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Discussion Starter #1
Hello! Long time lurker & member at ToyotaNation. Looking to potentially buy a 04-10 Sienna for my next car, and cross-posted this at ToyotaNation:

I am considering purchasing a 3rd car for family trips, likely an 04-07 Highlander or 04-10 Sienna. Most that I am looking at have over 120K miles, which makes it due for the (big) spark plug replacement job. I would plan on keeping this car for 10-15 years until 250-300K miles, so I would like to only do this job once.

I know that the 1MZ-FE (3.0L) had a rubber coolant bypass hose, and I believe the 04-06 3.3L 3MZ-FE was the same. Does the 07+ 3.5L have this hose as well? Also, does anyone know if this is a Toyota-specific design - I was also looking at the Odyssey/Pilot/MDX with Honda's 3.5L and saw no such hose.

As I would like to open the spark plug area only once to save on labor costs, would it make sense to replace the coolant bypass hose while I already paid the mechanic for his labor? Or is this hose likely to last to 300K?

I would have the mechanic replace all 6 spark plugs, rear 3 ignition coils, and both valve cover gaskets. Probably the PCV valve too. But I am unsure about the coolant bypass hose. Anything else I am missing? I read that there are other gaskets to be replaced too, such as the intake manifold gasket an intake plenum gasket(?)

Thanks for any help. It's greatly appreciated!
 

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I recently repaired a very minute leak in the "valley" of my 06 Sienna. I replaced the bypass hose there as well new clamps. The parts man told me that those hoses are usually "lifetime " hoses and I don't doubt him at all because The original one with well over 15ok miles looked and felt really good. I agree with the spark plug change and the rest that you mentioned . Good luck
 

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I replaced my coolant bypass hose as well at around 120k miles. The original one looked like it can last another 100k miles. But since it cost <$20 on Amazon and I was in the area to replace the spark plug, I replaced it anyways. There are discussions on the forum where people encountered hoses that failed. Maybe those failed due to excessive temperature? I live around mostly flat ground. No mountains for excessive heat buildup. That is probably why it was in good condition when I took it out.
 

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You may also want to consider replacing the Thermostat and Thermostat housing. The plastic thermostat housing is know to crack. When I replaced mines, the condition looked good. Again, it is probably because my engine had a gentle life on the flat roads here in NY.
 

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Hoses also fail due To cavitation cause by not bleeding the coolant system throughly or running low on coolant. My plugs and hose are original at 205k miles buy a bad mechanical left the coolant 1/2 gallon short. Traveled 30 miles with it low at 100 k miles. Replace at two radiator hoses, thermostat Toyota oem and serpentine belt.
 

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Discussion Starter #6
I recently repaired a very minute leak in the "valley" of my 06 Sienna. I replaced the bypass hose there as well new clamps. The parts man told me that those hoses are usually "lifetime " hoses and I don't doubt him at all because The original one with well over 15ok miles looked and felt really good. I agree with the spark plug change and the rest that you mentioned . Good luck
Do you have any concerns with the other coolant hoses (i.e. heater hoses)? Thanks for the feedback!
 

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Discussion Starter #7
You may also want to consider replacing the Thermostat and Thermostat housing. The plastic thermostat housing is know to crack. When I replaced mines, the condition looked good. Again, it is probably because my engine had a gentle life on the flat roads here in NY.
Yep, I saw that the thermostat housing was plastic so it seems like it should be replaced as well. I was wondering if you had any concerns about the smaller coolant hoses like heater hoses, given that you replaced the coolant bypass hose early?
 

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The upper radiator hose wears out first. The heater hose does get that must flow, so latest a long time (15 years with 205 k miles and still going) New rubber (Edam?) Hoses are very long life. The Toyota spring clamps also makes the hoses last longer too.
If the end of the hose at the nipple is worn, it can just be trim off in a pinch. I had to do that on another car due to cavitation (it also wore 1/2 of the aluminum elbow.
 

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Do you have any concerns with the other coolant hoses (i.e. heater hoses)? Thanks for the feedback!
I only replaced hoses that would require an extensive take apart to get to. In addition to the bypass hose there was just one other that I replaced. Forgot which one it was but it had a rubber shield around it. Nevertheless the old one still looked and felt good after 13 years and 169k miles.
 

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You can change the valve cover gaskets, spark plug gaskets in the valve cover, plugs, PCV valve - VVT valve screens and the Hose/Pipe on the Thermostat - the Knock Sensor Wires as well. Your knock sensors usually are ok and the wires get shorted.

Hello! Long time lurker & member at ToyotaNation. Looking to potentially buy a 04-10 Sienna for my next car, and cross-posted this at ToyotaNation:

I am considering purchasing a 3rd car for family trips, likely an 04-07 Highlander or 04-10 Sienna. Most that I am looking at have over 120K miles, which makes it due for the (big) spark plug replacement job. I would plan on keeping this car for 10-15 years until 250-300K miles, so I would like to only do this job once.

I know that the 1MZ-FE (3.0L) had a rubber coolant bypass hose, and I believe the 04-06 3.3L 3MZ-FE was the same. Does the 07+ 3.5L have this hose as well? Also, does anyone know if this is a Toyota-specific design - I was also looking at the Odyssey/Pilot/MDX with Honda's 3.5L and saw no such hose.

As I would like to open the spark plug area only once to save on labor costs, would it make sense to replace the coolant bypass hose while I already paid the mechanic for his labor? Or is this hose likely to last to 300K?

I would have the mechanic replace all 6 spark plugs, rear 3 ignition coils, and both valve cover gaskets. Probably the PCV valve too. But I am unsure about the coolant bypass hose. Anything else I am missing? I read that there are other gaskets to be replaced too, such as the intake manifold gasket an intake plenum gasket(?)

Thanks for any help. It's greatly appreciated!
 

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Discussion Starter #11
You can change the valve cover gaskets, spark plug gaskets in the valve cover, plugs, PCV valve - VVT valve screens and the Hose/Pipe on the Thermostat - the Knock Sensor Wires as well. Your knock sensors usually are ok and the wires get shorted.
Thanks for the info. That is the first time I have heard of replacing the knock sensor wires. Is it a common issue?
 

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Thanks for the info. That is the first time I have heard of replacing the knock sensor wires. Is it a common issue?
Yes the Knock Sensor wires is a common issue - typically when the knock sensor codes are thrown - the answer is not the sensor but the wires. When you see how they are routed - you can get the understanding why this happens to them. You can check You tube - I think the computer code is p0328 , you might be able to see a pending code. Thing is once you have all of that stuff out of the way - a one time deal to get a 100-150K out before doing it again .. not a bad thing.
 

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Discussion Starter #13
I only replaced hoses that would require an extensive take apart to get to. In addition to the bypass hose there was just one other that I replaced. Forgot which one it was but it had a rubber shield around it. Nevertheless the old one still looked and felt good after 13 years and 169k miles.
Hi Paul,

Thanks for your response! I'm looking at the procedure to change the spark plugs and it seems doable, although difficult. I have a question for you: I watched a YouTube video on how to change the rear valve cover gasket, and the mechanic went underneath the car to loosen the three metal support bars that hold onto the intake plenum - these are are the three bars which the three most difficult screws to get to are attached. I think you know which ones I'm talking about, the left-most one houses the dreaded 14mm screw, the right most one attaches to the throttle body (I think), and they are right in front of the firewall.

My question is: did you have to loosen these in order to get the valve cover off the car (so that there would be enough clearance to get the cover off), and if so, would I be able to loosen these from the top of the car? Jacking up the car and climbing underneath it is something that I would prefer not to do.

Thanks for your help!
 

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Its been a while now and I cant remember if I had to remove those screws. Actually Thinking about it now I believe you have to, as that bar is what helps to support the intake plenum which must be removed. The right one which supports the TB is not as bad to remove. When tightening up the support bar that has the 14mm it is helpful to loosen up the associated nuts on that assembly and the only way is from under the van.I understand fully about going under a jacked up vehicle but trust me I have extra jacks and jack stands strategically located to support the van while I'm under. My cell phone is always in reach also.
PS. I will double check to see if I am giving you good info. Will respond soon
 

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So I took a look and it seems you have to undo that dreaded 14mm bolt . Upon reinstallation it is very difficult to get that bolt back in without having to loosen up the other nuts from under the car. This gives that bracket a bit of free play which allows you to get that 14mm bolt in. Hope this helps
 

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The plugs are easy enough - I have done them twice. I recommend that you change everything you can (feel should be a serviceable part) while you are in there. It is not one of those jobs like in the old days - 4 plugs 15 minutes and done. I think once you are in there - changing coolant bypass hose (pay attention to coolant droppings - if you have the pink stuff - it will look like a pile of pink fluffy stuff) , knock sensor wires , intake manifold gaskets, plenum gaskets, vvt screens, pcv valve and plugs - Valve cover gaskets - pay real close attention on re-installing the gaskets - make sure that the rear is on look from underneath and the top. You will be happy that you did the work and got it all done.
 
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