Originally Posted by mcfly0913

I just bought my '06 V6 Sport with 149,000 miles on it. No problems as of yet.

Originally Posted by blackmax

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- And 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.

Originally Posted by Drcoffee

Just bought this 07 sport 4runner and found a radiator leak the next day. So I changed the pump, radiator and spark plugs. Holy cow! It had the original spark plugs still at 222,000 miles. All gapped around 0.078”. #6 caught my eye with some residue on the ground strap. I have no symptoms, no cel, no white smoke. I hope it lasts for a while.

Originally Posted by Deckard2049

Great info on this forum!
I have a 2005 with 158K on it. I am trying to figure out if I have this dreaded head gasket issue. I have had my truck in at my mechanic three times since May.

I've had the CEL with the VSC lights on for each visit. Currently the lights are not on. The truck has had the following done:
-New fuel vapor pressure control
-New plugs
-New ignition coil
-New rotors / pads & calipers

Dumped a good amount of money into this truck this summer and am really hesitate to put any more into it.

Currently I am experiencing:
-Rough start
-Intermittent AC -- AC will work for a bit, but then cut out. Seems to happen more when it is hotter. Also seems to happen more when the air circulator button is off
-Losing coolant - I've filled the reserve three times since July and the radiator once. I have found no visible coolant anywhere near the truck after it has sat.

During the second trip mechanic felt that due to the locked up calipers the truck was running super hot and losing coolant. He checked levels and reported all good. Week later - reserve tank empty!

It's had the following codes:
P0441
P0117

On the advice of a mechanic friend I have it going to a local dealership for a diagnosis. $65 for a coolant pressure test. Is there something else I should ask for?

I have some froth discharge on the oil cap, but nothing covering the cap. Occasionally I will smell exhaust - but I have not seen any white smoke.

Any and all tips are very much appreciated.

Originally Posted by 4myacts

Sorry to revive this old thread, but I am a new member and it wont let me make a new post. I just purchased a 2006 4runner with the 4.0 and 138k. Is this issue inevitable or is it something I really shouldnt worry much about? Reading all the head gasket posts on the 4.0 make me want to sell the truck already.

Originally Posted by twa318

Look at the drivers side door jamb, there is a tag that has the build date on it.

If your build date is 11/05 or later you have the newer style gasket and have nothing to worry about unless the truck is showing symptoms.

I attached a picture of the old vs new style gasket, you can see its a different design.

Personally from reading all these threads over the years I get the impression early HG failure is mostly due to owners not using Toyota approved SLLC or disregarding the service interval for coolant flushes.

Originally Posted by 4myacts

Thanks for the info. It says 1/06, so I guess it’s right past the cutoff. Besides a minor oil leak (thinking timing cover,) it’s a great running truck. No signs of bubbles from the radiator or brown snot under the oil cap. I’m praying to get another 100k out of it at least. Do you know a way to check if the coolant is good? It’s red and clear.