Hi all,

As the title states, I have the p0300 code on my 2008, RX 400H, with 15xk miles. Made in Japan.

I don't know much about cars but have my own scanner and found 4 misfires and the p0300. My mechanic changed all 6 spark plugs and coils and the 4 misfires went away and are fixed.

However, the p0300 and Shaking when starting the car has been a huge issue.
My mechanic took apart the cylinder head(?) and did some diagnosis..and found that the head gasket is leaking and is essentially failing.
he also mentioned some maintenance issues like that I need a new timing belt and water pump.

But the main concern is the p0300 code and head gasket. Does this sound accurate ? what are your thoughts on his diagnosis?

The cost for all 3 replacement is 3,400 usd.

Thanks,
David

Hi BALexus, welcome to Club Lexus!

Really hard to say about that diagnosis.

Some things that come to mind:
1) We have 2 head gaskets on our cars- front bank and rear firewall bank, which one?
2) The timing belt will need to come off to do either head gasket so no extra labor should be charged for this- recommend replace the pulleys & hydraulic tensioner while you're in there, oem only.
3) It's a good time to replace the water pump while you're in there- coolant needs to be drained and T-belt removed anyway so this should add no more than maybe 0.5 hrs, if any.
4) What is included in the head gasket job? new oem head gasket I hope and new head bolts, all oem.
5) Does the price include machining the head if needed and if so what is included? new valves, etc, what?
6) Plz provide a beakdown of the prices.
7) Most important- how was this diagnosed? If he pulled off the cylinder head to look as implied someone may be pulling your leg- they would've had to put new head gasket to get it back together already.

If all he is doing is pulling it down and slapping on a head gasket that sounds like a heck of a lot of $$$.

Hi Margate,

1. Front.
2. "2) The timing belt will need to come off to do either head gasket so no extra labor should be charged for this- recommend replace the pulleys & hydraulic tensioner while you're in there, oem only."
THanks for the help. I'll ask. They would not go below $3400. Btw, I'm getting 3 coils and spark plugs replaced for free ($450) charge if I go through with the 3 aforementioned repairs. That was part of the deal. Forgot to mention. So repair is ~3000. I think that's one major reason why they won't go lower. How much do you think it cost to replace the head gasket, timing belt and water pump???
Bay Area mechanic shops.

3. "3) It's a good time to replace the water pump while you're in there- coolant needs to be drained and T-belt removed anyway so this should add no more than maybe 0.5 hrs, if any."
I see, thanks again for the info and help.

4. "4) What is included in the head gasket job? new oem head gasket I hope and new head bolts, all oem."
I Hope so too! They used OEM timing belt for my dad's RX. Toyotas would be cheaper.

I was told by another mechanic that they should install new cover for the head gaskets. I honestly wish mechanics took photos or explained more about what's going on with client's cars and how they plan on fixing it. Not even in writing or verbally, do I ever get a clue of what they're going to do. Very vague and general. 3 things next to be fixed and it cost this much, etc. 2 weeks time to repair.


5. "5) Does the price include machining the head if needed and if so what is included? new valves, etc, what?" Machining? Yes, They are taking it to a shop. So the labor is pretty extensive I believe. Another mechanic agreed and suggested to replace the engine with one with lower miles. A 'new' USED 07' Highlander or 400h engine from collision repair shop. We found an engine in Fresno for 1250., 07 Highlander 68k miles on it. He said it's easier to replace the engine than do these repairs. Plus, I get a engine with lower miles. I'm skeptical because it's such low miles.
quoted roughly the same, 3250. 2000 for labor.
6. 6) Plz provide a beakdown of the prices."

I really don't know and didn't ask.

7. 7) Most important- how was this diagnosed? If he pulled off the cylinder head to look as implied someone may be pulling your leg- they would've had to put new head gasket to get it back together already."
He did say it is unsafe to drive after he 'checked' things out and took it to another machining shop. I think it's because the gasket was leaking worse than before and may damage the engine?. What's your take? You think he pulled the head apart if that's what his advice is? Another mechanic said I could drive it a few blocks but not much more.


I've seen videos on how to diagnosis if the head gasket is really failing and leaking. From a Toyota mechanic's youtube channel.

It seems very invasive compared to them doing all sorts of maneuvering parts to diagnosed the p0300 code. But to be fair to them, they were looking for all reasons why the p0300 code was active.

Thanks,
David

That would be a togh call for me.
I may go with the low miles engine.
Warning- I've caught the salvage yard guys to by lying scumbags.

Last time I enquired for an engine for my car I called several places for"low mileage" engines and none of them could prove the mileage.
I believe the VIN is on the engine but if not the vin for the car it came out of can be ran, if they are honest about the VIN.
You can run the VIN on carfax if you are worried about getting a 200k miles engine that has been pressure washed and shined up. lol

PS- should add when I ran the car's vin on carfax the mileage came back over 100k more than what was told to me. I called the salvage yard and the guy shrugged me off and said that's what he was "told" so they have no conscience about bearing false witness.

I bought a car that was rolled back a good 70k miles than what it was supposed to be. 186 k. It's a piece of junk 2008 Jeep Patriot.
Now I always run Carfax on the used cars we buy and bring it to a mechanic.

Honestly, I'm skeptical about a 68k mile engine from a 2007 Highlander.

Then you need to pay up a bit more and go to a real yard, like LKQ. Most parts come with a free warranty of some sort. Using car-part, you'll be able to see pics of the car in question, so there's no worry.

Going to the no-name savage yard is a risk unfortunately, since they're chasing a sale and a bottom line. LKQ is so big, they don't have the time to screw someone over an extra 5$ on a sale lol

$1200 for a 156k Used engine for Highlander on LKQ. I can't find anything lower near my area. I