What I thought was gonna be a simple quick job ended up being. Not that. Recently I got an 04 clk500 with 100k miles on it I've been swapping parts that I deemed as you know maintenance items since the mileage is high and I can't be sure what was done previously. Spark plugs, air filters, bushings, shocks, new intake pipes etc, and today was the thermostat, and temperature sensor I was going to tackle.

I ended up deciding I was going to drain and flush the coolant as well since it was looking a bit cruddy. We'll I've done that now new thermostat is on, new temperature sensor is on, and did 2 flushes of the coolant system with distilled water. Now I am almost positive I have air trapped in the system that I'm unable to bleed properly. I've lost heat where I previously had it, at least from the defrosters. The main vents were always cold but I believe that's something with the blend door and the clicking I hear which from what I understand is a common issue. The temp gauge will go to about the hash line between the 80c mark and the 120c mark and just stays there.

Cooling fan comes on full blast the expansion tank will sometimes overfill and boil over other times it'll be near empty. All without me doing anything other then having the cap off to burp bubbles. I've squeezed the top radiator house going to the thermostat housing and it feels like there's no coolant that's made it's way up to there. (this while the car was hot and running)

So I'm asking for advice, before I purchase a vacuum filler to drain it properly and fill it properly, on what I've done wrong to this point?

II will add that the temp sensor is an ngk branded one not sure if that'd give a false reading for the temp gauge as to why it's not doesn't move once up to temp

 

With heater at max temp and full blast the aux water pump should be running. If it’s not, you need to look into it and perhaps replace it. It sits right up against the coolant reservoir. Listen to it and if you can remove it and test it by applying 12 volts to it. Also feel the hose out of the aux pump running towards the interior. If it remains cold, the pump is not running or failed.
Another issue (quite rare) the valve in the thermostat may be tilted and out of alignment. This can happen if you drop the thermostat. Misalignment can prevent the thermostat from opening completely.

I vacuum fill the system. But encountered a failed aux pump that drove me nuts since it was working until I flushed the coolant, changed thermostat, upper radiator hose, water pump, pulleys and belt.

good luck.

 

I'm assuming that's the little cylinder that hangs off the side of the expansion tank? I'll definitely look into that I never even thought of that my old Saab never had one so it's also just something I never learned about lol but I've ordered a vacuum filler because I really think it's air I'm not getting out but if that doesn't work I might throw the old thermostat back in to see if that ends up fixing it. I was more so worried that my new temp sensor was wrong and my car was in fact overheating and the water pump had failed or something crazy.

 

Yes, that’s the one hanging from the expansion tank.
i did vacuum fill the engine twice, then checked the aux pump only to see that it had failed. Replaced it and all was good (actually I replaced the expansion tank as well, since the cap can fail over time).

water pump spontaneous failure is unheard of (unless you can see it leaking, making noise or the pulley wobbling).
Checking errors via scanner is also a good thing if you have access to one.

My car has 170k mikes on it and I’ve done two major services on it each after ~80k miles. These engines are as solid as they come. They well designed and there are procedures available online which make life easier.
if you just bought this car, don’t neglect the transmission service. The “life time transmission” oil typically in the owner’s manual is total BS.service the transmission right away if it has not been serviced already. I do it every 60k miles minimum.
Just take your time, use OEM parts and procedures, and you’ll be fine.

 

So I'll look into getting an auxiliary water pump and just replace it since I can get one relatively inexpensive water pump does seem to be working fine fluid did move through the expansion tank when doing the cleaning as in the water went from clear then junk moved into it while it was running no leaks that I've ever saw or smelled never lost coolant til this point so I'll rule that out as well for now.


Thank you for the advice as well I did follow some threads on here before I did it that said the system self bleeds and the way I did it wouldn't be an issue but it seems to be an issue so I do think a vacuum fill will resolve the issue along with the new auxiliary pump will follow up when I get a chance this coming weekend or next.

Also on the transmission according to the previous seller it was rebuilt not long ago and I thought the 5 speed was pretty much bullet proof but I'll start looking into doing this as well better safe then sorry!

 

Just wanted to follow up and say a simple vacuum fill resolved the issue. Definitely seems more finicky when it comes to bleeding itself compared to my Saab but its a lesson learned and new tool added to the arsenal .