With Wings As Eagles: Craig P. Steffen's Blog

caveat emptor

2009 February 26 22:45

One of the problems of buying stuff for a vintage car is that except for the most basic items, you have to order parts from one of the very few dealers of those parts. Combined with the fact that dune buggy magazines have (apparently) promoted a lot of additions to Bugs that are a bad idea (chrome parts don't cool as well as black ones). So there's a range of vendors, from bad to good.

Unfortunately, as much as I like their facility, Mid-America Motorworks is one of the bad ones. There are definitely good stuff to be had there, and I really like the VW events. I like their on-line catalog too. Unfortunately, their catalog has some stuff that's poor quality, and some things that are just the wrong parts for the job.

I recently ordered an oil pressure gauge setup from them. Here is the relevant page on their site. It has two oil pressure senders listed, a single post and a double-post. I think the the idea is that the single post one can control the gauge, and the double-post one can run the gauge and the dash warning light. However, I've heard that the double-post ones don't drive the gauge properly, and that the correct way to do it is to have "T" attached to the oil passage and have the stock VW pressure switch run the warning light and a separate sender run the gauge. So I bought the "T" fitting from that page, and the oil pressure gauge and the single-post sender. Let me stress here that this catalog is specifically for air-cooled volkswagens.

So here's the stock oil pressure switch in my engine that's sitting on my work bench:

The switch has a terminal that sticks out. When there's no oil pressure, the terminal connects to the switch body and so to ground, making the oil light turn on. When the engine is running, oil pressure enters the switch and compresses a diaphram that disconnects the terminal from the switch body, making the light go out. If oil pressure drops, then the terminal grounds out and the light goes on again.

So, here's the T fitting screwed into the place where the switch normally goes.

Here's what the sender looks like.

A narrow end that screws into the block (or into the T) and then the other end has the electrical contact.

Here's what the final setup would look like. One fitting, connecting the oil supply gallery to two different sensors.

Unfortunately, this is not all wine and roses. The sender that I have doesn't seem to want to screw into either terminal in the T fitting, nor into the block in place of the stock switch. Something's up. Here you can see that the pitch of the sender threads don't match those of the brass T.

Wheras the stock switch and the T match perfectly

Huh. One thing that I noticed and got me thinking; it looks like the sender has a marking that indicates its thread specifications:

What's interesting is that alhtough it says 1/8", the diameter the screw part is more like 3/8 of an inch. It turns out that's just the way it is; as shown in this table, diameter of 1/8 NPT threads is .405 inches. The beetle is a german designed car, and most of the screws and fittings on it are metric, so this is surprising.

Well, it turns out that the thread spec on the sender that Mid-America sends out is just wrong. I figured it out at California Import Parts:

here's the sender that I need, with M10x1.0 threads (metric)(which they mention fits the stock location)

Heres' the sender that I got, which does NOT fit the stock location. I would be really nice if Mid-America could at least mention that the sender they have is not the stock thread set.

So I guess I'm going to sell this one on ebay, I guess, and then buy one that fits.