B8.5 A4 2014 Help with coolant temp sensor / Intake air system

[moieser]

was driving, car overheated and said to keep engine running but stationary.. did that, engine temp dropped all the way to cold so i guess thermostat was stuck open.. no heat in cabin so i expected heater core clogged or something. got home. i changed and flushed coolant out and noticed oil in coolant resovoir when i did.. I flushed one side of the heater cose hoses, little heat in cabin then, but just turns back to cold..(bled the air out, still cold) i did research people saying elsewhere might be head gasket or pcv valve breather assembly, shop wanted a lot of money.. 150k miles on the car. recently did oil change with liquimoly 5w-40 couple hundred miles ago.. not much oil consumption with this car so far only sometimes 1qt between changes
codes are
P0117 - Engine Coolant temperature circuit low
P2279 - Intake Air System Leak..

any help really appreciated wondering if i should just replace that sensor or get a new pcv valve.. or both.. even head gasket? really concerned i'll be putting in more money than i expect and i don't want to be screwed by shops either.. thanks ahead of time.

[Smac770]

"i guess thermostat was stuck open", overheating would not imply that at all. The coolant temp not reaching normal range would imply that.

If the coolant temp sensor is toast, you should certainly replace it. Engine is going to be all kinds of not happy with it given wrong data. But is it the sensor or the wiring.

P0117 is set if the reading from the coolant temp sensor exceeds 140°C. If you read the coolant temp measuring value from the ECM, what is the reported coolant temp? 140 would be a short to ground, or bad sensor.

So you might have an intermittent wiring failure, or you might have a failing sensor. If you unplug the sensor, the reported temp should go to -40°C. If you short the two pins on the harness plug together, the reported temp should go to 140°C.

If the engine has sat overnight so the sensor should be at ambient temp, whatever that temp is (in the car location space, not necessarily on the weather report), you should measure the resistance across the sensor pins. In spec is:

5°C, 4443-4970Ω
15°C, 2923-3235Ω
25°C ,1978-2167Ω


The ECM cuts off the coolant flow to the heat exchanger via the N422 coolant shutoff valve, which is electrically operated in B8.5. That state of that valve in the J255 HVAC measuring values would be of interest. Are the hoses to the heat exchanger hot or cold?

P2279 and a PCV are unrelated topics. You have some issue causing a P2279, but whatever it is, that's a separate analysis.

I had some darkness (dirt, oil?) end up in the coolant tank top wall but have left it be and it's been fine. Maybe some coolant/oil mix in the oil cooler, maybe a head gasket temporary issue, who knows. But my heat works fine, so I don't have an issue I need to resolve involving the coolant system.

[moieser]

so the day after i changed the coolant, drove the car for about two hours and its not overheating anymore. codes all went away on their own and didn't come back, so is it still a good idea to replace the coolant temp sensor? if so where is it? i drove it an hour after i bled the heater core hoses to try to fix the heat in cabin. the coolant doesn't flow really fast through those hoses though. but i noticed how now heat only gets into cabin if engines above idle rpm's. so when rpms are higher could that be why im getting moreheat into the cabin because of more coolant flow to the core hoses? im new to working on this stuff and honestly try to research it as much as possible and on youtube it's hard to know whats right.. not many videos on b8.5 coolant temp sensor replacement either, so my experience is very minimal at the moment but im learning.. thank u for the advice [mention]Smac770 [/mention]

[mc_hotmail]

The coolant temp sensor is cheap. Since it is a suspect, I would stock one. Yeah, it's a kind of hassle to replace just the sensor, because it is blocked by the throttle body and a few coolant pipes. Small hands help.

[StuckAntichris]

The sensor is located on the waterpump housing. If you look up a waterpump replacement guide/video you will see it located on the upper left corner of the housing. You could get the sensor replaced without removing the pump housing however you may be halfway to a water pump replacement at that point.

If you dont have a record of the pump being replaced, it will leak at some point. Would probably be worth the money to replace the pump and the sensor at the same time.

[moieser]

The coolant temp sensor is cheap. Since it is a suspect, I would stock one. Yeah, it's a kind of hassle to replace just the sensor, because it is blocked by the throttle body and a few coolant pipes. Small hands help.

You think the coolant temp sensor is causing insufficent heat in cabin? Engine holds correct coolant temp now after i replaced coolant and bled the system along with one heater core hose (left) i just dont have heat in cabin now.. unless above idle

[StuckAntichris]

when the engine is at operating temperature and running are either of the lines running through the firewall warm/hot? If neither hose is hot they you do not have enough flow. There is a hard line coming out of the water pump going to one hose and the other hose goes to the head. It is very possible that you have a thermostat issue or that something in the water pump has failed.

[moieser]

when the engine is at operating temperature and running are either of the lines running through the firewall warm/hot? If neither hose is hot they you do not have enough flow. There is a hard line coming out of the water pump going to one hose and the other hose goes to the head. It is very possible that you have a thermostat issue or that something in the water pump has failed.

dang their cold so best option is to replace waterpump/thermostat assembly.. is it safe to drive


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[StuckAntichris]

It is safe to drive as long as your engine temperature does not go outside of normal range. Before you throw a water pump at it there is actually a hole in the top hose right at the actual firewall. You will have to take the rain tray out to see it. You can pull the hose off of the barb a bit in order to bleed the system. DO NOT DO THIS WITH THE ENGINE WARM OR YOU WILL BURN YOURSELF AND GET COOLANT EVERYWHERE

If you are not comfortable doing that you can wait for the engine to cool completely and just warm the engine up with the coolant cap off. With the cap removed start the car and rev the engine to about 2000 RPM and back down to idle a few times, maybe you just have a stubborn air bubble in your heater core.

[moieser]

It is safe to drive as long as your engine temperature does not go outside of normal range. Before you throw a water pump at it there is actually a hole in the top hose right at the actual firewall. You will have to take the rain tray out to see it. You can pull the hose off of the barb a bit in order to bleed the system. DO NOT DO THIS WITH THE ENGINE WARM OR YOU WILL BURN YOURSELF AND GET COOLANT EVERYWHERE

If you are not comfortable doing that you can wait for the engine to cool completely and just warm the engine up with the coolant cap off. With the cap removed start the car and rev the engine to about 2000 RPM and back down to idle a few times, maybe you just have a stubborn air bubble in your heater core.

Okay i will do this and make an update after, im wondering about both hoses. left hose has a hole i know this, but should i backflush it with warm/hot water too? or just bleed it, seems like there was some chunky stuff after coolant change maybe stopleak preventing flow.. otherwise yes, engine holds correct coolant temps when driving


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[Theiceman]

i have drained and filled many a4s of different engines. 3.2 various revisions . i have never once had to mess around with that bleed hole ever..

getting that thing off you could do more harm than good . it is bonded on there over the years i'm sure.

[StuckAntichris]

Now that we know that there was some chunky stuff in the coolant, you should flush your heater core and make sure it is not blocked.

I agree with Iceman, I would not mess with the bleed hole until it is your last option. You should ensure that the cooling system is free and clear before proceeding with replacing parts since distilled water is cheap.

[moieser]

Now that we know that there was some chunky stuff in the coolant, you should flush your heater core and make sure it is not blocked.

I agree with Iceman, I would not mess with the bleed hole until it is your last option. You should ensure that the cooling system is free and clear before proceeding with replacing parts since distilled water is cheap.

How do I bleed the coolant system in the b8.5 properly


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[moieser]

There was a ton of air in the coolant system (Just held hose and squeezed) let it all out, kept topping off the coolant resovoir tank with cap off. Put ac on and heat on max, revved car to 2000 ish, let the heater core bleed air, and heat was back in the cabin.. Coolant temp is good, when heats on its a little lower than the middle which i read up was normal in colder temps. I'll see tomorrow if the level drops any or if the heat continues to work.. thanks all for the help.


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[Theiceman]

fill it up.... start it ... if it goes down keep filling... drive it around top it off after engine cools down. I've done about 4 with no issues

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[Theiceman]

There was a ton of air in the coolant system (Just held hose and squeezed) let it all out, kept topping off the coolant resovoir tank with cap off. Put ac on and heat on max, revved car to 2000 ish, let the heater core bleed air, and heat was back in the cabin.. Coolant temp is good, when heats on its a little lower than the middle which i read up was normal in colder temps. I'll see tomorrow if the level drops any or if the heat continues to work.. thanks all for the help.


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it will be down tomorrow. top it off .

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[moieser]

it will be down tomorrow. top it off .

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will do, thanks.


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[moieser]

fill it up.... start it ... if it goes down keep filling... drive it around top it off after engine cools down. I've done about 4 with no issues

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what do you mean about 4?


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[Theiceman]

what do you mean about 4?


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rebuilt 4 engines so had to fill from scratch ..
no issues just filling it up and letting it gurgle.

[moieser]

rebuilt 4 engines so had to fill from scratch ..
no issues just filling it up and letting it gurgle.

i just topped it off, its in between min and max now level surface... is driving it just having it burp all those air bubbles out? havent had any codes pop up yet..


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[Theiceman]

yup you I'll be fine.. just put it to max coolant

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[moieser]

yup you I'll be fine.. just put it to max coolant

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not in between? just max?


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[Smac770]

Wherever between min and max when cold is in spec.

[mc_hotmail]

not in between? just max?

The point of several folks here is that the system produces sufficient pressure to bleed itself - forcing air back to the reservoir. Filling it to max ensures that even when a large amount of air got back to the reservoir, you still have enough coolant left (above min).

Yeah, I remember that bleed hole with a 10mm bolt in my 3.0L wagon. It doesn't do a thing. I unscrewed that bolt, preparing to see coolant coming out while filling the reservoir, but nothing came out.

[Theiceman]

setting it at the max line makes it easier to see if it starts going down

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[moieser]

setting it at the max line makes it easier to see if it starts going down

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ah i see. bad timing for all this to happen there's a blizzard where i am so im waiting for weather to clear up before poking around the coolant temp sensor


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[moieser]

setting it at the max line makes it easier to see if it starts going down

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Kept topping it off, no more coolant loss and there's heat in cabin now

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[Theiceman]

perfect ... you are good to go ... no other procedures required than just topping it off.. great work.

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[moieser]

perfect ... you are good to go ... no other procedures required than just topping it off.. great work.

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thanks man

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