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Knocking Sound When It Starts


lexxus
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I posted about this before. I discovered a receipt from the former owner of my girlfriend's car, and he complained to the dealer about "ticking valves on startup". They changed the oil and put the right oil filter on the car. Couple of years back, apparently. Well, now I've just noticed this weird knocking sound on startup. It's not valves. I think I know what valves sound like. Noy ticking exactly. More like a knock. It goes away immediately, but it worries me. If it was a rod knocking, or something serious, I guess it would be much louder, right?

It only happens when you first start the car, and it doesn't make the sound after that.

What could it be, and is it something to worry about?

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I think the last time this subject was brought up was with a valve issue. Somebody talked about cleaning the valve cover.

Can you tell me what it sounds like, timing off it and so on?

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It only happen when you first start the car, then it goes away. But it doesn't sound like valve clatter or lifters. I was a street racer as a teen, so I sort of know sounds. It's not a water pump bearing, or the ac bearing, or the fan hitting something. It's a knock, a deeper sound. I've noticed it quite a few times now. And the car runs like a rocket.

Back in the days, we used to say that a motor would get really fast right before it was going to blow up. But these were Chevy small blocks revving at 8 grand and taking punishment.

I'll bet that this is the sound that the former owner complained about, so it's been doing it for a couple of years.

The oil is clean, and the car seems to have been well taken care of.

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My 92 sc400 also makes that knocking noise upon start up. It's been doing that for the past 10 months that I've owned it. I also read somewhere on a different forum that the noise was probably from the waterpump. After they changed their t-belt/h20 pump, the noise went away. I'm not sure if it's true, but I'm gonna get a t-belt/pump/seals/sparkplugs & wire/cap/rotor changed this thursday or friday so I'll find out by then. I fit doesn't go away, then I don't know what the problem may be.

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i think i had the same thing. you can hear one knock on start up right? i changed the motor, and trans mout and it wet away. i was guessing that when the motor torqued on initial fire up on bad mounts it was hitting the chassis or something and making that noise. mine didnt happen every time but fairly constantly. so i changed the mouts and i havent heard it since. so if your mounts havent recently been changed give it a try.

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Know this issue well:

If considerable miles on engine, high probability main bearings are worn or gap specs are too wide as they will tend to knock for a few seconds until oil pressure gets oil to the bearings. Also, engines can be assembled with wider than standard bearing gap specifications that will subtley knock the same. Years ago for drag racing/performance purposes, we use to spec wider to lessen friction drag on engine -- but not an acceptable concept for daily drivers nor a practical financial matter in today's environment.

If due to high mileage engine or natural wear on the main bearings, the engine can still last a very long time with moderate driving. If driven a lot or very hard, main bearings will eventually have to be replaced -- by that time usually makes sense for complete engine rebuild or replacement.

Lower end multi-viscosity 5W - xxW can help by enabling the flow of start up oil quicker. One qualifier is to try higher weight viscosity like straight 40W for a couple of days to see if takes a couple of seconds longer for knock to subside on start up -- if so, then almost 90 percent probability it is the main bearings. Change the oil though to mult-viscosity as that "knock" is hard on the remaining bearing/crank surfaces.

A professional mechanic (with some high mileage on him as well) will be able to tell if rod or main bearings. In either case of rod or mains, will progressively worsen over time and risk damage to engine if ignored.

Good luck and looking forward to determined problem answer.

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Obviously, I'm really upset. What will it cost to fix this? The guy would not come down in price, and we paid him KBB for the car. And he swore it had no issues. Then, I see in the receipts that he took the car in for this very problem. He had an extended warranty. I'll bet that the dealer knew all too well what this sound meant, and they didn't want to fix it. They just changed the oil and filter.

Oh man.

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Lexxus,

Knock issue may not be as bad as seems. Have to narrow down the possibilities and then evaluate some reasonable options. Need trusted mechanic to evaluate as could be something less serious. Regarding your last post...

1) If original complaint by orig owner to dealer/shop was valve ticking sound, as you mentioned, distinctly different sound and issue. Some engines varnish up and valves/lifters stick intermittenly -- that is cleared up with detergent mix like "Mystery oil" briefly run in the engine disolving the varnish.

2) Mainbearing knock usually only after car has been sitting overnight or engine cold, mechanic may not hear it if he worked on the car within hours it was brought in. During initial stages of mainbearing knock, symptons are not audible after first start up for the day. Whereas, rod knocks are more distinct as a rule and tend to worsen quickly.

3) Also, initial stage may only be noticible in cold weather since oil is thickened after sitting overnight or extremely cold weather during the day.

4) Depending upon prior maintenance oil change quality/schedule, mileage wear, the circumstances knock appears, cold climate environment, driving habits and to what extent using different viscosity oil alleviates the problem, etc. the engine can last for years.

5) Many high mileage cars on the road have very subtle start up knock, but average person does not hear or notice it. They are the lucky ones as they do not know enough to worry about it.

Questions:

1) What is actual mileage and year of the car?

2) How many average miles in a year will car be driven? What will be net value of car in one, two or three years? If main bearings are the problem, is the car worth the engine or best to trade in on newer car in next three years while it is still very functional.

3) Do you have a mechanic you personally have confidence in to level with you?

4) What viscosity oil are you using now?

5) If you change the oil filter to another brand or quality, does it make a difference (some oil filters give better free flow than others), etc.

Good luck and keep posted of results as you sort it out.

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The original owner complained about the sound on two different occasions. Two different dealers too. First complaint "when started cold has loud lifter noise." The dealer said that it had an aftermarket oil filter with no regulator, so they installed a Lexus filter. The second time he took it to another dealer, this time complaining about a "rattle". They said that the vehicle operated normally. The owner had no idea what the sound was. And yeah, like you said, the mechanics worked on the car after it had been driven on both days. The knock is only when you start it up cold after it's been sitting overnight.

It's a 93 sc300, with 84,000 miles. Pretty clean, but not pristine. Good condition. I have no idea what kind of oil is in there now, but I'm going to try what was suggested above.

I'm a car person, and I think I know lifter/valve clatter. And I've heard rods knocking before. They're distinctly different sounds.

I'd walk my girlfriend to the car, and I'd hear it, but I've been in denial about it. Disbelief. Because the guy really seemed alright.

But hell, a mechanic wouldn't have heard it either, since it only happens the first startup of the day.

My girlfriend drives a lot, both to school and to work.

I really appreciate the advise here and the concern. Many thanks.

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Mine does it too, it's a 300 with 45k miles. I've been a mech. my whole life & know it's bottom end,(mains/rods). It's mostly drain back after 8 hr. of sitting, worse in winter, worse with Mobil 1 than reg. oil. I use oem filters supposibly with a built in check valve, I sure don't like to hear it but don't think replacing bearings is nescessary or would even correct it.

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Taped the sound all week, took it to my mechanic. He said from the tape it sounds like a bearing. I'll have to leave it overnight for a cold/morning start.

I've been informed that I should take the guy to small claims, since he swore that there were no problems, while there were TWO service order receipts from Lexus for this very issue. Fraud/misrepresentation?

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Tracking this issue of "knocking" or main bearing "rattle" on start up of cold engine. Intriguing because of some respondents indicating their engines doing the same thing with relative low mileage.

Having purchased a beautiful SC300 (I know the car and the owner is a friend) in pristine condition, I am new to Lexus and their engines -- so I am learning as well.

But with prior experience of years with performance cars and engines, it is not normal that main bearings should be rattling upon cold start -- unless the engines have been oil change neglected or have much more miles than indicated.

On the plus side, if turns out that main bearing gap specs are a little wider for whatever reason, then effective oil/oil filter measures to minimize rattle may enable the engine to last for many years -- just depends on extent of main bearing wear.

Would like to hear other suggestions, opinions or facts from those with Lexus experience. Looking forward to Lexxus diagnosis progress as well.

Regarding Lexxus "Small Claims Court" issue: Problem you will have is that the prior owner did go to the Lexus shop with questions and the "Lexus experts" declared car is "operating normally." Therefore, as convoluted as it is, the owner told you best he knew based upon the experts he relied upon -- which makes for another intriguing situation around whole issue.

And if there are other cars (johnny3) that have a main bearing rattle at 45K miles, then one could claim it is "operating normally."

Could be entertaining automotive soap opera material if it did not cost so much money and make one worry about it.

Good luck...Lexcalibur300

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Well...actually he out and out lied. I asked him many different ways, Have you had ANY problems with this car?" "Is there anything that needs to be done to this car?" Over and over. He no'ed me every time. Then my girlfriend tells me about the "weird sound", and I find the two work orders in the glovebox. My mechanic says it's the reason he sold the car. You see, it ONLY happens with the engine COLD, first thing in the morning. So, the best mechanic isn't going to get the full impact of the loud rattle if the car has been started previously during the day. Yeah, used cars are buyer beware and all that, but this dude warmed the car up before I got there, so the knock wasn't evident.

You know. if he'd given me a good deal, I'd back off. But we paid him Blue Book, and he would NOT come down, so I thought it must be a really solid car. Once more, my trust in humanity backfires.

Yeah, I really would not expect problems with the number one car in the world until much higher mileage, and it is deeply disappointing.

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Ok, got it -- the guy is either ignorant or a crook! In either case, once you have determined situation with facts you can go back and explain asking for either total refund or adjustment. If honorable person he may listen and try and work it out. Or, if a jerk throw you out immediately. Or if an outright crook, may just try and beat tar out of you to scare you off -- hey sounds like 33% chance to work it out!

Do you have any way with service records or otherwise to determine if mileage is correct on the car. That is another discussion issue if does not reconcile and that gives you some leverage with prior owner.

Back to the "rattle" (sounds better than knock) -- has your mechanic confirmed it is main bearing rattle?

What are the mechanic's suggestions? Did he suggest it might be "quasi normal" for this engine with some miles on it?

With only 84K on engine (if that is true number), what would the mechanic charge to drop the crank and replace with replacement bearings (actually curved bushing)? I do not know enough about these cars or engines to know if possible with engine left partway in car or if whole engine needs to be removed.

If it is mainbearing rattle, what kind of oil filter has been in the car?

If "El Cheapo", next step is the correct oil filter with a valve retaining oil in the filter for immediate supply to the engine on cold start. I did see your inquiries about the appropriate part number on the forum. Note, seems like Lexus dealer would have put in the appropriate filters in the past, but could be prior owner was using a quickie lube for his oil and filter changes and they provided another type filter.

Are you going to try 5W - 30W oil to see if helps get oil to bearings quicker? Of course, without knowing current type of oil in the car difficult to know if will make a difference or not.

Johnny3 response as a mechanic is interesting view that he did not think bearing replacement was necessary nor would fix the problem. Hopefully, he'll explain further. I do agree that main bearing rattle may not be as bad situation as it seems right now until have tried some things.

Keep us posted -- without knowing current oil and filter, my hope is engine responds to thinner oil and better designed filter.

Good Luck....Lexcalibur300

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Ok, got it -- the guy is either ignorant or a crook! In either case, once you have determined situation with facts you can go back and explain asking for either total refund or adjustment. If honorable person he may listen and try and work it out. Or, if a jerk throw you out immediately. Or if an outright crook, may just try and beat tar out of you to scare you off -- hey sounds like 33% chance to work it out!

Do you have any way with service records or otherwise to determine if mileage is correct on the car. That is another discussion issue if does not reconcile and that gives you some leverage with prior owner.

Back to the "rattle" (sounds better than knock) -- has your mechanic confirmed it is main bearing rattle?

What are the mechanic's suggestions? Did he suggest it might be "quasi normal" for this engine with some miles on it?

With only 84K on engine (if that is true number), what would the mechanic charge to drop the crank and replace with replacement bearings (actually curved bushing)? I do not know enough about these cars or engines to know if possible with engine left partway in car or if whole engine needs to be removed.

If it is mainbearing rattle, what kind of oil filter has been in the car?

If "El Cheapo", next step is the correct oil filter with a valve retaining oil in the filter for immediate supply to the engine on cold start. I did see your inquiries about the appropriate part number on the forum. Note, seems like Lexus dealer would have put in the appropriate filters in the past, but could be prior owner was using a quickie lube for his oil and filter changes and they provided another type filter.

Are you going to try 5W - 30W oil to see if helps get oil to bearings quicker? Of course, without knowing current type of oil in the car difficult to know if will make a difference or not.

Johnny3 response as a mechanic is interesting view that he did not think bearing replacement was necessary nor would fix the problem. Hopefully, he'll explain further. I do agree that main bearing rattle may not be as bad situation as it seems right now until have tried some things.

Keep us posted -- without knowing current oil and filter, my hope is engine responds to thinner oil and better designed filter.

Good Luck....Lexcalibur300

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  • 3 months later...

I've had the same problem with our '95 SC 300 since we purchased it Margate Lexus with 64k on it. See: http://us.lexusownersclub.com/forums/index...wtopic=8030&hl= The engine had just had the Bilstein Flush when I purchased it and for a short time, I thought the flush had damaged the engine. The engine now has 106k on it. I've since tried another engine flush thinking it would help if the noise was caused by sticking valves. The flush didn't help. I've had the valve lash checked and even purchased one of the valve lifters and cut it in half to make sure it wasn't a hydraulic valve lifter with seals subject to leaking (it was solid). :wacko:

The most recent effort was to have the timing checked and reset. :unsure: Turns out the timing was out of spec, advanced about 5 degrees. The reason I thought of timing was if the timing was too advanced on a cold start startup, the ignition would go off way before the piston was reaching top dead center thus causing the knocking sound. As I understand it, on a cold start, the ignition is told to advance by the control module, and the flow from the injectors is increased (unless there is a cold start injector present). This creates the optimum cold start environment. As soon as the the engine starts, the control module reads the various sensors then takes command of and re-adjusts the timing, then slowly leans out the flow of the injectors as the engine warms. I asked the tech to check how much the computer was advancing the ignition but he didn't have a way to check it. I think it may still be over advancing the ignition on a cold start startup. With the timing reset, the cold start startup has much less knock, but there is still some knock and a very slight miss until the engine warms.

I'm almost to the point where I'm ready to put another engine in or have mine rebuilt. I've even been watching Ebay for a replacement engine.

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