Oil Pressure Gauge

[CJH]

I've got an oil cooler that I'm planning to mount in front of my radiator. So since I'll have oil hose running to the front of the van, is this a good place to tee-off a wet oil pressure gauge? Is the oil pressure the same throughout the system, or must the gauge feed come from one of the pressure sender locations? Do these wet gauges use a hose or a rigid (copper?) pipe?

[HarryMann]

Ahhhh!
What engine??????
There will be pressure losses in the system depending on flow rate, orifices and distance.
However that's complicated... and not that relevant.

There are two places most used by VW and others. The filter housing and up at the head for the camshaft/ valve lube flow.

Not totally sure wet/dry ? Pressure is pressure

[CJH]

It'll be a 2.1DJ (under a carb and an early DG cooling system). The oil cooler will be fed from a thermostatic sandwich plate between the filter and the engine block. I believe the normal place to take a wet pressure gauge feed is via a t-piece in either of the sender holes, but then I'd have to run pipework from there to the dash if I want a wet gauge (which apparently is the way to go for best accuracy).

It just seemed like a way to avoid extra oil-filled pipework if I could tap into the cooler circuit. My first concern was whether the pressure reading would be accurate at the end of a long rubber hose, but it's just occurred to me that I wouldn't get any reading at all until the thermostatic sandwich plate opened. So maybe not such a good place after all.

[HarryMann]

Abs. Accuracy is not that important. Relative/Comparative values are what you want any quality sender unit will give you repeatability if the voltage is consistent (e.g. from an otherwise unaffected source, not a lighting circuit takeoff!)

So do that and running a wire to the cab a lot easier and much safer than an oil line... a lot less messier too.

[CJH]

Thanks Harry

I must admit I'm much more confident about running a wire from a sender than I am about running an oil line to the dashboard. Any advice on which senders are considered most accurate?

Before I abandon the wet gauge idea though, I've been trying to get my head around how the sandwich plate works, and I'm fairly sure at least one of its two outputs is fully open to the oil pressure in the filter circuit, even when its thermostat is closed, so in fact either union at the front will see some oil pressure at all times. It feels like it might not be the most accurate place to take a feed though, since the rubber hoses to that point will be about 4m long, and then there's a potential fluctuation due to the sandwich plate opening and closing. I'd welcome any comments on this. How much does oil pressure vary depending on where in the engine you measure it?

[itchyfeet]

I'd say the most important place to know the pressure is at the engine, no room for doudt then.

[CJH]

*Good question - I don't know. It's the oil that's going through the filter, so wherever that is in the circuit.

I think you're right about measuring at the engine though. I'll drop the idea of using the cooler circuit. In general, do wet gauges use rigid pipework? I can imagine that the 'give' in a rubber hose might give a false pressure reading.

In fact, continuing that argument and applying it to my cooler hoses, if a rubber hose 'gives', would that have the effect of lowering the overall pressure in the oil circuit? If so, maybe running a couple of long lengths of hydraulic hose to my front-mounted cooler isn't a good idea? Or is hydraulic hose special in that it doesn't 'give'?

* E D I T: This made more sense before you edited the question from your post!

[itchyfeet]

Yeh sorry, the question sounded stupid so I deleted if but you were too quick.
Interested to see oil flow diagram.

[MGP]

Currently fitting my oil cooler so I will throw my thoughts in.

The sandwich plate ports to the cooler are always open regardless of thermostat position it relys on the resistance of the cooler to stop flow through it.

Hydraulic pipes will expand slightly when under pressure however the hose in front of me has a burst pressure of 1200 bar and a working pressure of 300 bar so I wouldnt worry about that however, most hydraulic hose and in fact most hoses supplied as oil cooler hose has a max working temp of about 120 degrees which I personally think is a little to close to the working temperature of the oil pre cooler.
I decided on using a ptfe hose with a stainless overbraid as its max temp something like 200 degrees.

Temperature aside another consideration is hydraulic hose is designed for carrying clean oil the oil in an engine is contaminated with all sorts and is acidic.

Lastly VW fitted oil to air coolers to the early golf gti's they used the ptfe braided pipe.

[AdrianC]

How much does oil pressure vary depending on where in the engine you measure it?

Quite a lot. If you take it on a return back to the sump, there's likely to be next-to-no-pressure, because there's nothing restricting the flow.

Take it from one of the pressure switch locations. It's where VW thought the pressure best measured... You can put an extension to somewhere comfortable, then a T-piece for both light/buzzer sender and gauge sender.

Also, if you take it from the cooler pipework, not only do you not know if it's at pressure, but you'd probably want to install a thermostat to cut the cooler out when the oil's still cool. So, when that's shut, there'll be no flow at all through the pipework...

[marlinowner]

The wet gauge in my kitcar has thin nylon pipe which is easy to route, and has been problem free in 30 years, the length supplied with a gauge wouldn't be enough for running from back to front though.

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[CJH]

The sandwich plate ports to the cooler are always open regardless of thermostat position it relys on the resistance of the cooler to stop flow through it.

Thank you - good advice about the hose. I was a bit concerned about the spec of standard hose when I first started looking into what I was going to buy.

Re your comment about the sandwich plate ports - mine's a thermostatic version, so I think one side is closed until it gets up to temperature.

Take it from one of the pressure switch locations. It's where VW thought the pressure best measured... You can put an extension to somewhere comfortable, then a T-piece for both light/buzzer sender and gauge sender.

I think this is the best plan.

Also, if you take it from the cooler pipework, not only do you not know if it's at pressure, but you'd probably want to install a thermostat to cut the cooler out when the oil's still cool. So, when that's shut, there'll be no flow at all through the pipework...

Yes, that's what the thermostatic sandwich plate should do, but I'm fairly sure one side is alwys open so therefore the whole circuit could be pressurised even when there's no flow. I guess it depends whether it's the flow or return side that is controlled by the thermostat. I need to study how it works in relation to the oil flow diagram to be sure, but it's academic now I think.

[CJH]

The wet gauge in my kitcar has thin nylon pipe which is easy to route, and has been problem free in 30 years, the length supplied with a gauge wouldn't be enough for running from back to front though.

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Thank you - better than rubber and easier to terminate than copper or cunifer. Seems ideal.

[what2do]

Is it ok to install a wet gauge in the cabin area? I wouldn't like to be upfront if the union on the gauge were to ' give up', that's a lot of hit oil at pressure to deal with!

I've only ever gutted wet gauges on agricultural machines and they're always located externally for safety reasons.

[MGP]

Mocal thermostatic plate.


Thermostat closes this port when up to temp forcing oil through cooler
.

Personally I would locate the gauge take off as far from the pump on the pressure side as possible because thats where any reading is more meaningful. Remember that pressure measurement is measuring resistance to flow so having good preasure at the pump does not mean that all parts of the enging are getting adequate supply.

Hope that makes sense when it comes to the written word im a bit retarded.