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Oil Warning Light - for the 4-cylinder engine ?


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On 5/13/2022 at 10:51 PM, Hamish said:

When I fitted mine I thought of a a buzzer and light. It can be quite a busy time on a sprint.

but then I realised that it would be damned annoying to have the buzz every time the ignition was on and engine not running.

and I wouldn’t be able to hear the elec fuel pump tone change when the carbs are full.

So, Hamish, you have an electric fuel pump.    Did you consider wiring it’s relay via the oil pressure switch so if the oil pressure fails the pump cuts off?    I had a Metro Turbo with that arrangement as fitted standard.

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2 hours ago, BlueTR3A-5EKT said:

So, Hamish, you have an electric fuel pump.    Did you consider wiring it’s relay via the oil pressure switch so if the oil pressure fails the pump cuts off?    I had a Metro Turbo with that arrangement as fitted standard.

Starting would be delayed if float bowls were not full, as the pump would not start until pressure had built up. maybe that's a good thing ?

Bob

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3 hours ago, BlueTR3A-5EKT said:

So, Hamish, you have an electric fuel pump.    Did you consider wiring it’s relay via the oil pressure switch so if the oil pressure fails the pump cuts off?    I had a Metro Turbo with that arrangement as fitted standard.

No didn’t go that route. As Bob says not sure how the car would start as I let the fuel pump run with ignition before starting. 
I do have an impact cut out switch that’s  now within reach in the driver compartment.

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1 hour ago, Lebro said:

maybe that's a good thing ?

Surely not ..for the starter motor, or the battery and its wiring, especially if the car is often used for short runs. 

Nor, I suspect, is it good for the engine which relies on oil-splash to lubricate the bores and many other interacting components.

As I understand it..  engine lubrication a balance of both pressure and  flow rate.  An engine which starts easily and has a good oil pump will pressurise the oil within all  its galleries almost instantly ..while the engine is under very little load. From the rate of spin / centrifuge - there will be good oil splash (intensive spray) and subsequent return flow of oil (over cam-followers for example).  Whereas an engine that is slowly turned (..relatively speaking) will not offer the same magnitude of pressure wave throughout its oil galleries, because any localised losses (manufacturing tolerances & wear) will be to the detriment of oil pressure further along a circulation route.  It's oil splash will be weak, and the smaller streams of returning oil will likely be evident as streaks rather than as a wash.  

Of course, the counter argument is that with combustion loads - the started engine does have higher loads on its big end and main bearings.  I think it is a question for the engine's designer.  As very likely different engine designs will have a different answer.

Pete

 

Edited by Bfg
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6 hours ago, Lebro said:

 

Starting would be delayed if float bowls were not full, as the pump would not start until pressure had built up. maybe that's a good thing ?

Bob

You wire an override circuit from starter push switch/relay to the pump.  
 Press the starter and the pump runs, when engine catches you release the starter push and the oil pressure of the engine maintains the pump relay as energised.

 

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That arrangement is in use on lots of cars, it did cause some head scratching on an XJ years ago when the switch in the oil gallery failed, you couldnt tell the pumps werent working as theyre in tank so you couldnt hear them.

Stuart.

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I’ve never believed that any device that automatically stops the engine running while the car is moving, either by switching off the fuel pump or switching off the power to the coil, is a safe idea.

I just imagine being in the outside lane on the M25 or just going into a blind bend on a country road and having the engine stop.

Personally I’d rather have to rebuild an engine than have the possibility of an HGV pushing me down the road.

Charlie.

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^ been there on a very busy motorway section with no hard shoulder - when 'the modern' suddenly went into limp mode ..caused by a faulty sensor on the throttle pedal.  It's not an experience I'd choose to repeat. 

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  • 2 months later...

Hi Pete,

thank you for starting this thread, I remembered and browsed it,

currently knitting on a oil warning light because of the worn engine of a member of the German forum.

Found some good ideas here, the adapter I make myself.

Currently I'm not shure what pressure switch I should buy, I go fancy with 1.5 bar...

Ciao, Marco

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7 hours ago, Z320 said:

Hi Pete,

thank you for starting this thread, I remembered and browsed it,

currently knitting on a oil warning light because of the worn engine of a member of the German forum.

Found some good ideas here, the adapter I make myself.

Currently I'm not shure what pressure switch I should buy, I go fancy with 1.5 bar...

Ciao, Marco

With a worn engine and thin hot oil the light may flash at 1.5 bar (22 psi) when at low tickover sitting in traffic.

Just my thoughts.

Peter W

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Hi Peter, thank you for your thoughts!

I ask myself what is the lowest pressure to accept, means the engine gets no damage.

If it works without damage running on 1.5 bar I fit a 1.0 bar sensor.....

The TR6 has a oil warning light, what pressure is the according sensor, please.

Rimmer offers a 20 PSI and a 5 PSI. This is a "nice" difference.

Ciao, Marco

Edited by Z320
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Marco you can get adjustable versions.  That I guess type could set to your cars gauge ? At “just under normal hot tickover” to stop the flicker in normal use  

https://www.demon-tweeks.com/longacre-universal-low-oil-pressure-switch-346246/?sku=LON902540&istCompanyId=a2904180-3a7d-4e56-b876-cf81c9512180&istFeedId=6fbc4b04-fd28-4ce1-8513-835c8f118690&istItemId=wptpltawi&istBid=t&gclid=EAIaIQobChMIhtqQ9f2z-QIVPJBoCR26zQiCEAQYASABEgKxWPD_BwE&gclsrc=aw.ds

 

this is just one source to show availability  

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Good morning Hanish,

thank you for this idea, but sadly i don’t own a 1/8 NPT tap but a M10x1,

which is the common thread for not adjustable oil pressure switches.

Ciao, Marco 

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Is it a problem that the light may flash at tickover?

Not really an irritation and it does show that the switch is doing its job.

(And a reminder that maybe it's time to rebuild the engine :()

 

Charlie.

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I don't know what the pressure switch is set to on Katie's,  it is adjustable ..as supplied, but I haven't adjusted it.  It is provided by TR Enterprise < here >  ..presently Out Of Stock.  This switch is, I believe, the same as that supplied by Merlin Motorsports < here > who claim it to be pre-set at 35psi (2.4 bar). 

Whatever Katie's  is set to (and these switches are adjustable), it goes out immediately upon starting the car.  The lowest I've seen on the car's (original and not checked for accuracy) oil pressure gauge - when the car was used around town in really hot weather was about 45psi (3.1 bar) ..and I saw no flickering of the warning light.

< here > is the way I fitted this kit into Katie, taking the (switched power) feed from the fuse box to the lamp. That lamp of course illuminates when the lamp's electrical circuit (via the wire to the switch) is earthed by that switch. 

Pete 

 

 

Edited by Bfg
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1 hour ago, Z320 said:

Good morning Hanish,

thank you for this idea, but sadly i don’t own a 1/8 NPT tap but a M10x1,

which is the common thread for not adjustable oil pressure switches.

Ciao, Marco 

£6.00 buys one. Plus whatever tax and postage.

https://www.tracytools.com/taps-and-dies/npt-taps-dies/1-8-x-27-tpi-npt

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Hi Peter,

thank you, could you also guide me to a oil pressure „without pressure open“ switch for another project,

not the commen „wihhout pressure closed“ switch, please?

Ciao, Marco 

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20psi is the more usual setting for the light to come on. I think the TR5/6 ones are set at that.

Stuart.

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39 minutes ago, Z320 said:

could you also guide me to a oil pressure „without pressure open“ switch for another project

You can change the switching sense of the standard cheap pressure switch using a transistor Marco, like this:  

psw.jpg.cc607bb39fd04f1cf56de6a94882a586.jpg

The transistor is conducting at all times while the switch is open and turns off when the switch makes. 

 

 

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Hi Rob,

thank you very much for your effort for explaining and making the sketch, this is good to know and I'll try to keep that in mind.

I found a oil pressure switch for 14 Euro inkl. shipping (German car) with 3 terminals, one normally closed to the ground for the warning light.

And the other 2 (not grounded) normally opened to switch my Pierburg anti run on valves automaticly.

The warning light is already in a good position,

I wanted small effort and no drilling, so I fixed it with a simple 2.5 mm wire like a goose neck from below the dashboard.

6js4buaoww2dJQ0rPxTDpU-IAaC4sPDOPGXGoE0a

Looks a bit like an alian?

Ciao, Marco

 

 

 

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  • 4 weeks later...

Hi,

time for an update: the oil pressure failed - on the NC terminal.

This makes me wonder, because the LED control light need only a very low current.

And on the NO terminals it also failed: because I switched 2,5 A for my Pierburg valves it did not always open again.

This is why I made this unit with an industry NO and NC switch, both adjustable from 0 - 2 bar.

bA4357NC-bC74oTRbfW-4Ee4YZ8DkuZps_rpX61b

They have been sold to switch 5A (!) each what I can't explain....indeed they can only switch 0.5 A AC and 0.2 A DC, this "fits".

So I had to add a little relay, this way it works well. Another controll LED show me the NO switch now opens properly.

  knC5L91HJUZfW51hf0nmTbgxUTASfvZubnTN3oAh

Next winter I will move the unit from "on the bulkhead" to "behind the dashboard", it look not that much "suitable" for a the car.

Ciao, Marco

 

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