PDA

View Full Version : Coolant temp sensor question?



Poopie
03-24-2006, 02:21 PM
I've been having hessitant starts lately. Takes about 20 seconds to fire up slowly and I have a high idle. Well today it happened and I popped the hood to see what was up. I knew the coolant sensor is on the fritz so I check that first. I checked the connector and widdled and the idle immediatly came down. I looked at my dash and the coolant temp read correctly. I think I just have a connection issue with the plugs or something. I wiggled it some more and looked at the dash again and my temp dropped to zero. I turned off the ignition, waited a minute, and tried to start again. Same thing, hesitated for 20 seconds and then slowly cranked over with a high idle. Wiggled the sensor and the idle dropped, looked at the dash and coolant read correctly. I sprayed it with contact cleaner/lubricant and we'll see how that holds up. I started the car again and it turned over normally and the coolant temp is normal. So my question is, how is the coolant temp related to the ECU? What does the ECU do when the coolant temp is cold? My gas mileage is crappy as well so maybe this factors into it too.


I also sprayed the shit out of my cruise control stalk and now it works kinda.

mike-2ptzero
03-24-2006, 08:54 PM
The ecu has a set coolant temp that makes it switch from cold fueling(choke) and warm fueling. If the ecu thinks the temps are below that reading it will never get out of the choke mode.

Poopie
03-24-2006, 10:52 PM
HOLY SHIT. No wonder. I tried to replace the sensor twice and both times i got the wrong one. First time from ecs, second time from pepboys.

mike-2ptzero
03-24-2006, 10:58 PM
Originally posted by Poopie
HOLY SHIT. No wonder. I tried to replace the sensor twice and both times i got the wrong one. First time from ecs, second time from pepboys.

Is the problem the sensor or the connector that you plug into the sensor? Better off just going to a VW or Audi dealer for the correct part, you can even get the part number off of the ones on your car.

k0mpresd
03-24-2006, 11:03 PM
you probably ordered the cheap green one from ecs

no telling what pep boys gave you

if you are a '98 you need the square blue type coolant temp sensor

Poopie
03-24-2006, 11:04 PM
I'm not to sure. I think the sensor is fine. I think the problem is in the connection since when I VAG it is reads intermittent signal. First time ECS sent me the green 4 pin on, then pepboys sent me some 2 pin shit. I need the 4 pin blue square sensor. I'm just gonna replace it and see what happens. When I wiggle it I can get it to read the temp. In cold weather when sitting in traffic the needle will point in the middle straight up. Then Highway cruising it will drop one tick from center. So I know that the coolant sensor is working. Sometimes it just doesn't want to work.

hoonee46
03-25-2006, 02:35 PM
About your coolant temp dropping at highway cruising... seems like your thermostat is stuck open. I second what Mike said 100%. So when you wiggle it, it works... so do you know what part of the sensor is malfunctioning? are you going to change that tiny spec of a part? where will you find it?? Are you going to wiggle that sensor every time you need a reading? of course not! just get a new one and be worry free!
that starting problem... it always happens? even when the motor is totally cool? I ask this question because with ECTsensor problems, it usually happens worse when the motor is warm... The thermostat thing is a problem because the ECT reads an incorrect reading (although it's functioning properly, it will read incorrectly because of the thermostat), sending it to the ECU. It will think the motor is cooler than it is, causing it to run rich/lean. Running rich will bring down your gas milage for obvious reasons.

Poopie
03-25-2006, 03:12 PM
Yeah I know, I'm gonna get it replaced. I'm just too damn lazy to order off ECS. What does the dealer charge for the part? Its the 4 pin blue connector.

hoonee46
03-25-2006, 04:19 PM
Ah, dealer's already closed for now, wanted to check for 'ya... but check for audi/vw specialized shops around you... I see a lot of them around in PA.. search for them in Yellow pages, select 'name' not 'business category' I get any OEM parts I need from the shop I go to. Significantly cheaper than dealer prices.

Poopie
03-25-2006, 11:11 PM
Yeah, i know they are closed. I was hoping someone knew off the top of their head.

BarryT82
03-26-2006, 04:19 AM
My car uses the green one. I got it from ECS for about $5.00 and the dealer wanted $20. Now ECS is a little high on there shipping so it kind of evens out.

A4our
03-26-2006, 10:26 AM
I noticed I had the same problem yesterday, i.e. when cruising on the highway, it dropped one tick from the center. Do you guys think the problem is from the thermostat or the sensor? Where are these parts located? Thanks.

A4our
03-26-2006, 10:44 AM
I noticed I had the same problem yesterday, i.e. when cruising on the highway, it dropped one tick from the center. Do you guys think the problem is from the thermostat or the sensor? Where are these parts located? Thanks.

blacka4
03-27-2006, 07:09 PM
Does anyone have a picture of where the coolant temp sensor is on the 1.8T?

Poopie
03-27-2006, 07:19 PM
right between the engine and front firewall in the center. I just replaced mine, interesting story. I just picked one up from the dealer for $36 fom VW. Double what ECS wantes but after shipping its only $10 more and I know for sure it would work and didn't have to deal with anymore shit. Well when i removed my old one, I thought I dropped the old o-ring. So I didn't bother to check the hole for it and i just put in the new one and new sensor and I thought I locked it in. During my test drive after the coolant is all warmed up, I did a 3rd gear run and POP and smoke everywhere. I thought my engine was on fire. I immediatly pull over and check it out. My sensor popped off...I didn't know why. I checked the sensor and the o-ring is gone. I said damnnnn....so my friend picks me up to head back to my house to get some g12 and distilled water and to go get an o-ring. We go back and damnit, the same problem, the sensor won't seat right. I find that the orignal o-ring is still there. So yeah....that sucked. Anyways...this fixed a lot of problems. Start ups are great now, I pulled my plugs last week and they were fouled. Now I hope I'm not running so rich anymore. So far it looks good. I logged 100 miles today running around school and library to study and work and I'm slightly below the 1/4 tank mark. We'll see what happens. I think that my thermostat is still locked open? My temp will drop one tick when driving on a long straight and go back to the middle line when sitting at a long light.

check here for instructions and pics
http://www.audiworld.com/tech/eng47.shtml

A4our
03-28-2006, 01:56 AM
Poopie, your temp still drops by one tick when driving on freeway after you replaced the coolant sensor?

blacka4
03-28-2006, 04:58 AM
thanks..I need to get the sensor and the cam chain tensioner...damnit

Poopie
03-28-2006, 05:34 AM
yup, so i suspect its the thermostat now. Oh well, timing belt this summer.

mike-2ptzero
03-28-2006, 06:11 AM
Originally posted by blacka4
Does anyone have a picture of where the coolant temp sensor is on the 1.8T?


It is right in the bottom coolant hose right at the radiator, this is right above where the stock IC hose connects the IC tube that runs under the bumper and connects to the stock SMIC.

mike-2ptzero
03-28-2006, 06:16 AM
Originally posted by Poopie
yup, so i suspect its the thermostat now. Oh well, timing belt this summer.


If your thermostat is locked completely open your water temps will be much colder and so will your oil temps. The lower oil temps are a dead give away of a open thermostat.

Poopie
03-28-2006, 11:21 AM
both are colder when cruising. What are the affects of a engine running colder?

blacka4
03-28-2006, 12:33 PM
Not to hijack the thread but what is required oil pressure spec for an optimal engine. I have a feeling my oil pump is signing out

mike-2ptzero
03-28-2006, 12:33 PM
Originally posted by Poopie
both are colder when cruising. What are the affects of a engine running colder?


Running oil at low temps isn't that great for the motor. If the coolant is below 60 degs it will make the motor run in the rich/choke mode and might even run with less adv timing.

Poopie
03-28-2006, 12:49 PM
Damnit, I guess its got to wait a little longer to replace it with the timing belt in about a month.

A4our
04-05-2006, 06:19 PM
I replaced the thermostat last weekend and the coolant temp seems to be fine now. Thanks guys!

Poopie
04-05-2006, 06:21 PM
so your coolant temp stays right in the middle no matter what? Did you gas mileage go up at all?

A4our
04-06-2006, 12:49 AM
Yes, the coolant temp stays right in the middle once the car is warmed up [up].
I didn't notice the gas mileage go up though.