(11/5/2013) Ever since my ride to Key West last year, I've noticed that my oil pressure gauge has read much lower than the 30 psi (or thereabouts) I'm supposed to have at normal operating engine speed. The first question to ask, of course, is my oil low? Well, it was a little actually when I checked in Key Largo. But it took only a quart, which was not nearly enough to explain why the needle was falling to practically to zero at times.
Last summer, after I got back from Florida, I asked a couple of friendly mechanics about this. They suggested that because I was using synthetic oil (Amsoil) the pressure was reading so low because even for 20W50, it got really thin when hot. No, I wasn't buying that explanation.
The pressure/pressure reading was too low for one of two reasons: (1) the oil pump wasn't doing its job, or (2) the gauge was wrong. Possibility one was scary and potentially very expensive, but less likely. Jimmy Winters had my lower engine torn apart just a few years ago and said the oil pump looked fine.
I decided to start with the gauge. Here there were three possible causes of a faulty reading:
- malfunctioning gauge (shown in the photo; HD part no. 75032-99B);
- short in the wire to the oil pressure sender unit; or
- malfunctioning sender unit (HD part no. 74438-99A).
Given that my oil temperature gauge was so easily affected by rain, I decided to replace the oil pressure gauge first. As usual, I went over to my friend Mike Russo's to perform the work, which turned out to be very fortunate because we found the use of 10-inch needle nose plyers very helpful, and I don't own plyers that long. After exceeding our patience several times, we managed to get the old gauge out and the new one installed.
Disappointment ensued as the new gauge seemed to register only slightly higher readings than the old one. I then concluded it must be the sender unit. As soon as I got home, I logged onto eBay and purchased a new oil pressure sender unit.
How hard can it be to replace? You can see the pressure sender unit mounted on the right front of the engine. There it is. I even found a very helpful video on YouTube: http://www.youtube.com/watch?v=jmz12jw6W9Y. As usual, with a Harley, it's only easy if you have the right tool(s). A socket won't work, nor will an open end wrench. The maintenance manual calls for a 1-1/16" crow foot. And, friend, that is your only real option. Here's the problem though: most crow foot sets--especially for a 3/8' drive ratchet--go up to 1". I've now been outbid multiple times for single 1-1/16" crow foot attachments. Seems others have my problem too!
The new sender unit arrived in the mail, but I had no way to put it on. Turns out that's OK. The gauge now seems to be correctly displaying the oil pressure. I guess it just needed time to acclimate to the bike. So, let me know if you need a Harley-Davidson oil pressure sender unit for the touring models. I've now got a spare.
I also now have a new 1/2" drive ratchet set with a 1-1/16" deep socket that I now know will not fit past the frame onto the oil pressure sender unit. C'est la vie!
Next up: the voltage gauge
And now my voltage gauge is flaking out. I think we may have dinged a wire on it when we were replacing the oil pressure gauge. At first I thought my stator might be going again, but the needle jumped too fast from 10 to 14 volts for that to be likely. I've had my stator burn out and once that happens, it's hard to get the voltage up past 12V and then 11V and then 10V, etc. It's a gradual process of decline.
I already can't wait for winter to be over!
-The Long Rider
Michael A. Uhl