Car is a 1998 GS400 w 71k miles. Occasionally (once a month or so) if I leave the car parked and unstarted for a while (few days to a week) in cold weather when I start it up it makes a pretty loud rapping/knocking sound for the first few minutes. It goes away, but it doesn't sound like a lifter, it sounds like a rod knock, or worse. Is this common? will an engine flush help? Does oil viscosity matter? Any brand suggestions on flushes? I was going to buy the BG brand...

Thanks

Bryan

 

if it goes away it isn't a rod knock. Very unlikely it is an internal engine problem at that mileage with a Lexus.

Sounds like an accessory bearing is going bad. Possibly one of the following: tensioner pully, water pump bearing, AC compressor, ps pump, alternator.

Before you do anything, verify where the sound is. Take a long steel bar like an extension bar or very long screwdriver and hold it to various accessories and the engine itself in different places to try to find the source when you first start it. Hold the end of the bar in your hand and put your ear up to the end. Needless to say, be extremely careful for moving parts and hold the bar loosely incase something catches it.

Is you AC on or off? next time you start it make sure the AC is off before hand (manually turn it off) and see if that is it. If so compressor might be going bad, not uncommon after 8 years.

 

if you have thicker oil it will take longer for it to make it's way around the motor on cold start up, especially in cold weather.

 

the same thing happened to me a couple of times to my 98 gs400 and i posted it on here, i got a few different type of answers.... one was that the oil turns extra thick in the cold weather and has trouble moving up for a few minutes... they claimed it was normal...another was "valve tapping" its a pretty common problem.... not sure what fixes it.... happens to me still once in a while... if u find out the fix for it, let me know.

 

Try a good full service fuel system cleaner such as Valvoline etc. don't just get injector cleaner, get the complete system cleaner, in addition to seeing it happen I have been told by Lexus service techs that this is fairly common for cars that sit for periods of time, you may need to repeat this 2-3 times but this is the cheapest and best place to start.

 

I use BG44k fuel cleaners every 10-12K, I beleive it is either that the oil is too thick -- as both times this has happened it has happened on this oil change -- or that I have some gunk that freezes easier than the oil and sticks up a lifter or some other part...

 

what weight oil do you use?

 

Gravity still works. The longer your car sits more oil will drain down to the oil pan and things will rattle on first start up. I don't know if Lexus has hydraulic or solid lifters, I would guess hydraulic. Over time they too will bleed down from the pressure of the valve springs creating a dreadful rattling sound. Cold weather just makes this condition last longer and sound worse until the oil can reach temperature and flow easily. Don't rev the engine during this time, let it build pressure. A good winter blend (5W20) will help on start up during the cold season. Here in Alaska for last 20 winter seasons, the cars I don't drive often during the winter still get started every few days and are allowed to reach operating temps before shutting them down. Works for me with very little lack of oil rattles.

 

I don't know what viscosity oil the folks at VIOC used, I ask for the Durablend and never specifiy what viscosity because this particular VIOC is real good and always makes me feel like they are competent. What should I be using this time of year in Northern VA? Night time temps in the upper 20's and warmer for the most part? Highs in the upper 40's and warmer?

 

You should be running a 5w-30. If it is noisy for several minutes as you originally stated, I don't think it is oil related as even a 10w-30 would be circulating well at your startup temps within 15-30 seconds. If you were in Canada and seeing -30, then you might have something.

I have started my 430 at 25 degrees (coldest so far here) and have no noise at all. I stand by my other post--check your accessories for a bad bearing.

 

Get a proffessional emmisons cleaning. You can get it done at any quick lube place. My guy uses this product, and it is very effective. http://www.run-rite.com/industry/products01.htm