I’m installing a Smiths mechanical oil pressure gauge in my 1969 S2 Coupe because the electric senders are not always accurate and I thought I could at least see how accurate it is. I purchased all the necessary fittings that I thought I needed and they are shown in the photo below.
The brass T piece has 1/4 BSPP (parallel) threads at both ends (male/female) and a 1/8 NPT in the side. An adaptor 1/8NPT x 1/8BSP (male/male) connects to the side of the T and then via a flexible oil pressure pipe to the Smiths Oil Pressure gauge.
My problem is that when I tried to install the T into the top of the oil filter housing it wouldn’t screw down. I then noticed that the electric oil pressure sender has a 1/4 BSPT thread (tapered thread). I thought that the female thread in the oil filter housing was a 1/4 BSPP (parallel thread).
Could the oil pressure sender 1/4BSPT have damaged the thread in the oil filter housing or is the thread in the housing tapered and I just need a different T with tapered threads?
I’m pretty sure the sender should have a BSPP (parallel) thread. Are you sure yours has a tapered thread? If so, is it original, or an aftermarket part? If it is an aftermarket part I wonder if it is actually 1/4 NPT, which has 18tpi rather than the 19tpi of BSP(P or T). I’ve seen some aftermarket parts (though not these senders) where the thread type has been incorrect and presumably deemed “close enough” by the manufacturer/vendor - e.g. wheel brake cylinders for my XK-140. I say this as I doubt that a 1/4 BSPT sender would damage a 1/4 BSPP hole to the extent that a true 1/4 BSPP would bind in it. However, if someone forced a 1/4 NPT male into the 1/4 BSPP female, the differing thread pitch could well damage the female thread making it bind on a 1/4 BSPP male thread. I think someone else reported using one of these 1/4 BSPP Ts successfully earlier this year, so something seems wrong here.
Probably a dumb question but could you leave the old oil pressure sender in as a plug and use one of the galley plugs on the side of the engine for your new direct reading gauge? IIRC they are 14"BSPP.
Andy this is the tee fitting I got that they said should work for the E-type but with the hurricane, work and travel since I got it I have not had a chance to try to screw it into the filter housing location on my car yet. My old sending unit screws in fine though. Is this the same one you have ?
Andy, its definitely BSPT, at least on my 69. The US fitting will allow you to thread it in, but won’t seal well. (18 v 19 pitch). Coating the underbody with a fine dirt attracting oil mist. Don’t go to the hardware store for it. (as we say “ask me how I know this”)
I think I got the fitting at McMaster-Carr.
You might check with Mike Frank: he knows the correct dia/pitch/thread.
Are you saying that it’s definitely British Pipe Thread, but you’re not sure if it’s Parallel (BSPP) or Tapered (BSPT)? If so, I agree with the first part (British Pipe Thread) and am as sure as I can be that it is Parallel, NOT Tapered. Hence my question to Andy (the original poster) about whether he is sure his sender has a tapered thread, and if so, is it original. Still waiting to hear back…
an easy tell it is parallel thread is by the fact the sender has a sealing washer on it, the sender screws all the way in and the copper washer seals the fitting. tapered fittings just force fit themselves to seal. you can screw tapered fitting in, but depending on how far you force it you may have a hard time going back to just the standard pressure sender.
you can find the correct adapters at McMaster-Carr. p/n 4936k119 or 4936k413
and look close, you will notice the BSPP side has a sealing washer. the BSPT does not.
Guys thanks for all your responses and confirmation that it is indeed a 1/4BSPP. The sender unit that I presently have installed is from Nisonger and is “made in England and is supposedly a Jaguar unit”. It’s sold as 1/4BSP and I installed it with a copper washer but when I removed it and measured the thread its definitely tapered.
I’ll remove the entire oil filter housing to check out the condition of the female thread and at the same time can clean the pressure relief valve.
BTW David B I also got my fittings from Merlin Motor Sports in the UK. I thought they were very reasonable in price and came in 1 week.
Andy I finally got around to test fitting the tee fitting I got from Merlin Motorsports. On my Feb 1968 engine it screws in OK finger tight with the same feel as the sending unit. I bought a few extra of the p/n M-COP-4 copper crush washers that they said I should use with their tee fitting. I have not bought the mechanical gauge kit that I am am going to use with it yet so I cannot report that every thing seals up and works well but so far see no reason on my car it will not work OK.
Based on your replies I went ahead today and installed the brass T that I bought from Merlin Motorsports and it screwed right in perfectly. I connected up a remote oil pressure gauge using the other pieces I also bought from Merlin and attached the oil pressure gauge temporarily to the bulkhead. I wanted to ensure that everything worked and didn’t leak.
There is a 5-10 psi difference between the electric OP gauge depending on oil pressure and the mechanical one. The mechanical one reads higher.
This photo shows the OP gauge on the firewall at 1500 rpm engine cold. OP is 50psi.
Hi David you didn’t misunderstand anything. When I first tried to install the brass T I was a little timid when I tried to screw it down and it wasn’t going in as easily as I thought it should. I then noticed that the sender unit had a tapered BSPT thread and I wondered if that had damaged the threads. Thanks to all of the posts I was reassured that it should fit and with a little more effort on my part it DID screw into the top of the oil housing like it should.
I’m confused. What’s wrong with the mechanical O/P gauge face? Just install the mechanical gauge in dash in place of electric one and route O/P line up to back of gauge. I did that and used a 90 degree ell fitting on back of gauge to simplify routing of O/P tubing up to gauge panel.
Is it just that you’d rather have the 20-4-60 intervals instead of 0-50-100? 50 or 50+ is a very nice pressure!
The final “set-up” is entirely a matter of personal preference…so its not really a matter of confusion. I went this way a while back on my1970S2E. I kept the oe gauge in the dash, because it looks “nicer”, and also had the “live oil” gauge on the firewall. I think overall I would regard the live oil gauge as being more reliable over time than the Smiths gauge…but in the end neither of the gauges are calibrated, and it really doesn’t matter.As long as you get repeatable behaviour from day to day, then you know things are OK. But pay attention if either one of them shows a different reading!