a temp sensor.

So then the answer to your original question...

...the thread pitch of the PTU's fill port? would it be possible to thread an aftermarket temp sensor in place of the old fill port...?

...is "no". It would not be possible.

And to drill/tap the PTU, you'd have to remove & disassemble it (to find a thick spot in the case where the sensor could be threaded in & not interfere with internal moving parts). At that point, nothing about the original plug threads would be relevant. You'd have to match your new drilled hole to the threads on whatever sensor you buy to work with your gauge. So that question is now entirely moot, and you can focus on what temperature you plan to use as your "redline".

...temps above above 70% of the flash point is going to severely degrade the lube. So for this fully synthetic 75W140, any temp > about 280F is detrimental.

Severe degradation isn't necessarily the target, though. I'd be more interested in ANY degradation that would reduce the oil's lifespan below the normal maintenance interval.

...250-275F...when 75-140 begins to break down...

That's a pretty-wide range for "beginning" to break down, and it seems like 275 is a justifiable number for extreme breakdown. IDK where 250 came from, but if that's the number you want to use, it sounds like you're ready to choose your gauge & sensor that respond well to that temperature. Have you started shopping for either? Are you planning to disassemble & machine the PTU yourself? Are you going to do it to the current PTU, or try to find a JY unit to mess with?

All of that seems pretty complicated, expensive, & labor-intensive to me. I think if I do anything to mine, it'll be to increase fluid capacity & cooling. Possibly by plumbing in a cooling loop from the drain plug up to the radiator fan, and back to the vent hole, with a low-pressure 12V pump. Even if the pump failed, the PTU would still have its normal fluid and would still work as-designed for the same miles. But the added plumbing would make fluid changes quicker & easier. And that would be the opportunity to test the pump regularly.

 

[Blown]

You didn't read what I linked too and seem to want a special number just for you to approve of. Severe degradation begins but does not happen all at once and fast like at the temp I researched and posted to help, piss off with your analysis!



Just run 75w160

 

[Steve8316]

... piss off with your analysis!

You first.

 

[Blown]

I think it a good idea to be able to monitor PTU temps and especially if you are ‘wheeling’ it more. Ford thought about it enough to put a sensor on the Police units. That said I don't think it is worth the effort to add one for my use. I won’t be ‘wheeling’ this one hard at all so don’t fear the heat so much, but why not have the added protection if ever needed in a higher temp oil?

Overheating the PTU, viscosity breakdown and PTU failure is the concern. Why not use a gear oil that will take more heat? The 75W190 Maxima Oil Pro Gear Oil 49-469128 has a Flash Point “Greater than 450°C (D92)”. Great than? Let's call it 450 Celsius, multiply by .70 to get the temp at which thermal breakdown happens according to the Oil Guy = 315C or converts to 599F (degrees Fahrenheit). That is around double the heat resistance compared to Valvoline synthetic 75w140 I used. The Valvoline has a 290F flash point and 273F for thermal breakdown............................. I will change to the 75w190 this Spring, check-up on it after some use and keep-up with changing it at least every 30k.

 

[15ExpLimited]

I think it a good idea to be able to monitor PTU temps and especially if you are ‘wheeling’ it more. Ford thought about it enough to put a sensor on the Police units. That said I don't think it is worth the effort to add one for my use. I won’t be ‘wheeling’ this one hard at all so don’t fear the heat so much, but why not have the added protection if ever needed in a higher temp oil?

Overheating the PTU, viscosity breakdown and PTU failure is the concern. Why not use a gear oil that will take more heat? The 75W190 Maxima Oil Pro Gear Oil 49-469128 has a Flash Point “Greater than 450°C (D92)”. Great than? Let's call it 450 Celsius, multiply by .70 to get the temp at which thermal breakdown happens according to the Oil Guy = 315C or converts to 599F (degrees Fahrenheit). That is around double the heat resistance compared to Valvoline synthetic 75w140 I used. The Valvoline has a 290F flash point and 273F for thermal breakdown............................. I will change to the 75w190 this Spring, check-up on it after some use and keep-up with changing it at least every 30k.

Reading this is definitely a surprise and a bit worrying as I also put Valvoline 75W-140 into my PTU as well. Hearing that the breakdown temp point is 273F, a little too low for a ford PTU imho, I agree I’ll try some sort of severe rated 75W-160 with a high breakdown point or a 190 weight oil in my PTU as well, it really bums and pisses me off to such a degree that these civillian PTU’s don’t have any form of a drain plug, and I’m not exactly keen on paying out the ass for some some sort of pressurized fluid extractor, I’ll end up just topping it off with 190 every time I change my engine oil or get underneath of it for whatever reason as it’s got a bit of a weeping leak on the driveshaft output seal anyway.

 

[Blown]

I was not interested in getting a pump till I saw what a weak point these PTU's can be. There are hand pumps, but I only paid about 25 for a little 12 volt vacuum pump. It's not great quality but I will only use it a few times, not commercially. It was relatively easy to get a tube into the fill plug of the PTU and down into the oil. It was quick, I was able to use it to pump new fluid in and topped it by hand. The viscosity will breakdown over time. especially driving it hard. I did add a little performance and larger wheels to load the PTU up more. I am planning to change the PTU oil every 30k at least but will check it this spring.................................I've added mods and will get to some light wheeling before I look at it again.

Good luck with it!