Occasional cold start noise

[PaulQ]

9 hours ago, Cheddar Bob said:

As oil warms it becomes more viscous this requiring more pressure from the pump or a reduction in pressure will occur

If oil becomes more viscous when it warms, why is the pressure higher when the oil is cold.? 

[Cheddar Bob]

40 minutes ago, PaulQ said:

If oil becomes more viscous when it warms, why is the pressure higher when the oil is cold.? 

It's called KV or(kinematic velocity)

Think of 1kv as water. 1000 as honey. 

As the temperature increases, engine oil will shear and become more viscous. The oil pump will be designed to maximise flow rate on cold start performance and as the KV decreases due to shear the pressure will decrease. 

The oil pump system is not a completely sealed system, so you need to account for air ingress, cubic capacity throughout the system. There are of course many pressurised compartments within the lubrication network of an engine. 

 

If you are comparing this to say a coolant system, water doesn't shear so when it heats up, it expands in a sealed system, thus increasing pressure. 

Try putting 1kg of of honey in a 5cm tube with a 1cm hole at the bottom and an equivalent piston at the top. The force you need to push that honey through the 1cm will be many times less when warm and an incredible amount less when it is hot. 

As the KV becomes close to water, so 1 the pressure will reduce. 

 

Think high blood pressure tablets, they contain aspirin to thin the blood. 

 

Hope this answers your question. 

 

[Nobbie]

33 minutes ago, Cheddar Bob said:

It's called KV or(kinematic velocity)

Think of 1kv as water. 1000 as honey. 

As the temperature increases, engine oil will shear and become more viscous. The oil pump will be designed to maximise flow rate on cold start performance and as the KV decreases due to shear the pressure will decrease. 

The oil pump system is not a completely sealed system, so you need to account for air ingress, cubic capacity throughout the system. There are of course many pressurised compartments within the lubrication network of an engine. 

 

If you are comparing this to say a coolant system, water doesn't shear so when it heats up, it expands in a sealed system, thus increasing pressure. 

Try putting 1kg of of honey in a 5cm tube with a 1cm hole at the bottom and an equivalent piston at the top. The force you need to push that honey through the 1cm will be many times less when warm and an incredible amount less when it is hot. 

As the KV becomes close to water, so 1 the pressure will reduce. 

 

Think high blood pressure tablets, they contain aspirin to thin the blood. 

 

Hope this answers your question. 

 

Maybe I’m missing something, but you keep saying that oil viscosity increases with temperature. In my mind that means the oil getting thicker which is not true from my experience.

[PaulQ]

1 hour ago, Cheddar Bob said:

It's called KV or(kinematic velocity)

Think of 1kv as water. 1000 as honey. 

As the temperature increases, engine oil will shear and become more viscous. The oil pump will be designed to maximise flow rate on cold start performance and as the KV decreases due to shear the pressure will decrease. 

So your saying shear makes the oil more viscous as the temperature increases, yet as the viscosity decreases due to shear the pressure will drop.? 

Makes no sense whatsoever. 

Whats kinematic velocity.? 

[Cheddar Bob]

40 minutes ago, PaulQ said:

So your saying shear makes the oil more viscous as the temperature increases, yet as the viscosity decreases due to shear the pressure will drop.? 

Makes no sense whatsoever. 

Whats kinematic velocity.? 

I'd politely ask you to read my post again. 

Search Kelvin, then search kinematic velocity and whilst your at it centistokes. 

This is why I enjoy reading lubricant topics on forums. They always turn into some for of argument, as politely everyone likes to think they know better. 

You are both welcome to come to my work at any point if you would like to discuss this in person. I'm based in Gloucester most days. 👍

[Cheddar Bob]

Here's a quick YouTube video for you 

👍

[Cheddar Bob]

1 hour ago, Nobbie said:

Maybe I’m missing something, but you keep saying that oil viscosity increases with temperature. In my mind that means the oil getting thicker which is not true from my experience.

Sorry nobbie I've just read my posts again and I don't think I've made that connection as you've took it but , if you look at viscosity increasing as in the number on the lubricant gets higher, eg a 30 to 60 then yes you would be confused. 

When a viscosity increases the numbers get smaller refering to the fluidity of the product. 

If you refer to the viscosity decreasing then the numbers get higher. 

Viscous = fluidity so more viscous more fluid less viscous more solid

 

[PaulQ]

4 minutes ago, Cheddar Bob said:

I'd politely ask you to read my post again. 

Search Kelvin, then search kinematic velocity and whilst your at it centistokes. 

This is why I enjoy reading lubricant topics on forums. They always turn into some for of argument, as politely everyone likes to think they know better. 

You are both welcome to come to my work at any point if you would like to discuss this in person. I'm based in Gloucester most days. 👍

It's kinematic VISCOSITY not velocity. 

I don't for one minute think I know better then  you, but if post confusing information then expect to get questioned about it

 

[Cheddar Bob]

3 minutes ago, PaulQ said:

It's kinematic VISCOSITY not velocity. 

I don't for one minute think I know better then  you, but if post confusing information then expect to get questioned about it

 

Fook I'm using a mobile phone with Swype  I didn't even realise that's how it was written. No issue with questions at all, please feel free to call anything out I say. In my experience these conversations never end well 

🙈

Yes you are 100% correct with that and I'm going to print this off for my colleagues on Monday. 😶

[Nobbie]

38 minutes ago, Cheddar Bob said:

Sorry nobbie I've just read my posts again and I don't think I've made that connection as you've took it but , if you look at viscosity increasing as in the number on the lubricant gets higher, eg a 30 to 60 then yes you would be confused. 

When a viscosity increases the numbers get smaller refering to the fluidity of the product. 

If you refer to the viscosity decreasing then the numbers get higher. 

Viscous = fluidity so more viscous more fluid less viscous more solid

 

OK, I see it’s the difference between how the word viscosity is generally discussed and it’s specific scientific usage. I can see why you get problems discussing it on forums.

[Cheddar Bob]

48 minutes ago, Nobbie said:

OK, I see it’s the difference between how the word viscosity is generally discussed and it’s specific scientific usage. I can see why you get problems discussing it on forums.

All the time.