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'77 GS750 Oil Light

  • Thread starter Thread starter tjhenry
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tjhenry

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I just got a '77 GS750. The oil light has been on since i got it a week ago and i've only driven it 45 or so miles to get it home. I'm changing the oil this weekend, but the oil level is fine.

I've done a little reading, and the 77's aren't equipped with the pressure sensors. Is this light just saying it has lost it's viscosity and it's time for a change or is this a more serious problem? I did read that it's a low pressure pump in a service manual, but I'm at a loss of what i should do other than changing the oil. Is it still driveable until i change the oil?:confused:

i can't find much on the subject, and I've never owned a motorcycle before, so I'm completely new at this. :confused:

Please help!
 
That is not an oil change light. That is a low oil pressure light. Do not drive it until you get it figured out. Make sure the wire is hooked up to the oil switch. if it is check oil pressure with a mechanical gauge. Let us know what you find.
 
Look on top of your engine, under the carbs for the oil pressure sensor plate. There will be a white plastic plug in the middle of a small plate held down with two screws. Check to see if there is a wire connected to the white plug - this is the oil pressure sensor. If you find the wire, take it off the plug and ground it out - the oil pressure light should go out. If it doesn't, or if the wire is not there, you found your problem. If the light goes out when grounding this wire, yet it doesn't go out when you ride the bike, you have an oil pressure problem and don't ride the bike.

Hope this helps and good luck.
 
On the 77-79, they don't have an pressure sensor. It's just three bolts holding the filter plate on.

So i basically need to change the oil no matter what and see if that fixes it? Is this due to viscosity breakdown?

Nessism said:
Look on top of your engine, under the carbs for the oil pressure sensor plate. There will be a white plastic plug in the middle of a small plate held down with two screws. Check to see if there is a wire connected to the white plug - this is the oil pressure sensor. If you find the wire, take it off the plug and ground it out - the oil pressure light should go out. If it doesn't, or if the wire is not there, you found your problem. If the light goes out when grounding this wire, yet it doesn't go out when you ride the bike, you have an oil pressure problem and don't ride the bike.

Hope this helps and good luck.
Click to expand...

are you talking about what should be on the oil filter plate in front? im' going to head out to the garage to take a quick peek.
 
Last edited:
tjhenry said:
On the 77-79, they don't have an pressure sensor. It's just three bolts holding the filter plate on.

So i basically need to change the oil no matter what and see if that fixes it? Is this due to viscosity breakdown?



are you talking about what should be on the oil filter plate in front? im' going to head out to the garage to take a quick peek.
Click to expand...
Your reading was wrong. The 77-79 and EVERY GS to my knowlege HAS an oil pressure sensor. Its NOT on the filter cover. They arent in the same place as the 80-82 750s. Its behind the cylinders, under your carbs. A while hex looking cap with a wire lead coming out of the top. IF that came disconnected, your oil pressure light will come on. If its been cut, or frayed or somehow no longer connected, your oil pressure light will come on... I dunno where you got this info, but please, for the love of your bike, dont listen or refer to this source of info ever again.
 
Gotcha, I found it in it's incredibly cramped position. Please feel like you're dealing with a complete idiot here, because you pretty much are. :oops:

I was looking through a service manual, and it says to just pull it out. is there anything clamping the wire down i may break, or is it a simple tug, unfray the wire, ground it to see if it works, and then put it back in? i wont' get to this part until tomorrow evening after work. :-k

The previous owner said it's been 3,000 miles since he changed the oil, which I'm pretty sure is very bad. Would oil break down enough after this amount of time (i'm inclined to believe years) to set off this light?
 
holy crap 3,000 miles.

whever i buy a bike the first thing i do is change the oil regardless of what the PO says, and your PO is basically telling you to change the oil.

As far as the wire goes, if the manual says so, i would follow it, but be gentle. The only gs i have is an 82 so its different.


Hope this helps
 
the 750 kicker engines are tough as nails...
i wouldnt sweat the oil light or lack of oil change.
ive busted apart maybe 20 of these engines and never seen any damage besides rust from being at the bottem of a pound.
 
Good deal, i'll change the oil first and see if the light goes off. if that doesn't work, i'll pull the wire off and start fiddling.

thanks for your help everyone, i've got more questions, and i'm glad there is a community devoted to the GS bikes, i'm pretty excited to start my motorcycle life with a bike that seems to be pretty well respected

blower-i did some research on the 750's, and figured it to be a great starter bike with amount of posts on carious forums of people saying they'd put 60-100k miles on them. i'm pretty excited, just not a good wrench, good to know they can take a lickin' and keep on tickin' :D
 
if the oil sending unit is sticking or if the connection is broken from the wire going to it...
that would make it stay on.
the only other thing is no oil pressure.
pumps dont really go bad but a pump gear could break or a couple differant things in that area...never seen it but its possible.
get it figared out/put some HD clutch springs in it and a 50 HP shot of NOS or a turbo on it...
tough engines that can take it!
 
The oil light is grounded through the sender. The oil light doesn't go on if you disconnect the sender, it goes out if it's disconnected. If the oil light is still on when you disconnect the wire from the sender, there is a short in the wire somewhere.
 
Guy said:
The oil light is grounded through the sender. The oil light doesn't go on if you disconnect the sender, it goes out if it's disconnected. If the oil light is still on when you disconnect the wire from the sender, there is a short in the wire somewhere.
Click to expand...

so it should be on?:confused:
 
Just a heads up .. on my 750... my screw on my oil pressure sensor came loose and was grounding on my pipes...each time it touched the oil light cam eon.. freaked me out... perhaps you have the same issue and the loose wire is grounding elsewhere
 
The so called sensor is not a sensor really, it’s a switch. Basically it’s just a spring loaded metal plunger that sits down over top of the main oil feed port. When there is no oil pressure the plunger sits down on the port and there is a ground path which completes the circuit for the light to illuminate. This is why the light comes on when the engine is not running. When the engine is running, oil flows up and pushes the plunger away from the port which disrupts the ground circuit and makes the light go out.
 
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