T3 oil pressure warning

[bartus81]

Hi,

I own a T3 which I try to keep in good working conditin. For me this means that each year I fix or repair something 'big' apart from the regular maintenance. The bike has high mileage, so there is/was enough to do.
One of the first bigger things that I undertook was changing the cylinders. It had the old chrome-lining cylinders and especially when hot the oil light would blip when idling. Which I attributed to the worn cylinders.
This upgrade was fantastic in terms of performance and feel. But the oil warning light kept blinking when hot. I replaced the oil pressure valve at this point, also without succes.

In the next year I replaced the chain and chain tensioner, and while at, it the oil pump. I also fitted an upgraded oil relief valve from HMB guzzi in Germany. This was very educational, and in terms of the chain and chain tensioner also useful. But again it did not resolve the oil light blinking when idling hot. This year I replaced the rocker arm spindles with an upgrade set to minimize any oil pressure loss there. Again a useful upgrade from a maintenance perspective. But it didn't help the oil light blinking.

The bike runs fine and does not consume much oil. There is some small sweating around the carter and occasionaly a drop of oil from the bell housing (that would be de next project i guess). But I can't help but wondering where the bike would lose oil pressure.

Do you guys have any ideas or tips?

[guzzisteve]

It could be something in wiring grounding the light or visa-versa, worth checking. If all fails put a gauge on it, that will tell you.

[bmc5733946]

Check that idle speed is above 1000 rpm preferably between 1100 and 1200 rpm. Low idle speeds are hard on Guzzis to much crank jump shakes the clutch hub etc. causing premature wear. It ain't no Harley and shouldn't idle like one!

Brian

[wirespokes]

It's common for the oil pressure senders to fail. But you've already replaced yours, so it aint that.

How many miles on the bike?

Out of curiosity, how did your old original cylinders look? Was the chrome flaking?

Normally, low pressure would either be the pump or main bearings.

What oil are you running?

[moto]

One common problem, I understand, is a crack or break in the gasket between the oil pan and the crankcase where the feed to the oil filter passes through. The best bet is to replace the original thin gasket with a newer, thicker one of a superior material that I have trouble characterizing. Cost twice as much but still cheap. w widely available for example at MG Cycle.

[bartus81]

Thank you all for such quick replies!
@moto The gasket has been changed a couple of times because of oil changes etc. So a break is unlikely I think.

@wirespokes: In fact I replaced the sensor twice, since at one point I forgot I already did it once :). The original cylinders where worn but not flaking. The difference between top (where the piston rings don't reach) and the rest of the barrel was quite obvious. The bike has 100.000+ km (so 62.000+ miles). The main bearings where deemed OK a couple of years ago (and I don't ride much). het rear seal was replaced then. But as I said, there is a little seeping from the bellhouse. I am running 20w40 oil at the moment, up from 10w40 usually. This made no noticeable difference (accept when cold cranking this winter).

@brian: agreed! Idle speed is around 1100 rpm. It will also invariably stall in cold weather otherwise

@steve: The wiring loom is quite new from the great Greg Bender, but I'll check just to be sure

What I have been wondering is if a blockage in the carter oil passages could lead to reduced oil pressure. I am not sure how the oil passages through the engine are routed.

[acogoff]

     As others have suggested plumb up a temporary mechanical oil pressure gauge. then you will know what is going on.
    And never assume that just because a sending unit is new that it is any good.
     My T3 runs somewhere between 40 to 50 psi.

[John A]

After being disappointed with the replacement oil pressure switches, I researched the pressures on switches at the auto parts store and found one that matched. I think it was for a slant six and I made a thread adapter. This was last century when metric switches were not all that common. Now you can get an automotive switch with the right threads on it . I used to have an oil pressure gauge but decided it took too much attention away from attention to not crashing so a reliable “replace bearings “ light is what I prefer. A temporary gauge is a good idea.

[Kiwi_Roy]

It's common for the oil pressure senders to fail. But you've already replaced yours, so it aint that.

How many miles on the bike?

Out of curiosity, how did your old original cylinders look? Was the chrome flaking?

Normally, low pressure would either be the pump or main bearings.

What oil are you running?

I spent most of my working life in industrial instrumentation so I know what a pressure switch should be like
These automotive switches are C--- The movement in the measuring element is microscopic.
It's little wonder they are unreliable.

Just check the wire is attached, unplug it and the light must go out.
Consider adding a pressure gauge 0 - 100 psi it will operate ~60 psi

[John A]

I spent most of my working life in industrial instrumentation so I know what a pressure switch should be like
These automotive switches are C--- The movement in the measuring element is microscopic.
It's little wonder they are unreliable.

Just check the wire is attached, unplug it and the light must go out.
Consider adding a pressure gauge 0 - 100 psi it will operate ~60 psi

I maintained German MBB  helicopters and the transmission oil pressure switches were a problem as were the oil pressure transmitters. The engine transmitters and switches were fine.

[moto]

... I used to have an oil pressure gauge but decided it took too much attention away from attention to not crashing so a reliable “replace bearings “ light is what I prefer. A temporary gauge is a good idea.

Agreed.

To Bartus81, the OP: Your problem has nothing to do with your cylinders or pistons. High-pressure oil is escaping to the sump through the worn bearings at a rate that worries you when the oil pressure light comes on. All high mileage engines eventually show this because they all wear out their bearings over time.

When that light stays on at running speeds above idle you have a problem, and the light has functioned properly as a "replace bearings" warning, as JohnA memorably put it. But you only have a light at idle, which is not uncommon and is not likely to result in damage. Raising the idle to 1100 may fix the light coming on (there is always an rpm value low enough to illuminate the light, by the nature of the pump.)

I emphatically agree that the distraction of monitoring extra gauges is dangerous. Idiot lights are good for everyone since they prevent this.

By the way, since I am not a native English speaker (I grew up in America) it took some googling to find out that "the carter" means "the rocker box") in our vernacular.

I hope this makes sense to you. I recommend you not worry much about an oil light at very low rpm, so long as it goes out when above idle. But I'm no expert.

P.S. I applaud your systematic approach to maintenance, and the clarity of your descriptions.

[bartus81]

@moto: Thanks for the clear explanation. I will still check the oil pressure one of these days, but with a less worried heart :).
I am also not a native English speaker (Dutchie). Where I said carter I should have said crankcase. I was curious if blockage in one of the passages around the oil filter in the crankcase could lead to low pressure at the pressulre sensor.

Anyways, this winter's overhaul is likely going to be main bearings and rear seal. Should also fix the seeping from the bellhousing, but not a job I am looking forward to.

[moto]

@moto: Thanks for the clear explanation.
... I was curious if blockage in one of the passages around the oil filter in the crankcase could lead to low pressure at the pressulre sensor.

This is plausible, but I don't think it's correct. The lubrication system is like human circulatory system where a blockage in arteries near the heart can be detected by a blood pressure cuff around the arm, far away. The pressure stays the same on either side of a partial blockage, and rises on both sides if it is serious. This is an example of Pascal's Law, one of the three or four scientific rules I command. The flow is reduced, but the pressure rises everywhere, just as in the case of a patient with high blood pressure.

[Antietam Classic Cycle]

One could always install a Murphy gauge which has a built in adjustable switch.

https://www.partdeal.com/murphy-0-100-psi-mechanical-pressure-swichgage-2-in-with-fs-contact-plated-steel-20p-f-100.html

Installation ideas: https://www.thisoldtractor.com/moto_guzzi_loopframe_oil_pressure_gauge.html#my_final_set_up

[moto]

Great gauge and installation suggestions.

Another possibility is to use a gauge that connects to a sender by wires.

Here is a VDO one I used a long time ago on a Japanese motorcycle:

https://vehiclecontrols.com/shopping/shop700/products1/1293-350-040-vdo-oil-pressure-gauge-electrical-80-psi-cockpit/#&gid=1&pid=1





It and the sender are available pretty cheap on that website. The sender triggers the idiot light at 6 +/- 2 psi. Worked fine, and is illuminated if you want to see it at night.

I will send my pair gratis to a forum member for the cost of shipping. In the US shipping is free if a donation is made to Wildguzzi.  Send a PM.

[Tom H]

You can also do this so you have the idiot light and an electric gauge. The adapter is from a BMW car IIRR, can look it up if needed.





Tom