Home
What's new
Latest activity
Authors
Store
Latest reviews
Search products
Forums
New posts
Search forums
What's new
New posts
New listings
New products
New profile posts
Latest activity
Members
Current visitors
New profile posts
Search profile posts
Log in
Register
Cart
Cart
Loading…
What's new
Search
Search
Search titles only
By:
New posts
Search forums
Search titles only
By:
Menu
Log in
Register
Navigation
Install the app
Install
More options
Change style
Contact us
Close Menu
Forums
Cobra Forums
New Edge Cobras
99 cobra oil pressure at idle?
JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding.
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an
alternative browser
.
Reply to thread
Message
<blockquote data-quote="52merc" data-source="post: 15997747" data-attributes="member: 197"><p>Factory hypereutactic pistons do not change much in width as temperature changes (compared to conventional aluminum alloy pistons) and are close tolerance fit at the factory. There were 3 different piston ranges that were colour coded Red, Blue, and Yellow. Cylinder bores were measured and the pistons were then matched up with the cylinders to obtain a <strong>maximum</strong> Piston-to-Bore clearance of 0.026 mm [0.0010"]. This reduces cold start piston slap and oil consumption. This helped to get the low-emission rating that these engines had. One of the reasons the factory oil was 5W-20 was to reduce the likelihood of scoring the piston skirt during cold start. Although a 5W-40 has the same SAE rating, it doesn't necessarily mean that the viscosity is the same at all low temperatures. If you live where it gets cold, and drive your car all year long, be careful not to go too high on the W side.</p><p></p><p>These engines also have a problem if you run at high rpm for any extended time, of oil collecting up in the heads and not returning to the sump quickly enough. Using a higher weight oil may require running the oil level on the higher side to limit oil pump starvation, especially if you run extended high revs before full operating temperature is reached.</p><p></p><p>Crankshaft bearings are also a tight fit from the factory. Main bearing clearance is 0.025 mm to a maximum of 0.050 mm [0.00098-0.00197"] and rod bearing clearance is 0.027-0.069 mm [0.00106-0.0027"]. The reason these are so tight is that aluminum expands more with temperature than steel. At operating temperature the bearing clearance is actually more.</p><p></p><p>I'm not saying 5W-40 is bad, and I'm not saying other oils are bad. I'm just explaining some of the reasons the factory spec was the 5W-20 semi-synthetic and some things to consider before choosing your oil.</p></blockquote><p></p>
[QUOTE="52merc, post: 15997747, member: 197"] Factory hypereutactic pistons do not change much in width as temperature changes (compared to conventional aluminum alloy pistons) and are close tolerance fit at the factory. There were 3 different piston ranges that were colour coded Red, Blue, and Yellow. Cylinder bores were measured and the pistons were then matched up with the cylinders to obtain a [b]maximum[/b] Piston-to-Bore clearance of 0.026 mm [0.0010"]. This reduces cold start piston slap and oil consumption. This helped to get the low-emission rating that these engines had. One of the reasons the factory oil was 5W-20 was to reduce the likelihood of scoring the piston skirt during cold start. Although a 5W-40 has the same SAE rating, it doesn't necessarily mean that the viscosity is the same at all low temperatures. If you live where it gets cold, and drive your car all year long, be careful not to go too high on the W side. These engines also have a problem if you run at high rpm for any extended time, of oil collecting up in the heads and not returning to the sump quickly enough. Using a higher weight oil may require running the oil level on the higher side to limit oil pump starvation, especially if you run extended high revs before full operating temperature is reached. Crankshaft bearings are also a tight fit from the factory. Main bearing clearance is 0.025 mm to a maximum of 0.050 mm [0.00098-0.00197"] and rod bearing clearance is 0.027-0.069 mm [0.00106-0.0027"]. The reason these are so tight is that aluminum expands more with temperature than steel. At operating temperature the bearing clearance is actually more. I'm not saying 5W-40 is bad, and I'm not saying other oils are bad. I'm just explaining some of the reasons the factory spec was the 5W-20 semi-synthetic and some things to consider before choosing your oil. [/QUOTE]
Insert quotes…
Verification
Post reply
Forums
Cobra Forums
New Edge Cobras
99 cobra oil pressure at idle?
Top