sorry for kinda long.....
So, P0306.....it seems to be something of a "known issue" for the 4.0 liter engine. with higher miles. However, it's also true that reading a forum can make things look more prevalent than they really are. If 8 people all come on and say "Yea, me too"...it sounds epidemic. But maybe it's just 8 out of 300,000. Or maybe it really is a problem and needs to be considered.
Anyway,it seems that quite a few people have complained that they got the dreaded P0306 code (misfire in #6). Many then took it to the dealership who promptly nailed them for a "tune up" including plugs and a coil....only to eventually get to the real problem- "your head gasket failed at #6; and it's leaking coolant into the cylinder. You're F'd." It seems as if ALL of these people were at 120,000 - 160,000, with the majority seeming to be right at 150,000 miles.
Symptoms beside the code would be rough (as if missing a cylinder) at startup, especially after sitting for while.
I'm wondering if most or perhaps ALL V6s over 100k miles have this leak, but it's so small that it simply isn't noticed (yet); plus, it seals back up very quickly after startup, due to the intense combustion temps? After reading all the post on this subject, I'm convinced that mine has had this small leak for 100k miles now. It must just be soooooo small, that it hasn't become (and perhaps never will) a major issue. Why do I think I have a small leak, and have for long time? Here's what I've experienced-
1- maybe 10 times since I bought my truck (10 years ago) it shuddered for 5 seconds after startup....but later smooth out.
2- a couple times in summer, while climbing a hill, I could see white smoke in my rear-view mirror. Why it's only happened 3 times (that I know of)....I can't say. But I know it did happen.
3- A
nd this is the big one for me: I pulled all the plugs. They ALL look exactly the same......except #6! It had significantly more deposits on it (not black).
Now, like I said, I'm wondering if perhaps
most 4.0 engines have some leakage at #6 (seems it's an admitted design flaw, and Toyota has changed the HG design, as I understand it), but since the leak is so small, the owner is just unaware. So the real question is- how many drivers have over 175,000 miles on their 4.0 and
have not seen the CEL come on, and find out it's P0306?
Sorry for the length....but this could be a serious issue for people wanting to get high-miles out of their 4Runner, like me. I wonder if:
1- everyone with over 100k miles on their truck pulled the #6 plug plus any other plug....if they'd see an obvious difference with lots more deposits on #6? or,
2- not that many would, and the real truth is that though HGs will fail on our engine, just like
any engine, it's just that when it does n ours, it happens at #6.
Again, sorry for the length.
