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Discussion Starter #1
I have a 2007 RAV4 Sport 6cyl with 200k miles. About a year ago, it started to "miss" -- I also noticed that it had a tendency to overheat while idling on hot days.

I started by replacing a faulty ignition coil, which seemed to help for a short time. I then took it in to address the overheating issue. The shop replaced the coolant overflow tank, which they said had a leak. This also seemed to help for a short time. But, probably a month later, it started to miss and run rough again, but this time with a bad rattling sound, and the tendency to overheat on hot days became an issue again.

Long story short, I ended up replacing the waterpump and the other 5 spark plugs and ignition coils. When it left the shop, they advised that they couldn't seem to locate the problem of why it was missing -- they left the car running for over an hour and said it seemed that it was running fine.

About a month later, it seems to be "missing" again, but nothing is showing up when I run a diagnostic on it. And it still wants to overheat when it's idling on a hot day.

One other symptom that people seem to be blowing off, but I think is connected in some way ... my outside temperature indicator has been showing readings that don't seem to make sense. If I'm driving, or when I'm first parked, the outside temperature seems to be accurate. But after idling for a few minutes, all of a sudden the outside temp shoots off the scale (it shows "--"), but the oil temperature will still be showing normal -- at least at first. Once I start moving again, the outside temperature starts falling down to an accurate reading, and if the oil temperature was also high, that will fall back down to a normal reading as well.

After doing a lot of research, I'm wondering -- does this sound like the head gasket is failing? I'm wondering if, as the temperature rises while it's idling, maybe the head gasket is failing in a spot and causing an area of the engine to become hotter than it normally would be, which happens to be close to the outside temperature indicator. Since I'm neither a mechanic nor an engineer, I could be completely wrong ... who knows.

Anyone have any thoughts?
 

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When you ran the diagnostic, which if any codes came up? Also, you mentioned an oil temperature gauge - do you have one, or did you actually mean the coolant temperature gauge?
 

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'06 & early '07 V6s may have multiple coil failures multiple times. I've used 10 replacement coils on ours, one just a couple weeks ago. But they always triggered the CE light and gave a code for the bad one.

The outside temp sensor will definitely read high in error while the car is parked idling due to no flow of ambient air. If that's how you're judging "overheating at idle" you don't have problem.

If it truly is overheating due to a failing head gasket you'd likely also be losing coolant.
 
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2008 RAV4 Limited V6
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It sounds to me like your electric fans might not be running, or maybe only just one of them. If it's fine at cruising speed, that's because plenty of air is flowing through the radiator and the fans aren't needed. With the A/C on, both fans should be running.
 

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No codes show up -- either at the shop, or when I've done it myself. Before I replaced the coils, I had a code show up, but none now.

Also, my bad -- coolant temp, not oil temp.
 

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Discussion Starter #6
Also, fans are working fine -- the shop checked them all out ... they're the ones that suggested a possible problem with the head gasket, but I wasn't ready to run any diagnostics for that at that point -- might have to now.
 

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I don't recall a confirmed case of a failed head gasket on a V6 engine but then none have had 200K miles either. If it's causing a miss a compression test would confirm it but that involves pulling all the coils & plugs - not a simple procedure on the rear cylinders. And, altho it's possible to have one of the head gaskets fail w/o any coolant leaks, usually coolant loss is the first symptom.
 
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