Help! Shop wants $4,000 for used engine install, but can't confirm actual problem
 

Good morning, everyone.

I'm a desperate G35 owner trying to troubleshoot an engine issue. I appreciate any help you can offer.

Few details:
'03 G35 sedan with original VQ35DE engine. No mods.
128,000 miles

Problem:
A week ago, I redlined my car while passing a vehicle on the highway. As soon as I jumped past the vehicle, I let off of the throttle and starting hearing a knocking or tapping noise. I thought I may have busted a motor mount and that the cooling fan was hitting the shroud or something similar. I pulled over, shut off the car, and turned it over two more times before towing it to a shop. The car didn't show any codes, and the knocking sound is similar to a sound like a loose nut or rock bouncing around in the upper engine area. It isn't constant with rpms though it does speed up as rpms increase.

The shop disassembled the valve covers and the timing cover and timing parts, and they do not see anything wrong there. I was advised that instead of paying more labor for them to keep disassembling the engine to find the actual problem, it would be cheaper to install a used engine. However, the used engines they can source are $1800 and the labor is approximately 19 hours at nearly a $100/hr. The estimate is around $4,000 plus tax to put in a used engine. I'm not doing that. I'm renting a trailer and towing the car home tomorrow to try my luck at doing my first ever engine diagnosis and repair.

The mechanic thinks it is in the rods. He didn't do a compression test and he said he used a stethoscope to find the noise bounces around some but sounds like it is in the top of the engine. Since he couldn't find anything wrong up there, he thinks a rod bearing is vibrating the noise into the top of the engine.

I'm looking for advice regarding what to look for next and how to do that. I'll update as I have time to keep investigating.

Last details:
Changed oil and filter around 500-1000 miles ago to Castrol Edge 10w-30 (never used it before).
Dipstick oil looked clean and couldn't see any metal pieces.
Oil level is good.
When I purchased the car 15k miles ago, the previous owner missed an oil change interval and the dipstick did not read any oil. In retrospect, I should have walked away, but I hoped the engine was fine.

Any ideas where to look next to diagnose and hopefully repair?

Thanks.

I'm not an engine guy and it's probably not what you want to hear but if the engine runs I would keep going until it won't go anymore. If it costs 4k for a new engine, use that towards a different car instead unless you really want to keep your car. You could probably get a 2003 g35 with 150k on it for like 2500 so you get to keep the same car and not go through new engine trouble

I just sold my 04 g35 with over 200k on it for $1600. My burned some oil so if your engine is making noises I'm sure they won't pay much more than $1500....

.....On the other hand you might want to sell it before the engine locks up.....

Did they at least pull the lower oil pan down or look at the oil? I would take the lower oil pan off (it's screwed on and sealed with RTV). Then see if there is any metal debris in there from the bearings or something. If it's a constant knock with RPMs though sounds like you might have rod knock and your engine is probably/possibly toast. I don't think they needed to tear into all that though to diagnose that....sounds like they did that on purpose to sell you a used engine or get some "gravy" work.

There's an engine by me for 800.00 with 75k. He's definitely taking you for a ride. Shop around and get another opinion

You could always claim this as a comprehensive failure under my insurance policy. Check yours, might just claim it and move on.

Red lined with your mileage, what you're hearing is rod knock from spinning a bearing. Paying $4K for engine install is insane and way more hours than it should take! You should have asked them if you had "Stupid" written on your forehead? You have choices, shop around, find a Nissan shop/mechanic that will do the job reasonably or trade your G in quickly!
Gary

Yeah I wouldn't be surprised if a quote for a brand new engine from Nissan is only a couple hundred more than that quote.

Like a previous poster said drain the oil into a VERY CLEAN CONTAINER and drag a magnet through it (telescoping pick-up tool works perfect). If you find ANY level of metal shavings at all you can assume the motor is toast.

Now, about the noise supposedly "bouncing around", I've diagnosed quite a few rod knock, spun bearing sounds in the past and there's no way it's louder at the valve cover than at the oil pan, it echoes so loud at the pan it's literally 4-5x as loud at the bottom so.... I don't want to get your hopes up but it might NOT be rod knock.

If you're competent at taking bolts off I'd suggest ripping the motor apart, starting at the lower oil pan so look for amspun bearing, it's pretty obvious because it's not in a straight line with the rod cap or crank cap.

Since it was diagnosed that the noise was coming from the top and most importantly is INTERMITTENT I suspect you either shattered a valve shim cap or maybe spun a cam bearing, it's quite a few more bolts to get the top end torn down, ignition coil packs,spark plugs, intake plenum (upper and lower), and the valve covers. Next rotate the assy by hand and fully inspect each component.

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