Hi! I have a 2009 Lexus IS250 (V6 2.5 liter RWD) with 197000 miles on it. There's a story with this- bear with me. I had the alternator replaced on this car. I tried to replace it myself first and was so angry by the time I was done messing with it that I brought it to a mechanic. I work an hour away from home. I drive it home and it runs perfectly. I get in it the next day to go somewhere (I don't even remember where) and it cranks just fine and drives for about half a block and the motor just dies. No strange noises, wasn't overheating, none of that. I try to start it back up and it tries to start but won't fully start, it just bubbles up and dies. Upon further inspection on my part, it is running no codes, and has nothing stored. My first reaction is to think fuel pump or starter. I wasn't sure and limited on funds, so I have it towed a mile away to a mechanic, who states there is low compression in 3 cylinders. This is a new mechanic I haven't used before (mainly because my last mechanic was not so great.) He gives me a quote for a motor replacement to the tune of some $5000. Upon picking it up, he thinks maybe the timing chain failed. My two questions start here: if it is the timing chain failing, did it ruin that motor? Based off the symptoms described above, do you agree? The oil wasn't low or discolored (it did need an oil change) the coolant wasn't low or discolored.
Your 2.5L Lexus engine is a Non-Interference engine (1) so a broken timing chain wouldn't destroy the engine.
That said, a timing chain breaking on a Lexus with under 200,000 miles would be extremely unlikely. (not just getting hit by lightning unlikely, like getting hit by a meteor unlikely).
Let's look at how your timing chains are setup.
You didn't say which 3 cylinders had low compression.
It doesn't matter. The camshafts on both cylinder banks are setup the same way.
The large Timing chain turns the intake cams and the secondary (No. 2) timing chains are connected by sprockets on the intake cams to turn the exhaust cams.
So if your mechanic thinks a No 2 timing chain is broken he could simply pull off a valve cover and look.
But I don't think this is the problem.
I think the problem is related to the symptom that made you change your alternator
(1) http://yourcarangel.com/2014/07/interference-engines-complete-list/
https://naijadriva.wordpress.com/2015/07/23/interference-and-non-interference-engines/
If the timing chain actually failed, it wouldn't run at all. I would definitely find another mechanic.
I think he said 2, 3, and 5 but I'm not completely sure. I'm picking the car up tomorrow and I'll ask. The cars battery light was flashing and the battery was dying daily, hooked it up to a scan tool and tested the alternator and it tested bad. I'll post again tomorrow with the for sure cylinders he said had low compression.