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Has My Thermostat Gone?

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Hey guys,

I'm new to this community but it seems like a great place to get to know people. If only I had come across this site when I got my first Lexus a few years back.

Anyway, I digress...I currently have a 2007 IS 220d that's developed a fault. I've noticed that it's stopped pushing out hot air through the fans, whether it be with the A/C on or off. If I go a little faster, say 50MPH or more (motorway driving for example) then a little hot air gets through but certainly not the normal amount.

This morning on my drive into work (around 20 or so miles on the motorway) I noticed that the temperature gauge was creeping up, it got to around 3 notches away from the "red zone" then started to fall back to normal levels. After which it started to rise again.

I assume that the fluctuations in the engine temperature is due to the fan kicking in in order ot cool the engine when it gets to hot. This couple with the lack of hot air coming in leads me to believe that the thermostat may be shot on the car. I've also done some research on the heater problem prior to this morning (which is how I found this site) and I believe a blocked heater matrix is common on the 220.

So, after my very longgggg story I was wondering if anyone has had any similar symptoms on their cars and what the cause was?

Thanks in advance ladies & gents.


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I'm purely guessing as I have no experience in this area but if you say your temp gauge went up higher than normal indicating over heating, engine not getting enough cool water to it and also coupled to the fact you don't get heat from the Heater fans when clearly you have a warm engine it certainly sounds like a blockage.

I've not heard of the matrix blocking but if this was the case and water was not circulating properly then your experience would certainly sound about right.

I'm sure someone more knowledgable in this area will come along shortly.


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I thought that might be the case, nice to see that others are following my rationale. I've already ordered a replacement thermostat, since they're so cheap and it's a quick job to replace it, I might as well.

Pending any other replies from other members, I'll let you know how I get on.

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The thermostat is a good place to start, if it is stuck open the engine will take a long while to reach normal temperature and if stuck closed will cause overheating and poor heater function as the coolant flow will be limited to just the engine block and radiator.

Easy to confirm a faulty thermostat, grab a Pyrex jug fill it with freshly boiled water then with the stat suspended on some wire or string lower it into the water, if it is working you should see it open, if it doesn't it's faulty.

If the thermostat is not the cause you may have to consider a faulty water pump as the cause, if this fails you will have poor water circulation leading to overheating.

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Have you changed your pollen filter lately? If its not done correctly the small actuator that controls the flaps inside jams.

It can also happen if something thin has got into the unit (like a cd in my case)

If you turn to completely cold then warm, you may hear it clicking if its popped out, rather than a smooth flow type sound.

I can't remember if I could get to it when I took my glove compartment out or I had to go from the footwell upwards.

** if you are checking your filter, follow the procedure in the manual as the heater has to be in a certain position the release the filter tray!

This doesn't explain the engine running slightly warm but possibly a different issue.

Just throwing ideas in case its not the thermostat.

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Thanks for all of your comments guys. The good news is that I've fixed the issue, the bad news is that I'm really embarrassed that I didn't look at it sooner.

So last night after work I decided to spend some time working out what the problem was. I had already checked my oil for water and it looked fine so I don't think it's the head gasket (should have mentioned that in my original post, sorry!). So I then took the thermostat off and looked at that - it was fine too. So finally, I had a look at the heater matrix (yes it was a late night!) that wasn't clogged and seemed fine.

At this point I was at a bit of a loss as to what the problem could be. On a whim I looked at the water reservoir and it was completely empty, bingo! So I nipped down to the local garage, got myself a couple of bottle of anti-freeze, filled the sucker up and took it for a test. Instantly there was lovely warm air flowing through the cab. On my way into work this morning the engine temp was also fine.

I'm obviously going to keep my eye on it over the next few days as the system must have emptied somehow. Probably a cracked hose or something. I'm really relieved to find that it's something so simple, I was clearly just over thinking it.

Thanks again for all the help guys, I really appreciate it.


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HI Kev , finally i have just read an answer to this problem !! i have had the exact same issues , was fine during the summer but this time of the year is a disaster, driving down a cold foggy motorway this morning the fan had barely cleared my windows half way up - not to mention the side windows completley misted !!

working in IT im pretty useless when it comes to anything other than driving my motor or pressing a few buttons on a KB:) i'd be gratfeul if you could help in the hope i'm not sounding ridiculousy stupid

what and where is the water resevroir, and do i need a particular type of ant freeze

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The water reservoir is just behind the rad when you open the bonnet. It's clear plastic and cylindrical with a black screw careful opening the screw top!! Do it when cold. Buy some antifreeze from your local Lexus dealer if you are not sure what to get.

Fellas if you are losing liquid you need to find out why...and quickly!! Do check for any signs of oil droplets in the water and keep an eye on the oil on the inside of the oil filler cap. You DO NOT want to see any white mayonnaise like residue there!!

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What Normski said :)

I also work in IT funnily enough. However, except for the last two I've owned (my Lexus obviously, and previously a Honda Civic) they've always been old bangers so I've done all the work on them myself. Luckily it means that I've got a fairly good grasp on cars.

Just as an update, my motor has been brilliant for the last 3 days now - lovely and warm in the mornings and hasn't even got close to over heating. I'm off work for a few days after today so I'm going to strip the cooling system down and service all the hoses. If any are broke/degraded then I'll fit replacements. I'm really glad it's nothing big like the heard gasket. Didn't fancy stripping the head down myself on this car!

Good luck "LexusLusher".

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Kev...if you are the least bit mechanical, please get to grips with how to clean the EGR valve. It really is important. It's really very easy, once you have done it twice you will be able to do it in 25 mins tops. There are a lot of posts and vids on here showing how to do it. Also, while it's off clean the port to the inlet manifold and have a hoover going at the time to suck the crud away as you scrape it out. Oh.. and do this every 8000 miles or so just to be safe!

The only tricky bit is the lower bolt on the EGR pipe round the back of the head block. Get a short enough extension that does not make your socket wrench foul the side of the Battery casing. You will need to undo both of these bolts to get the stainless pipe off..whicvh allows the EGR to be removed. Don't be tempted to bend the pipe up you may damage it big time.

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Hey thanks for the replies ! i took the bull by the horns and opened the bonnet and found the water reservoir myself (wayhey) it was completely empty - so filled only with water to the line. was in work basement so couldnt get my hands on any anti freeze ! what i would say is it did heat up a little quicker but the fan level at max is still totally useless ??? i would say in comparison its on par with the first fan notch of my previous is200.

another point to add is -my car generally runs 24/7 with the AC button on and during the summer months the AC does cool the car slighlty but again nothin on par with the good old IS200 sport i had for 7 years and never a thing wrong :)

what a motor that was :)

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Make sure you add anti freeze... if you put a fair amount of 'water only' in you will dilute the anti freeze mix. The last thing you want is a frozen cooling system.

Never had to do this so I can't speak with any authority on the subject...but maybe the heater matrix will need bleeding to remove any trapped air? Maybe that is why you struggle to get heat thru into the cab. Just a thought.

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