Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

I've fallen behind on Maintenance

It’s true. I’ve fallen way behind on maintenance for my 2007 Toyota Highlander. Now, I’m trying to figure if I need to do anything different to help “catch up” and save any vehicle components.

  1. The service guide recommends that I “replace engine coolant” at 100k miles, but I never did. I’m now at almost 180k. Does Toyota mean a drain & refill, or a flush? Since I’m overdue, is there something else I should do to the coolant system? (The engine temperature has been steady since the day I bought it used, so I assume I don’t have major cooling issues.)

  2. The guide also recommends replacing the spark plugs at 120k. I’ve read multiple websites that list symptoms of needing new spark plugs (starting problems, rough idling, etc.), but I have none of those symptoms. Should I wait for a symptom, or pre-emptively replace the plugs?

  3. The guide does not mention replacing transmission fluid. They just recommend inspecting it. Should I replace it? (I have noticed that changing gears is not as smooth as it used to be.)

(For what it’s worth, I’ve gotten the other items done - replaced air filters, changed engine oil and filter every 5k miles.)

I’d appreciate any advice. Thanks!

I would drain and refill unless the coolant looks really bad

Yes replace them, make sure they are the exact OEM plugs in the same brand as original (this will be in your owners manual)

This is an unfortunate effect of manufacturers trying to make their cars appear to be as maintenance free as possible. Most posters on this site recommend every 30k miles. I would do a drain and fill, then repeat the procedure in 500-1,000 miles


You don’t want to wait to have symptoms. Get them replaced now. Denso and NGK are oem plug manufacturers for Toyota. Use either one, and make sure it’s the same type of plug. My 05 4runner came from the factory with NGK plugs on one bank and Denso on the other bank. And I wasn’t the only one with this setup. I replaced all plugs with NGK. Don’t use plugs from any other manufacturer.


+1 to the preceding comments/recommendations.

As to…

To try to relate this to human terms, do you think that middle-aged to elderly people should have a Colonoscopy performed every 5 years or so, or should they wait until they have symptoms of Colon Cancer?

You can inspect your plugs. However, they’re so cheap if you do it yourself, you may as well.

given that the engine has 180k on the clock and they’ve never been replaced, when you get them out, put new ones in!


Also if you replace the plugs it will “probably” be the last time you will do it … Chances are you won’t have the car in another 130-150000 miles .

1 Like

That means replace ALL the coolant. Not just some of it.

This would require draining the engine block in order to replace all the coolant.

I would get it flushed. This replaces all the coolant without the mess.

Here’s the machine I use.

If there were a problem with the spark plugs, the Check Engine light would on with misfire codes.

For what it’s worth, the spark plugs in my 97 Accord have 220,000 miles on them and the engine runs smooth.

When it comes to transmission fluid service, I tell people to read this.


My '95 Avalon came the same way. NGK on one bank, and Denso on another.

(I’m the OP - just with a new name.)

Thank you all for the input! I think I’ve got my work cut out for me.

I would have replaced the spark plugs a long time as they are generally so cheap, but in the 2007 Highlander V6, it turns out that half of the spark plugs are difficult to get to. The Toyota deaership quoted me around 5 hours and $480 to replace them. So I was really hoping you all would say don’t worry about the spark plugs as long as everything is running smoothly. :wink:

Those are good tips on ensuring the spark plug manufacturer is OEM and consistent. Thanks!

Thanks for the info. (By the way, I think it’s interesting that your machine is for flushing the coolant, yet the machine name is “Drain & Fill”.) I may have misunderstood, but isn’t “flushing” where you use a pump to force liquid through the coolant system to push out any solids?

The coolant should definitely be replaced. It gets more and more acidic with time and miles driven. Eventually it becomes so acidic it starts to corrode the engine’s internal parts. The more of the old coolant you can get out, the better. When I do that job on my vehicles I drain as much as comes out the radiator drain plug, then just refill with run plain water and run that through the system for 10-15 minutes, then do a simple drain and re-fill w/fresh coolant. That gets most of the old coolant out. You may run into some problems extracting the spark plugs since they’ve been in there so long. The threads of the plugs can sort of bind to the cylinder head’s threads. When the plugs are removed the cylinder head’s threads can get damaged during the removal. So double check to see if that’s happening as part of the process. If it does you’ll have to get some machine shop help. I’d replace the transmission fluid & its filter (if applicable) too. From what I’m seeing the V6 version of that car uses a timing belt. If that’s the engine you have, that’s another service item that probably needs attention. Be sure to use the correct replacement fluids all around. Buying the refills at a Toyota dealership makes a lot of sense imo. If you are doing all this stuff yourself, don’t get overwhelmed. Just do one job at a time.


The process of replacing a contaminated fluid with clean fluid?

Like flushing the toilet?

Yeah. That’s what it does.