Crawls Backward (When Alarmed)

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Installing Oil Pressure Gauge in the SAAB c900

I'm waiting on some bits for the banjo mandolin, so I needed to find some other project to work on.  I have a short list of stuff left to do on the SAABmarine, so I worked on a couple of things.

One of them is actually connecting the senders/sensors for the oil pressure and water temperature gauges.  You may recall that a while back, I put the gauges in the dash, and ran the tubing for the gauges, but didn't connect them.

I'm going to connect the oil pressure gauge first, since it will be a bit less daring than the water temp.

We need to remove the factory oil pressure warning sender.  First, we disconnect the hot lead from the sending unit.  You can see the blue arrow pointing to the connector - I've already pulled the wire off at this point.

You can also see the sender has a big hex on it - which is what we'll need to undo.

Digression here: for those of you who own (or have owned) English cars with wire wheels: you know about 'undo' - it's on the wheel nut with an arrow indicating which way to remove the nut.

Do Ferraris with Borrani wheels have a similar instruction?  I have no idea.  I have never had a tool in my hand within striking distance (ha ha, striking) of a Ferrari.

The nut is 24mm.  I suppose you could use an open-end wrench, but as a relatively experienced SAAB mechanic, I have the proper tool - a deep-well 24mm socket.

The perfect thing for the job.

Funny how that wide angle setting on the camera lens makes close-up stuff look huge.  That wrench looks like it's about 50cm long!

Or the car has suddenly shrunk.

Here's the sender after removal. Piece of cake.

Mmmm.  Cake.

Now, this is the factory sender for the oil warning light on the dash - the one that lights up when your oil pressure is like 5 lbs or below.  Meaning: Stoppa motorn nu!

I am basically daring to run without a warning light.  I actually have a bunch of adapters which will let me use the new gauge connectors AND the factory light, but right now, I'm just connecting the new gauge.  Time will tell if I bother to reconnect the old warning light. I'm starting to think since I have a gauge I'll be ok.

Here's the new connector that goes into the engine block.  There's a little brass ferrule that goes over the hose and seals the thing up tight.

Then the outer nut tightens up over it.  The business end screws into the block.

We need to put some thread sealer on the threads so they won't leak.  This is a mechanical gauge, so oil goes into the hose.  We don't want leaks.

I tightened the block nut first, then the top (hose) one.

This picture makes it look so easy, doesn't it?  Let me tell you, this was a beast.  I could only turn the nuts about a quarter of a turn before the wrench contacted the dipstick tube.  Took a while to get them tightened up.

We don't need a lot of torque on these pieces - the little ferrule might get crushed.  We have to treat the ferrule with caution, bless its little brass head.

The gauge end, inside the car, is a whole lot easier to connect, since we have complete access to it.

Again, don't want to tighten it up too much.

And use sealant on the threads as well.

Remember when I said oil runs in the line?  Well, here it is!  (Blue arrow points to the oil line).

You can see there are no leaks.  The hose has a fairly thick wall, so it's unlikely it will ever leak along its length, and there aren't any places where it makes a tight bend or contacts something sharp which might cut or abrade it.

Also, it's not hot at all - by the time it travels through the hose it cools down.

When the engine is off, the oil goes back down into the engine.

Crazy, huh?

Generally speaking, main difference between this mechanical gauge and an electrical one is accuracy and reliability.  An electrical gauge relies on a sensor which may not be accurate, lose its accuracy over time, or fail entirely.

With a mechanical gauge, we eliminate the sensor, and the gauge itself is reading the pressure directly.

Trollhättan, we have oil pressure!

The car was starting to warm up at this point.  From cold, the pressure is about 60-62 psi.  It drops to about 20 psi at hot idle.


Post a Comment 2 comments:

  • Jamesandrewberg said...
    July 4, 2016 at 10:38 AM
    Hello. I've found a number of your Saab 900 posts to be very helpful in my '86 restoration project. Are all of your Saab-related posts collected in one place on your site? The above link to "Saab c900" doesn't seem to have all of them. Thanks and keep up the good work!
  • Yr Fthfl Blggr said...
    July 6, 2016 at 9:45 PM
    Thanks for the kind words.

    There are 31 posts that I tagged with SAAB c900. They are all showing up under that heading as far as I can tell.

    Those posts display 10 to a page, so it may be that you're only seeing 10? If you go to the bottom of the page and click "Older Posts," you'll be able to page though all of them.

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