Warm up with piston slap?

[Kira]

Given the breadth of automotive topics here, I'm surprised to read of so much piston slap.
M
It appears many drivers cope with it regularly and over a long time.
Do owners trade or dump a vehicle with piston slap more readily?
The anecdotes seem heavily GM?
Does the industry track items like piston slap, or excessive piston slap?

 

[FCD]

My 75 Capri has had a slight knock on cold start for a loong time that lasts no more than a second , but it doesn't always do it, in fact lately I haven't heard it for a while, then sometimes i'll hear it maybe in 1 out of 4 cold starts, just randomly it'll do it.

I guess it's piston slap, some people have suggested to me it may be a wrist pin noise, but it's done it for years and has not changed at all so i am not worried , runs great, i pulled the heads 3 years ago off and all the bores look perfect so i don't know, I don't think it's a rod knock either.

 

[FCD]

Given the breadth of automotive topics here, I'm surprised to read of so much piston slap.
M
It appears many drivers cope with it regularly and over a long time.
Do owners trade or dump a vehicle with piston slap more readily?
The anecdotes seem heavily GM?
Does the industry track items like piston slap, or excessive piston slap?

All i know is people I've talked to people who say forged pistons tend to cause piston slap more than cast?

 

[ls1mike]

It is the short skirt in LS engines. The cylinder rocks around a bit until it warms up.
All of mine have done it. So does my LT engine in the 2024.
Only does it cold. It is a non-issue. I think most LS engines are hypereutectic pistons except for the LS9.
I do believe the L8T in the truck has a hypereutectic piston as well.
100s and thousands of miles on tons of LS stuff with no issue.
It is much louder in the aluminum block stuff. If you don't hear in your LS based engine you just need to listen a little
harder on a cold morning.

 

[dja4260]

My 2013 Hyundai Elantra GT had horrible piston slap when cold, upon start up. This was prior to the countless failures and recalls by Hyundai. I brought it to a dealer and they "didn't hear it." With that said, I sold it 5+ years ago @ 88k trouble free miles.

 

[repairman54]

Had 2 '03 3.1 Malibu's in the family, one mine the other my sisters. Both bought used at 75k from a Co. fleet (wife's job). Mine was quiet, my sisters sounded like a diesel on a cold start. Sister drove it to 150k and traded it in running fine. I got a great deal on it when negotiating with the fleet manager when he heard it cold start.

 

[bubbanik]

I can actually tell you what GM recommended in its engine classes as this was always brought up. The engineers always said it was best to let the engine warm up to 120 degrees before driving off easy. Many years later in my 2013 Subaru Forester with a cold engine light I hooked up my scanner out of curiosity. Sure enough the light turns off at 120 degrees. I had remembered the recommendation from the mid nineties.

My new 2025 Mazda CX-5 also has a cold engine light. I'd never seen one before and had to research to see what it was I was looking at. I haven't hooked up a scanner but the digital temp gauge on the vehicle is "blue" from start-up until 120 on the gauge which is when the light turns off. I don't worry too much about it, this car takes awhile to warm up, but my wife REFUSES to even consider moving the car until that light turns off. But this is also a woman who turns off the radio, AC/heater, and/or anything that is in the "on position" before she turns the car off. Can be a little annoying but I guess it just shows she cares about the car and takes care of it.

 

[BrendanC]

02 6.0 LQ4 i let it warm up atleast until the needle moves off of the cold stop. most times i start it and continue getting ready. 9k engine hours and 240k miles later zero piston slap or valve train noise

 

[notharry]

its the piston design mostly. light weight Skirtless pistons. our 2008 ej2.5 slaps the same now at 192000 miles as it did at 20,000 perhaps since new. My wifes 2.5 fb in her 2017 subaru engine is almost more noisy than the 2008. Subaru is like YEA... its fine. Boxer engines have more anyway because of the configuration but as hp goes up on small engines more heat expansion needs more clearance. Yes its annoying. going up a weight helps. Do what you want warm or not. I.. not just drive sensebly

 

[bubbanik]

I had an old chevy van that would slap when cold. I read around on what really causes it, and can't believe it was meant to do that from the factory. I like to try and cure a problem on the cheap side, so here's my hack. I bought several different brands of oil filters and tested them until I found one where I could barely hear a slap. Then used that one until I got rid of that vehicle. It seems alot or most filters go into bypass mode especially when oil is cold and thick. Which I understand, but some brands are still are too restrictive. This "cure" obviously will only work with spin on filters. I never had a vehicle have the slap issue with a cartridge type filter.,,

I did the same thing with the 2020 Kia Soul that I recently dumped due to a bad motor.
The piston slap on that thing made it sound like a farm diesel. I started using Napa filters instead of OEM. My wife was astounded at how much quieter it was at start up. Told her it wasn't a fix, that nothing I did was going to save this engine in the long run, but it was definitely quieter in the morning.
It blew up anyway. Ha!

 

[OVERKILL]

its the piston design mostly. light weight Skirtless pistons. our 2008 ej2.5 slaps the same now at 192000 miles as it did at 20,000 perhaps since new. My wifes 2.5 fb in her 2017 subaru engine is almost more noisy than the 2008. Subaru is like YEA... its fine. Boxer engines have more anyway because of the configuration but as hp goes up on small engines more heat expansion needs more clearance. Yes its annoying. going up a weight helps. Do what you want warm or not. I.. not just drive sensebly

Yup, it's the combo of short pistons with short skirts and the transition from hand-fit slugs to bulk-fit in the assembly process, to make it quicker. Many engines ended up with slugs that were a little loose but still within spec, which, in a hand-fit application, that hole would have got a larger piston. This was later addressed via coated skirts (what @Glenda W. mentioned) and updated pistons with slight changes in the skirt design.

The move to these super short pistons was of course done to reduce friction. Reduce the amount of metal sweeping the bore, which improved efficiency. This was combined with pushing the ring pack up higher, which we discussed in a previous thread.

Stock LS1 pistons:

Piston/rod from an 80's 350: