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Engine Oil Weight

21K views 69 replies 23 participants last post by  1turbofocus 
#1 ·
I got a scolding from a member wanting to know why I would give him bad advice about running a higher then 20wt engine oil in his car

He stated after talking to many people that running higher then 20wt would "blow the seals, and the head gasket " This has to be the dumbest most moronic thing I have ever seen , engine oil blowing a head gasket ???

There is no more PSI on the seals or the head gasket with 50wt then there is with 10wt

Running 20wt oil is fine if you driving the car normal back and forth to work and to the grocery store or in the winter under extreme cold conditions , once you start modding your engine you need more protection with a higher wt oil , I run 40 in the winter and 50 in the summer but most dont have turbos and making the power I do

The engines I build I tell most to run 30or40 winter and 40or50 summer depending on there HP and what they use it for, this is my opinion/advise it does not mean this is what you have to do

I would love for the guy that told him he would have head gasket issues to post and explane

Please post your oil opinions about going to a higher WT oil for better protection

Tom
 
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#41 ·
I wonder if anyone takes into account NHRA prostocks use very light oil..............less than 20wt, infact down in the 10wt range. Granted they change oil after every pass or two.

The oems spend thousands of dollars on durability testing, if 5w-20 did not hold up, they would not use it. Yes it helps fuel economy, but it does pass the harsh testing they subject the engines to. There are a few exceptions like the Ti-VCT Ecoboost which uses 5w-30, and the Boss 302 that uses 50wt Mobil 1.

I use 5w-20 in the winter and 5w-30 in the summer, never had any issues.
 
#52 ·
Heavier oil should be run when the car ages. If you have 125K+ on the car, run 5w 30. If you just rebuilt the engine, run 5w 20. More worn out parts need better lubrication to resist further wear.
 
#53 ·
Sry to revive this old thread.

What oil would you use on a turbo Duratec forged (pistons and rods) making around 300whp? Here in my city ambient temps are around 86 to 105F most part of the year, it's very hot. I'm running a 15w40 viscosity, should I go thicker?

Thanks
 
#56 ·
I use the mobile 50 in the summer and 40 in the winter , all synthetic

The piston slap isnt from the oil and thicker oil wont correct it , you either have over heated the pistons as some point and they have collapsed ( skirts ) or the bore was done to big and the piston is slightly loose when cold and the piston swells when hot and the noise goes away

Tom
 
#57 ·
The pistons are fine, I checked the skirts diameter before installing then, same measures as new, these pistons are a little smaller than the stock ones, it has 87.42mm and stock has 87.48mm, bore is 87.50mm.
Do you use 50 oil mineral or synthetic?

Thanks Tom
 
#59 ·
Pistons collapsing-more conventional wisdom bullshit. Pistons don't collapse. They can wear of course and what they do like lightning when overheated, wear the crap out of the thrust faces as they try to stick in the bore. At that point they are trying to seize up, what 2 strokes commonly do.

Any piston going so far as to 'collapse' is borderline breaking up in pieces at any second. They don't just collapse to a point and then stop and even more so with a forging.

ALL pistons swell when hot, some are just tightly controlled, it depends on the aluminum alloy used and how much silicon in it. Straight aluminum swells at 3X the rate of an iron block, the piston structure is altered in design to control it as well as the silicon amount.

Numbers quoted there could have around .004" piston-to-wall which could possibly rattle a bit cold. A little is fine and can run forever.

I've run them at up to .008" and some rattle but the engines lasted forever. The key is matching the boresize to the aluminum alloy.

Single weight oil can run fine in those Brazilian temps, I run 30 and 40 (summer) straight here in stock engines in Texas. Can't kill 'em. It's not even synthetic.
 
#60 ·
LOL , a Forged piston when over heated can/will draw in on the skirts ( collapse ) causing it to be slightly smaller to the point you get some piston slap

This is from Probe and I can find you dozens more like it , I did a copy and paste so it wasnt taken out of context

A: Probe FPS Forged Pistons are designed for heavy duty and high performance use when the application requires a piston that is stronger than a Cast or Hypereutectic Cast Piston. They are suitable for heavy duty, high performance street and some race applications. Compression ratios are similar to factory applications and weights are generally lighter than the TRW equivalent. The FPS series is manufactured using the same ultra-modern machining techniques as the SRS and series pistons.

FPS - Technical Summary

Forged of VMS-75 High Silicon Aluminum for lasting performance.
Light weight forging design is typically about 70 grams lighter than TRW’s.
CNC Diamond machined skirts and ring grooves for increase power.
Tight piston to wall clearance design for better ring seal.
Reinforced piston skirts to eliminate piston skirt collapse.
Radial Anti Detonation Grooves reduce detonation by clipping pressure spikes.
Pressure Equalization Channel enhances ring seal, making more power and increasing fuel economy.
Increased valve relief depth for high performance camshafts.
Offset wrist pins for reduced noise and lasting operation.
Stock size rings grooves and press fit piston pins.

Probe SRS Forged Pistons are designed for performance and race applications where a strong, lightweight forged piston is an advantage. With well over 200 part numbers now in stock for popular Chevrolet, Ford, Chrysler, and Sport Compact applications, the SRS Series are a full-featured piston and are extremely popular for use in street and most racing combinations.
 
#62 · (Edited)
LOL I am not talking about the reinforced

" Reinforced piston skirts to eliminate piston skirt collapse. "

Not the reinforced skirt yes most Forged Piston Companies do that part but Probe specifically used the word collapse not break and Probe is a very well known Forged piston company

If I searched there is talk all over the net from major piston companies about piston skirts collapsing , just because you think its BS doesnt change its a fact that it happens

Tom
 
#64 ·
Ahhhh .... right

I have had more then likely 10,000+ sets of Forged pistons go through my shop , I know hands down that the skirts of a piston can collapse

Probe easily could of said breaking , cracking but they chose collapse and yes I am sure they chose that word specifically for there advertisement because it is a known problem and they addressed that specific problem and why its in the advertisement

Email and company that makes Forged pistons or call and ask them if its possible for a Forged piston to collapse with over heating it

Just because you dont know or think its BS doesnt mean it doesnt happen

Tom
 
#65 · (Edited)
To all concerned, I started this and shouldn't have, pistons CAN collapse................what I should have said was that they commonly don't collapse just a little to rattle a little bit like mentioned early on in this thread, rather, a collapse is a major fail pretty much rendering a part as junk. At least to me.

I apologize for any misleading I did there, it was wrong. I don't do well when trying to out bullsh-t people and that one is on me alone.
 
#67 ·
BTW - two definitions of 'collapse' led to the disagreement it appears.

Common definition of physical failure vs. a specific one of reduced diameter from a previous overheating of the piston.

Which definition was meant by the piston company quoted as evidence is questionable, as reinforcement to prevent physical collapse will NOT prevent the reduced diameter situation from overheating.
 
#68 ·
You are correct , In the world of pistons there is 3 things that can happen to a piston skirt , Break , Crack or collapse where the piston actually gets smaller in the skirt area when you mic it from excessive heat

Many things will break a piston skirt debris , to much timing , piston to wall clearance , to short or small a piston skirt for what your using them for etc most are from excessive skirt load

I have actually taken 4 pistons that had collapsed the skirts and bored the block to match them and ran them in my Focus for 6 years making north of 300hp to the wheels

Tom
 
#69 · (Edited)
They seize to remove the upper high points prevalent at the time it happens, it's called a seizure. 2 strokes can do that all day long, in fact you run them hard if a race engine and then pull pistons out and look for the seizure points to then dress them down and put it back together to run it again. Factory procedure for mechs racing back in the day and even now. I do it all the time.

If you truly have collapsed a piston you won't be running it again, it is no longer dimensionally stable as it has been yielded.............if it were possible think of the possibilities of someone 'rebuilding' pistons. Of course l like Tom I have done it, but I wouldn't call the pistons 'collapsed', they more accurately fit the definition of seized I gave above, the major piston shape is still 99.9% solid.
 
#70 · (Edited)
Seizure = " the action of capturing something using force." Webster ( can be seen with a visual inspection )

Galling = " Galling is a form of wear caused by adhesion between sliding surfaces." Webster ( can be seen with a visual inspection )

These words with definition are used commonly with pistons ( both meaning basically the same thing ) when the side wall of the skirts of the piston loose lubricant , excessive heat or excessive wear removing some of the outer layers of the piston and depositing them in most cases onto the Cyl wall

But here we are talking about

Collapse = " to fall or cave in " Webster

What happens is the skirts of the pistons fall in , get smaller , they dont brake , they dont seize they actually get smaller from when they were new/installed , the skirts still look to the eye perfect in every way , When gaulded or seized the skirts look almost like they were ground on , in most cases dark from the heat and in most cases deposits of aluminum on the Cyl walls

But when your mic the collapsed piston skirts there .003-.008 +/- smaller then they were installed or what the spec sheet was when the pistons were bought new which makes the pistons slap in the bore and causes a knock

The collapsed pistons are still very usable just not in the block that you did the bore for when they were first installed , bore a new block to match the piston size which we do with every engine we machine and the collapsed pistons work perfectly " the major piston shape is still 99.9% solid. " if it was 99.9% solid to start with

Only the piston skirt size changes , the ring area and everything else in most cases stays as good as it was new

" Piston collapse
A reduction in the diameter of the Piston skirt caused by heat and constant impact stresses. " http://www.motorera.com/dictionary/pi.htm#Piston_Collapse

A good read on how to measure a piston and how pistons can be reduced in size from collapsing
http://pautomotivemechanics.blogspot.mx/2011/06/piston-measurement-and-clearance.html


I hope this helps

Tom
 
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