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Old 26-05-2015, 11:44   #16
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Re: Oil pressure gauge increasing with revs

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Originally Posted by JulianGullsway View Post
Hi we seem to have in increase in oil pressure when the revs are increased it normally it sits at around 40psi and have run her longer than this in the past with out issue, we are currently cruising in the Med and this happened after being under engine for nearly 15 hours at no more than 2000rpm, I use 15/40 oil which I'am thinking of changing to a thicker grade due to the water temp here. we have a Perkins 4108 and help would be very much appreciated
A slight increase in pressure relative to rpm is normal. Spikes are another matter entirely.

It sounds like you are describing an abnormal increase but not spikes or fluctuations.

Spikes in oil pressure were often an indicator of seizure back in my motorsport days. I was involved in several engine development programs that started with very short lives. 5 hours. So I'm overly familiar with this condition.

However the Perkins is a reliable beast so I'd be inclined to check my gauge first. Blockages in oil galleries through either foreign objects or carbon lumps in the vicinity of the oil pressure sender can also impact gauge readings. An oil analysis will put your mind at rest. I have them done at each change, 4-236, so i can spot any trends.

The original Perkins were designed for a straight 30 weight oil. Your 15/40 weight oil should be ideal especially for an older engine. Change it and the filter regularly.

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Old 26-05-2015, 12:07   #17
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Re: Oil pressure gauge increasing with revs

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Originally Posted by Guy View Post
I hope not many boats have a mechanical gauge with an oil "tube" going to it. The guy who lost oil pressure and had his engine seize should agree. Oil pressure gauges should probably be electrical with a sending unit. If you want a mechanical gauge it should have a proper flexible hose going to it, not a little 1/8" plastic or copper tube like a car might have. In addition to that, if you want a mechanical gauge the fitting on the engine should have a small orifice to limit oil loss if it fails.
In either case, the last bit of hose or the sending unit itself should be filled with auto trans fluid or some sort of light oil that does not coagulate.
anyone not having BOTH electrical because the fail rate is higher than mechanical , and electrical just to make sure the mechanical one aint fail--is insane.
the heart of the boat is engine. when it is sick it will complain. duh. mine did.
i had both electrical and mechanical gages on my boats engine. electrical quit first, then mechanical.
i trust mechanical gages over electrical every day, as i learned from my love of vws and sporty cars to do this. is important and allows any doubt to be assuaged immediately.

my engine books say to use 30 wt or 40 wt oil in my engine. not multigrade oil.
have fun. i trust books over forums. good luck.
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Old 26-05-2015, 14:12   #18
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Re: Oil pressure gauge increasing with revs

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Originally Posted by zeehag View Post
anyone not having BOTH electrical because the fail rate is higher than mechanical , and electrical just to make sure the mechanical one aint fail--is insane.
the heart of the boat is engine. when it is sick it will complain. duh. mine did.
i had both electrical and mechanical gages on my boats engine. electrical quit first, then mechanical.
i trust mechanical gages over electrical every day, as i learned from my love of vws and sporty cars to do this. is important and allows any doubt to be assuaged immediately.

my engine books say to use 30 wt or 40 wt oil in my engine. not multigrade oil.
have fun. i trust books over forums. good luck.
Yes-I agree! I have mech. oil press. & temp gauges & electric alarm senders for both on VP2003. I like alarms backing up gauges. / Len
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Old 26-05-2015, 14:14   #19
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Re: Oil pressure gauge increasing with revs

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As far as I know, the numbers on a grade of oil, e.g. 10/W30, 15/W40 etc., refer to the range of temperatures for which it is suited i.e. 10/W 30 for use between -10deg Centigrade and +30deg Centigrade.
These are Multigrade oils, which are designed for use all year round. They were introduced in the 1960s to replace the oils they had then, which were either Winter Grade, or Summer Grade and had to be changed seasonally.
15/W40 should be fine for use in the Med but I personally would not deviate from using the oil specified in the engine's user manual.


The numbers on a grade of oil have nothing to do with the range of temperatures for which the oil is suited. They are a measurement of the oil's viscosity (basically it's thickness or ability to flow). For a good explanation of this there are a few websites that you could review. Here's an example of one: Motor Oil Viscosity Grades Explained in Layman's Terms
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Old 26-05-2015, 14:28   #20
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Re: Oil pressure gauge increasing with revs

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Originally Posted by SpiritofGlenans View Post
As far as I know, the numbers on a grade of oil, e.g. 10/W30, 15/W40 etc., refer to the range of temperatures for which it is suited i.e. 10/W 30 for use between -10deg Centigrade and +30deg Centigrade.
These are Multigrade oils, which are designed for use all year round. They were introduced in the 1960s to replace the oils they had then, which were either Winter Grade, or Summer Grade and had to be changed seasonally.
15/W40 should be fine for use in the Med but I personally would not deviate from using the oil specified in the engine's user manual.
You have the right idea but.....

The W in 10W30,etc. used to stand for "weight"-the commonly used term for oil viscosity back in the day.
A 30W oil will thin out to the viscosity of a 10W oil,at operating temps.
A10W30 oil will have a constant 10W viscosity over it's operating temp range-ie: it's viscosity doesn't change.
This thin constant 10W viscosity allows the engine to roll over,& pump oil,at colder temps,which is extremely good for "cold" engine lubrication during the first few minutes after a "cold" start,even in the tropics.
The appropriate multigrade oil is good for all engines.
If you manual calls for 30W,you can safely use 10W30
15W40 is for hot conditions & replaces 40W
5W40 is for extreme cold Arctic starting conditions.

Cheers/ Len
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Old 26-05-2015, 15:15   #21
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Re: Oil pressure gauge increasing with revs

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Originally Posted by luciarose View Post


The numbers on a grade of oil have nothing to do with the range of temperatures for which the oil is suited. They are a measurement of the oil's viscosity (basically it's thickness or ability to flow). For a good explanation of this there are a few websites that you could review. Here's an example of one: Motor Oil Viscosity Grades Explained in Layman's Terms
I feel educated! Interesting site. Good info on synthetics. ie: not all synthetics are desirable anymore. Crooks abound!
Caveat emptor
/ Len
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Old 27-05-2015, 04:35   #22
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Re: Oil pressure gauge increasing with revs

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What are the pressures at idle and at cruising RPM, hot and cold?

IE, 4 numbers :

Idle cold
Idle hot
Cruising cold
Cruising hot

How have the pressures changed?

Without this information, no-one can help you.
Ok the oil pressure normally sits at around 35-40 psi, when she gets really hot the needle flickers a little which I would suspect, but the needle was going straight over the the other side of the gauge, yet when I power down to idle it goes back to 35-40 psi, I hope this helps, thanks for your help.....
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Old 27-05-2015, 04:37   #23
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Re: Oil pressure gauge increasing with revs

Without this information, no-one can help you.[/QUOTE]

Ok the oil pressure normally sits at around 35-40 psi, when she gets really hot the needle flickers a little which I would suspect as the oil get hotter, but the needle was going straight over the the other side of the gauge, yet when I power down to idle it goes back to 35-40 psi, I hope this helps, thanks for your help.....
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Old 27-05-2015, 07:57   #24
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Re: Oil pressure gauge increasing with revs

It's the oil pressure relief valve. It's sticking.
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Old 27-05-2015, 08:04   #25
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Re: Oil pressure gauge increasing with revs

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Posted by JulianGullsway: Ok the oil pressure normally sits at around 35-40 psi, when she gets really hot the needle flickers a little which I would suspect as the oil get hotter, but the needle was going straight over the the other side of the gauge, yet when I power down to idle it goes back to 35-40 psi, I hope this helps, thanks for your help.....
Possibly the sending unit but how hot is the engine getting? Do you have an IR temperature sensor that you can use to check what your temp. gauge is telling you? Are you noticing any steam coming out the exhaust when hot?
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Old 27-05-2015, 08:07   #26
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Re: Oil pressure gauge increasing with revs

Whoops sorry a 4108 can't produce anything above 60psi, apparently it's not possible and I think it may just be the electric sender unit, I had a spare gauge but that's working fine so we are on the hunt for a new sender, being a bit tricky as we are in San Pedro in Sardinia and we have serious language barrier....
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Old 27-05-2015, 19:15   #27
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Re: Oil pressure gauge increasing with revs

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Originally Posted by JulianGullsway View Post
Whoops sorry a 4108 can't produce anything above 60psi, apparently it's not possible and I think it may just be the electric sender unit, I had a spare gauge but that's working fine so we are on the hunt for a new sender, being a bit tricky as we are in San Pedro in Sardinia and we have serious language barrier....
I hope everything works out for you but it's not true that the 108 oil pump can only make 60psi. It's the pressure relief valve that determines the max pressure. That style oil pump could probably make 2000 psi if the relief valve would let it.
Even if you are in a foreign land, there are basicly only 2 kinds of sending units, one for pressure and one for an idiot light. Yoy could probably use a sending unit from a Fiat as long as it was for pressure and not just an on and off switch for a light. There are different resistance values for sending units but usually they are about the same.
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Old 31-05-2015, 02:50   #28
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Re: Oil pressure gauge increasing with revs

Thanks Guy, I will have a look at that, iam sure its the sender unit. When on idle it bounces straight back to 34-40psi but even when it goes crazy at 2000 rpm it still often settles back to the above pressure, fingers crossed thanks for the input!!!
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