Oil Pressure Sender Advice

[skippydiesel]

Had this request for advice under Engines & Props without any response - hope to get lucky this time.

 

Engine - ROTAX 912 ULS (100 hp)

 

After 18 years & 800 hrs, suspect oil pressure gauge or sender may be starting to degrade. Thought I would start by replacing the sender.

 

My existing (unmarked) pressure sender has what appears to be parallel male 9.67mm wide/thick (10mm?/) x 9mm long (measured using callipers) threaded connection.

 

This" drives" a Speco 0-100 psi gauge that is rated at:

 

0 psi - 240 ohms,

 

50 psi -103 ohms

 

100 psi - 33 ohms

 

Speco do not do a metric threaded sender.

 

Initially it appeared that I may need one of the two following senders:

 

VDO PN 360-022, 500 KPA, 75 psi, 10-183 ohms, M10 x 1.0, Screw 4mms terminal, (About $60.00)

 

OR

 

VDO PN360081032002C,0-5 BAR, (75 psi), 10-180 ohms, M10 x .0, 2 screw 4mms terminal, (About $150.00).

 

VDO advise little difference in the above other than manufacturing location and the more expensive one will drive a warning light from the second terminal.

 

Further, VDO advise the above senders will reverse the reading on my Speco gauge.

 

Have found advice suggesting a VDO PN 360-023 is the correct sender however this is not available from VDO.

 

Comments suggestions welcome and yes I realise I may have to replace both gauge & sender if compatibility continues to be an issue.

 

 

[cscotthendry]

I'm a bit puzzled by what you mean by "degrade". Are you seeing erratic readings, or just lower than normal readings? If they're just lower than normal, I'd have a look at other aspects of the engine to make sure that excessive wear is not causing the problem.

 

To replace the sender, if Speco do not do a metric thread sender, it may still be possible to use one, by getting an adapter, either buying one or getting one made by someone.

 

 

[skippydiesel]

I'm a bit puzzled by what you mean by "degrade". Are you seeing erratic readings, or just lower than normal readings? If they're just lower than normal, I'd have a look at other aspects of the engine to make sure that excessive wear is not causing the problem.To replace the sender, if Speco do not do a metric thread sender, it may still be possible to use one, by getting an adapter, either buying one or getting one made by someone.

Thanks Scott:

 

When I acquired this aircraft (about 8 years ago) I was worried by the 30 psi engine oil read out on my Speco oil pressure gauge - Bert Flood advised that all was okay.

 

After the 700 hrs service I notice, a small (2-5 psi) drop in indicated pressure (small gauge hard to estimate). Plumbed in a "master" gauge found that oil pressure to be about mid range for Rotax 912, 45 psi @ 4000 rpm, all okay, Speco under reading by about 15-20 psi. Small drop in pressure put down to change in AeroShell Sport Plus 4 formulation (black - red bottle).

 

Still I didn't like the small drop & the 15-20 psi under reading or the occasional unexplained momentary drop in pressure - decided to change sender @ 800 hr service. Tried to find sender to suit - no luck (as yet) and no off the shelf adapter to suit. Anyhow an adapter may extend the sender location, compromising fit.

 

My research suggests that amongst the indicators for a failing oil pressure sender & gauge are - low, erratic and small drop/rise in reading.

 

800 hr & 5 year rubber service just completed - engine runs very smoothly, no significant oil consumption (do not need to add oil) between services, plugs coffee brown, no change in running temperatures in climb/cruise, carbis balanced, etc etc & all operating indications within acceptable parameters.

 

Now you have full story.

 

I may have to "bite the financial bullet" & purchase a new sender & gauge (probably VDO as they sell 10mm metric senders,)

 

 

[Downunder]

The oil pump housing thread was changed by rotax in about 2013(I think) to the metric fine 10x1.00mm(from 1/8 npt) because they moved to the "keller" pressure sender(the current rotax sender). Previously the black "honeywell" sender and before that the vdo (with brass anti vibration ring).

 

Your pump housing, being 10x1.00 would either have been tapped out previously or be a "new" type housing.

 

As the oil pressure is probably the most critical indicator on the engine, I would recommend going with the Rotax keller sender and finding a gauge to suit.

 

My honeywell failed some time ago and the keller is working fine.

 

The vdo's although cheap have a history of failing when mounted direct to the engine but seem fine when remote mounted.

 

 

[cscotthendry]

Skippy:

 

I just remembered that I have an old Honeywell sender here and I decided to measure the thread. It mics out at exactly 10mm, but the thread pitch looked like a 28Ga on my thread gauge. So I'm not sure what the actual thread is. It might be some kind of pipe thread. It was definitely not a 1.0, 1.25 or a 1.5mm thread which seems to rule out being a standard metric thread for 10mm.

 

 

[Downunder]

It is a 1/8npt x 27. Close to 10mm but not 10mm.

 

 

[skippydiesel]

It is a 1/8npt x 27. Close to 10mm but not 10mm.

According to Dr Google -. 1/8NPT converts to 6mm. A long way from my 9.67mm.

 

3/8 is the closest imperial measurement to 9.67 mm but no pressure senders in this size.

 

I am almost illiterate when it comes to imperial measurements and wish that whatever Gods may be out there , change everything to metric - YESTERDAY!!

 

 

[skippydiesel]

The oil pump housing thread was changed by rotax in about 2013(I think) to the metric fine 10x1.00mm(from 1/8 npt) because they moved to the "keller" pressure sender(the current rotax sender). Previously the black "honeywell" sender and before that the vdo (with brass anti vibration ring).Your pump housing, being 10x1.00 would either have been tapped out previously or be a "new" type housing.

As the oil pressure is probably the most critical indicator on the engine, I would recommend going with the Rotax keller sender and finding a gauge to suit.

 

My honeywell failed some time ago and the keller is working fine.

 

The vdo's although cheap have a history of failing when mounted direct to the engine but seem fine when remote mounted.

Thanks for all this - my aircraft was commissioned in 2000, so I assume the engine is 1999/2000. Further assumption, if no changes/mods to oil pressure sender fitting it should be a 1/8 npt. Unfortunately this does not seem to match my measurement (as above)

 

In my experience (limited to one) cheaper, still than VDO, Speco oil pressure gauge & unknown sender direct mounted, have stood the test of time (18 years/800 hrs) very well.

 

 

[Downunder]

Yes, it should be 1/8 npt. "1/8" is not a representative measurement of the actual thread.

 

This is a pic of a 10x1 banjo bolt and 1/8 npt male end.

 

 

 

[skippydiesel]

Thanks Downunder - could have sworn mine had parallel, not tapered thread, but then again I am now (very) unsure, so I will have to get it out of the engine and carefully measure.

 

 

[Downunder]

Yes, it should be tapered.

 

Just to confuse it more, a straight npt is called a nps....

 

Then bsp is only 1 tpi from npt, 28 vs 27...lol...

 

So there is probably several diffrrent sensor threads that could forced into the 1/8x27 npt Rotax oil housing thread ....

 

 

[Blueadventures]

Had this request for advice under Engines & Props without any response - hope to get lucky this time.Engine - ROTAX 912 ULS (100 hp)

 

After 18 years & 800 hrs, suspect oil pressure gauge or sender may be starting to degrade. Thought I would start by replacing the sender.

 

My existing (unmarked) pressure sender has what appears to be parallel male 9.67mm wide/thick (10mm?/) x 9mm long (measured using callipers) threaded connection.

 

This" drives" a Speco 0-100 psi gauge that is rated at:

 

0 psi - 240 ohms,

 

50 psi -103 ohms

 

100 psi - 33 ohms

 

Speco do not do a metric threaded sender.

 

Initially it appeared that I may need one of the two following senders:

 

VDO PN 360-022, 500 KPA, 75 psi, 10-183 ohms, M10 x 1.0, Screw 4mms terminal, (About $60.00)

 

OR

 

VDO PN360081032002C,0-5 BAR, (75 psi), 10-180 ohms, M10 x .0, 2 screw 4mms terminal, (About $150.00).

 

VDO advise little difference in the above other than manufacturing location and the more expensive one will drive a warning light from the second terminal.

 

Further, VDO advise the above senders will reverse the reading on my Speco gauge.

 

Have found advice suggesting a VDO PN 360-023 is the correct sender however this is not available from VDO.

 

Comments suggestions welcome and yes I realise I may have to replace both gauge & sender if compatibility continues to be an issue.

Is this any help $88-00 ? Rotax 912 914 CHT & Oil Temp Coolant Sender Sensor Aircraft Ultralight Engine | eBay

 

 

[onetrack]

Here is a VDO 360.081/032/008 sender, which has a 1/8" NPT thread and is apparently the one for the Rotax.

 

Rotax 912 914 Engine Oil Pressure Sender Sensor Ultralight Aircraft Microlight | eBay

 

Skippy, do you have a photo of your sender? I possess a collection of new (mostly VDO) senders in my workshop, that are not in boxes, but which have been vacuum-sealed in plastic.

 

I have no idea what is in the sender collection (which I purchased when a tractor/engine reseller folded), but I could have a look to see if there's anything suitable in there.

 

I think I might also have an older VDO catalogue which could provide more detail on the different varieties and types available.

 

 

[Downunder]

The problem it seems is that his gauge and sender are not a normal Rotax setup.

 

Most gauges are configured for a "normal" Rotax sender electrical out put, whether vdo, honeywell or keller.

 

His ohm range seems to be working in reverse of standard.

 

 

[cscotthendry]

Is this any help $88-00 ? Rotax 912 914 CHT & Oil Temp Coolant Sender Sensor Aircraft Ultralight Engine | eBay

LOL, No help at all Mike. He's looking for a pressure sender.

 

 

[cscotthendry]

Yes, it should be 1/8 npt. "1/8" is not a representative measurement of the actual thread.This is a pic of a 10x1 banjo bolt and 1/8 npt male end.

[ATTACH=full]52632[/ATTACH]

That's what I *love* about plumbing. Like Heinz baked beans ... 57 varieties, and nothing fits anything else.

 

 

[skippydiesel]

Yes, it should be tapered.Just to confuse it more, a straight npt is called a nps....

Then bsp is only 1 tpi from npt, 28 vs 27...lol...

 

So there is probably several diffrrent sensor threads that could forced into the 1/8x27 npt Rotax oil housing thread ....

Okay just come from aircraft have removed and remeasured sender:

 

Length of threaded section 9mm

 

Width (over thread) at base 9.56mm - Width at tip 9.62 mm

 

Thread pitch 0.9 mm

 

SOOOO its parallel & has a metric thread.

 

To confuse matters: There is evidence of aluminium thread embedded in the sender threads. To me this is suggestive of incorrect fit.

 

Obviously I have been dwelling on this matter for some time - the comment by my VDO technical advisor that a VDO sender would drive my Speco gauge in reverse suggests to me that the sender MUST be compatible with the gauge - SOOOO the sender must be a Speco. The system has operated for 800 hrs/18 years without leaks but it does seem that the original builder must have either "forced" the sender to fit OR tapped the oil pump housing.

 

Current Speco senders are all 1/8NPT

 

Any chance you could give me actual measurements of the 1/8 NPT so that I might be able to guess at a likely fit or not.

 

 

[cscotthendry]

At the base of the thread it is 10.29mm. At the tip it is 9.60 (approx). Thread pitch too hard to measure with calipers, but shows 28GA on thread pitch gauge.

 

From your measurements, it looks like you might have a 10mm X 1.0 sender. Anybody's guess what's in the oil pump given that you say you have AL adhering to the sender threads!

 

 

[Downunder]

Sounds like a 10x1...

 

If it helps, the 10x1 bolt will screw into a 1/8 npt female about 1 to 2 turns.

 

Obviously the 1/8 tapers down so therefore gets tight.

 

As the oil pump housing is aluminium and the sender steel, it could have been forced I guess.

 

But you wouldn't expect to get very much thread depth. How far did it go it?

 

If the housing was 10x1, and sender 10x1, then it would continue to screw in to the shoulder of the sensor. If it screwed in and got tight without "bottoming" then theres mismatched threads, or (one or both) are tapered.

 

 

[onetrack]

Below is the NPT and BSP thread reference and measurements chart. These are the two most common pipe threads, and the two most-commonly mixed up.

 

Metric pipe threads are relatively uncommon - even the Japanese and Germans regularly use NPT and BSP in their pipe threads. Metric pipe threads are tapered threads.

 

Explanation of common threads including BSP & NPT

 

Here's an extensive thread system explanation with accompanying charts for all thread types.

 

THREAD IDENTIFICATION CHART

 

When examining threads, it's very important to obtain and use a thread chart, and a thread pitch gauge. You can even get the gauges from Supercheap.

 

Toledo Thread Pitch Gauge Set 2 Pc - 301067 - Supercheap Auto

 

 

[skippydiesel]

My width measurements are pretty well spot on.

 

The thread pitch was measured using a metric pitch measuring tool so is also spot on (there may of course be an imperial equivalent - could it be 28GA ??.)

 

So the sender fitting is definitely not a 10 x 1

 

To answer Downunder - the full 9mm length of the threaded section screws to the shoulder.

 

From Scotts information I am wondering if the 1/8 NPT might just fit - it will depend on the thread pitch. If the 0.9 mm thread is a close match with 28GA it may be possible to fit the 1/8 NPT

 

 

[skippydiesel]

Photos of the offending beast

 

 

 

[cscotthendry]

It would be easy and cheap enough to test the 1/8NPT. Just buy a general brass 1/8NPT fitting from an auto parts store and see how it fits.

 

 

[Blueadventures]

Okay just come from aircraft have removed and remeasured sender:

 

Length of threaded section 9mm

 

Width (over thread) at base 9.56mm - Width at tip 9.62 mm

 

Thread pitch 0.9 mm

 

SOOOO its parallel & has a metric thread.

 

To confuse matters: There is evidence of aluminium thread embedded in the sender threads. To me this is suggestive of incorrect fit.

 

Obviously I have been dwelling on this matter for some time - the comment by my VDO technical advisor that a VDO sender would drive my Speco gauge in reverse suggests to me that the sender MUST be compatible with the gauge - SOOOO the sender must be a Speco. The system has operated for 800 hrs/18 years without leaks but it does seem that the original builder must have either "forced" the sender to fit OR tapped the oil pump housing.

 

Current Speco senders are all 1/8NPT

 

Any chance you could give me actual measurements of the 1/8 NPT so that I might be able to guess at a likely fit or not.

Have you thought about chasing up a brass adaptor so you can thread the 'Speco' sender into it and then screw into the rotax. i'm sure ENZED may have one or a fitter could make one up. Another way may be to buy a metric brass plug of the thread size that screws into the rotax and drill and tap it 1/8 NPT for the 'Speco' sender. I'm 100% sure that will be a suitable fix (Just make sure that there is plenty of metal left around the meeting of the threads area as if its thin vibration and time will result in a failure. Cheers Mike

 

 

[bstrachan]

Recently my buddy Rex noticed oil pressure fluctuations on his brand new Rotax 912ULS. He has the Grand Rapids Technology EIS and the housing of the oil pressure sender on his new engine is physically different than the VDO I have. However the pipe thread that goes into Rex's oil pump LOOKS the same as mine.... today is the first I'd heard that Rotax had changed this pipe thread. I'm not sure I believe this, in fact. Whatever, I removed the "new style" sender from Rex's brand new 912 and screwed in a small mechanical gauge which is 1/8-27 NPT. Went right in, didn't leak. Also the VDO sender (P/N 360-004) is 1/8-27 NPT, says so right on the package. (I keep a spare on hand, I've had to replace a couple of these already. If you mounted the sender remotely as the instructions tell you to do, rather than screwing it into the oil pump the way Rotax does, the sender might last longer.) Long story short, I attach a photo of the 360-004 sender and the 1/8-27 NPT mechanical gauge screwed into a 1/8-27 NPT tee fitting. Note that this is the exact same mechanical gauge that was temporarily installed in the new 912ULS, and the VDO sender is an exact replacement for the one in my 2006 912ULS. From all the above, I conclude the female thread on the Rotax 912 oil pump, old (my 2006) or new, is 1/8-27 NPT. Take it for what it's worth. BTW, VDO is very adamant that the 360-004 IS NOT FOR AIRCRAFT APPLICATIONS. Good old Rotax.