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2G Rad fan coming on late - SOLVED

frosh29

Proven Member
297
33
Jul 29, 2004
Wallington, New_Jersey
I have a 1995 talon tsi. Mostly stock besides a 16g.

Bought the car, ran new rear brake lines, fixed a massive oil leak in the flex turbo oil return, added a new coolant reservoir, and some other odds and ends.

Pretty suddenly the car started heating up at stops so I checked if the rad fan was working. Being a 2g, turning on the AC doesn’t tell you much about the radiator fans condition.

I pulled the coolant temp sensor plug out and both fans came on instantly. I bought a new coolant temp sensor (2 wire) and the same thing happens.

I let the temp get higher than I previously would with the car idling in my driveway and the rad fan kicked in at about 3/4 ways to the top of the temp gauge. It cools to halfway and the fan goes off. Ithe temp then goes to 3/4 the fan kicks on and goes back to half way. It repeats this pattern indefinitely.

Long story short the rad fan works, but it’s definitely kicking on at a higher temp than it should...

Any help would be appreciated.
 

Mham2k

Proven Member
258
40
Feb 8, 2008
Dallas, Texas
I have a 1995 talon tsi. Mostly stock besides a 16g.

Bought the car, ran new rear brake lines, fixed a massive oil leak in the flex turbo oil return, added a new coolant reservoir, and some other odds and ends.

Pretty suddenly the car started heating up at stops so I checked if the rad fan was working. Being a 2g, turning on the AC doesn’t tell you much about the radiator fans condition.

I pulled the coolant temp sensor plug out and both fans came on instantly. I bought a new coolant temp sensor (2 wire) and the same thing happens.

I let the temp get higher than I previously would with the car idling in my driveway and the rad fan kicked in at about 3/4 ways to the top of the temp gauge. It cools to halfway and the fan goes off. Ithe temp then goes to 3/4 the fan kicks on and goes back to half way. It repeats this pattern indefinitely.

Long story short the rad fan works, but it’s definitely kicking on at a higher temp than it should...

Any help would be appreciated.

The fans kick on at 210 degree's, which in my opinion is high anyway.

Do you have a way to measure the temp of the coolant?

Sounds like you need to flush your radiator or you have a leak somewhere, it shouldn't be getting that high.

After i figured out my cooling issues and was able to drive the car reasonably, I bought an aftermarket thermostat and now have my fans coming on at 170 in the Texas summer heat and 210 in the winter.
 

Mello

Proven Member
1,286
443
Jul 4, 2003
Albuquerque, New_Mexico
I would check the radiator cap. I found that only OEM seems to work proper. Not sure if you've replaced the thrmostat but it could be going bad. If you get a replacement make sure the little tickler valve is up at the 12 o'clock position. Also might want to rent a coolant pressure tester from a parts store & check for any leaks. Lastly make sure you burp all the air out so none is trapped. Normally the temp gauge should sit in the middle on the gauge cluster.
 

frosh29

Proven Member
297
33
Jul 29, 2004
Wallington, New_Jersey
I ran the car for about a month before this started happening. There are no coolant leaks besides what spilled out when I changed the coolant temp sensor. I topped off the coolant and burped the system last night and still had this issue. I also changed the radiator cap in the process, no change. After looking around I thought it may be low coolant also, but it was not the answer unfortunately.

I don't have a front mount intercooler, and besides, this is happening when the car is sitting still, not moving at all. Also the radiator wouldn't suddenly just develop a clog like that, out of the blue. I will attach a video so that you guys can see what I am talking about.

Am I right to think that the relays are fine since the fan DOES come on, just not at the correct time?

It leads me to believe that the coolant temp sensor I just purchased could have been defective out of the box. That or the thermostat may be going bad.

I will pick up a new thermostat tonight and replace it. I can go ahead and test the relays too, but I'm not sure that would help. If it would, someone let me know and I will test them for sure.

Thanks for the suggestions, I will update tonight.

-Scott
 

Jerzm3

Supporting VIP
255
39
Jan 18, 2015
mount holly, New_Jersey
Be weary of aftermarket temp sensors. I used an aftermarket temp sensor for the gauge cluster, and it showed my temps were higher than normal, when in fact they were normal when I checked them in DSMLink. Replaced with an OEM sensor, back to normal. I will only use OEM temp sensors because of that.
 

frosh29

Proven Member
297
33
Jul 29, 2004
Wallington, New_Jersey
210 is normal for fan kick on. If you had a tuning device, or logging device, you would see that the coolant temps hoover around 200 anyway.

I don't understand what you are trying to say here.

Be weary of aftermarket temp sensors. I used an aftermarket temp sensor for the gauge cluster, and it showed my temps were higher than normal, when in fact they were normal when I checked them in DSMLink. Replaced with an OEM sensor, back to normal. I will only use OEM temp sensors because of that.

The temp sensor that I changed is the 2 - wire sensor that tells the ECU what the coolant temp is. The single wire temp sensor that goes to the dash is OEM.

I am starting to think that I lost low speed on the Rad fan and that's what's going on. I don't believe I have another stock fan to test my theory though...

I'll mess around tonight and see what's up. Maybe install the Mishimoto.

I'll update this thread with more info when I get it. Thanks again.
 

rEclipserGST

Supporting Member
1,703
55
Nov 17, 2007
Columbus, Ohio
If you had a logger, you would see real time actual numbers. Not just a gauge as a reference. That gauge flarring up and down could and usually is only like 7 degree scale difference.

Buy a logger.
 

frosh29

Proven Member
297
33
Jul 29, 2004
Wallington, New_Jersey
There is no sense in buying a logger to find the coolant temp, thanks tho. I will be getting ECMLink shortly, so I'm not going to spend money on a logger for that one purpose. You've been super helpful though!

I will update the thread when I have more info in a little bit for anyone who is curious what the cause is.
 

luv2rallye

DSM Wiseman
7,970
841
Jun 7, 2003
Minneapolis, Minnesota
Understand on the stock 2g turbo there are 2 relays per fan (one for each fan winding). High speed is when both relays are on (both windings get voltage) so if one of your relays is bad, the fan won't go into high speed. Also if the 2 wire temp sensor is bad (or wrong resistance/temperature) the fan speeds are affected. The ECU controls ALL the stock fans relays. Here's some helpful info:
- https://www.dsmtuners.com/threads/bucking-for-a-couple-of-minutes-after-start.385461/#post-152374418
- https://www.dsmtuners.com/threads/r...onnect-the-temp-sensor.475221/#post-153390671
- https://www.dsmtuners.com/attachments/fan-operating-mode-2g-jpg.86862/
- https://www.dsmtuners.com/threads/cooling-issue-plus-wiring-them-up.273645/#post-151311484
- https://www.dsmtuners.com/threads/98-fan-relay-wiring.504508/#post-153596279

And a clever 2g manual fan override for severe overheating:
- https://www.dsmtuners.com/threads/cooling-issue-plus-wiring-them-up.273645/#post-151319397
 

frosh29

Proven Member
297
33
Jul 29, 2004
Wallington, New_Jersey
luv2rallye - Thanks for the reply. It seems to me that you are the resident wiring guy on 'tuners. I have been reading a bunch more of your write ups along my path to figuring this out. I will be saving the information that you provided for future reference. Also, I will need it when I start putting the next round of parts on this car, which is coming soon.

I did the following after my last post:

1. Tested each relay with a multi meter - All checked out good.
2. Tested the fuse for the radiator fan - Working.
2. Flushed the radiator.
3. Replaced the thermostat.

After all of that, the issue was still happening. I finally fixed it last night, and I have to apologize to rEclipserGST, as he (and others) led me in the correct direction. Although my temp gauge on the dash was moving around, my coolant was never boiling and the car was not overheating that I could tell. The only thing I had not yet changed was the dash temp sensor. I had one from my 1g, so I figured I would change it out and see what happened.

Once that was changed out with the one from my 1g, everything went back to normal.

So again, thank you all for the help! I def appreciate it!!
 
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