Knocking on cold startup

[AK602]

OK Much to my surprise I have a problem that I am not happy with. I have a knock on cold start up that lasts almost 2 to 3 minutes. It is especially noticable in reverse and drive. Now just to let you all know I was a mechanic for 15 years and a service advisor for over 5. 3 of those years at toyota and almost a year at lexus. I am running mobile one since the first oil change and change my oil every 3500-4500 miles even with synthetic. I do alot of driving. I have 41,500 on her now.

This noise sounds to me (without getting under the truck) like a rod knock or piston slap, however not somthing I expected from the toyota v8 after 2 years and just over 41,000.

Has anyone experienced any of this. I did a search and came up empty. I swear I thought this was the greatest truck on earth. The only real warranty problem I ever had was the sun roof. I am gonna take it in next day or so.

ANY INPUT IS APPRECIATED.

Aron

 

[psychoklr]

I've got the same problem. It's hard to tell where it's coming from. Sounds like a knock though.

 

[AK602]

have you brought this to your dealers attention.......

 

[00328]

PLEASE, keep us updated on this!

 

[psychoklr]

No I forgot the last time I was in ... I will be going back tommorow since when I went to drive it today there was a puddle of AT fluid underneath Damn dealer must have left something loose on the last service.

GRRRR.........

 

[loner]

Oh crud... After dealing with piston slap in my 2.7L Tacoma, I thought my days of knocking engines were over. Hopefully your experience with Toyota will help you find a good resolution to this.

 

[SWUtah]

They have had this problem with the Tundra V8's, not a lot of them but some. It is piston slap and Toyota states that it won't effect the length of the engine life. It happens when it is very cool. Some state that it started when it was very cold and each year it keeps doing it at warmer and warmer temp's. Toyota will not correct and states it is not a problem. There has only been one Landcruiser that has reported this problem on any forum I've monitored. If it was me I would trade it before the engine warranty was up.

 

[pat161]

Well I have a 2.7 with the classic cold weather piston slap, which is harmelss and normal, but what this post describes is not the same. On mine, even when it is 0 or less out it will only knock for 10 seconds max, it has been exactly the same for 92k, the temperature at which it occurs has never changed. So if yours is knocking for 2 or 3 minutes or knocks in progressively warmer weather then you don't have the same issue, definitely get that puppy checked out before it's too late. On a side note everything I read says you should not put a load on the motor until the knock stops, so if you are driving like this then that is not good.

 

[SWUtah]

Pistons rock as they cross TDC where the thrust load from the rod angularity shifts from one side to the other. This makes noise. Harmless, but it is the source of piston slap in most all situations.

To prevent this, pistons are designed with long, tapered, flexible skirts so that they can be fitted very tight in the bores when the bore and piston is cold. The taper of the skirt and flexibility of the skirt then prevents scuffing when the piston is hot. Also, the piston pin in OEM production pistons is always offset to one side....it is NOT in the middle of the piston. By offsetting the pin in the piston, artificial thrust load is created to control the piston "rocking" as it crosses over TDC.

Unfortunately, all of the above control techniques, common in past model engines to the extreme, create excess piston mass, cause friction and cost power and fuel economy. With the desire to build in as much power and free-revving capability and to improve fuel economy as much as possible thru friction reduction these design features are pushed in the other direction on modern engines.

Piston pin offset has been reduced over the years to a bare minimum today to reduce the thrust load generated and reduce friction. Pistons have been lightened up considerably by shortening the skirts. This creates less rotating/reciprocating mass which is good for power, free revving capability and fuel economy. Light weight pistons are great but the skirts, by necessity, are short making it hard to make them both strong and flexible and the shorter ckirts make them more prone to rocking.

Unfortunately, when the performance or fuel economy oriented pistons are run cold they are very prone to "slap" until they warm up to operating temperature.

The piston designers and development engineers are always treading the fine line between piston slap cold and friction and power/fuel economy loss when the engine is warm.

It is possible that you are hearing piston noise from an engine that is on the "high limit" for piston clearance so that it makes some noise cold. The good news is that the condition is harmless and that engine is probably a little more powerful (due to less friction) than a "quiet" counterpart. The bad news is that...it makes noise cold.

 

[Fro-Runner]

Pistons rock as they cross TDC where the thrust load from the rod angularity shifts from one side to the other. This makes noise. Harmless, but it is the source of piston slap in most all situations.

To prevent this, pistons are designed with long, tapered, flexible skirts so that they can be fitted very tight in the bores when the bore and piston is cold. The taper of the skirt and flexibility of the skirt then prevents scuffing when the piston is hot. Also, the piston pin in OEM production pistons is always offset to one side....it is NOT in the middle of the piston. By offsetting the pin in the piston, artificial thrust load is created to control the piston "rocking" as it crosses over TDC.

Unfortunately, all of the above control techniques, common in past model engines to the extreme, create excess piston mass, cause friction and cost power and fuel economy. With the desire to build in as much power and free-revving capability and to improve fuel economy as much as possible thru friction reduction these design features are pushed in the other direction on modern engines.

Piston pin offset has been reduced over the years to a bare minimum today to reduce the thrust load generated and reduce friction. Pistons have been lightened up considerably by shortening the skirts. This creates less rotating/reciprocating mass which is good for power, free revving capability and fuel economy. Light weight pistons are great but the skirts, by necessity, are short making it hard to make them both strong and flexible and the shorter ckirts make them more prone to rocking.

Unfortunately, when the performance or fuel economy oriented pistons are run cold they are very prone to "slap" until they warm up to operating temperature.

The piston designers and development engineers are always treading the fine line between piston slap cold and friction and power/fuel economy loss when the engine is warm.

It is possible that you are hearing piston noise from an engine that is on the "high limit" for piston clearance so that it makes some noise cold. The good news is that the condition is harmless and that engine is probably a little more powerful (due to less friction) than a "quiet" counterpart. The bad news is that...it makes noise cold.

"Whew".........I believe this is going to be over many of our heads in here! Thanks for the pistion slap information anyways.