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View Full Version : Normal operating temp while driving. Overheating when started again



sirsmokealot303
07-31-2014, 12:19 AM
1998 a4 AEB 1.8t 5spd 163,000

I have got more compliments about my car during the last week than i have the 2.5 years that i had it... and just yesterday i noticed that the temp stays right at halfway when driving, but when i shut it off and let it sit for a few minutes then restart it the gauge reads a little high... almost 3/4 of the way. The temp slowly drops back down to the 1/2 mark in less than a minute. It happened to me multiple times yesterday. But as soon as i pulled out the camera the problem decided to go away (as usual). I replaced water pump and thermostat less than 10k ago when i did the timing belt (ecs tuning ultimate kit) roughly 1 year ago. I replaced my heater core hose a few months later, and again bled the air out of my heater hose over this last winter. I'm not loosing any coolant, It is still at the same level. Just curious if anybody else has experienced anything like this or has any ideas... I know on other vehicles i was getting bad thermostats that only lasted a year, if that long... I plan on bleeding the air out again (starting with the easiest and cheapest possible solution) And hopefully get some opinions before doing anything else. Thanks for any help in advance.... Oh yeah, The weather here has been in the 70's with lots and lots of rain. So its not like its 100* or anything

P.S. Not sure if this is related but When i bled the heater hose i got a decent amount of air out of it, but my heater still doesn't blow hot... only medium warm... on really cold days below 0* it blows ice cold... The temp gauge always read normal. The car had a brand new $2000 heater core receipt when i purchased the car and now its currently about 20k miles later

fR3ZNO
07-31-2014, 05:24 AM
So if I understand this, the coolant temp goes up after turning off the car and starting a few minutes later?

This is completely normal. Especially if you drove the car hard and shut it off immediately. With the car off, the coolant has nowhere to flow, so it just sits. The temp sensor is near the cylinder head, where a lot of heat will be concentrated, so the coolant in the cylinder head gets heated up and causes the reading to go up.

Not sure if the AEB has it, but I know that my ATQ a̶n̶d̶ ̶A̶W̶M̶ have small electric coolant pumps that circulate coolant after the car has been shut off in order to combat your issue. Even with the coolant pump, I notice that the gauge does creep past the halfway mark if I go to start it a few minutes later.

walky_talky20
07-31-2014, 05:32 AM
AWM have small electric coolant pumps

Pics or it didn't happen.

fR3ZNO
07-31-2014, 05:38 AM
Pics or it didn't happen.

I guess I was mistaken, my apologies. So, the V6's (2.8, 2.7T) only have the after run pump?

walky_talky20
07-31-2014, 06:05 AM
I was just teasing you. Yeah, just the V6. Also the VR6 in the Jetta's (if you swing that way). And the W8 Passat.

Some inventive persons have added the pumps to the heater core path to help flow through the core. I was kind of hoping you'd post a pic of homebrew setup of a previous owner that was so good it looked stock.

jacobaudi
07-31-2014, 12:00 PM
My 2.8 does that also and also my buddy's 2.8 lol it's weird but normal

demonmk2
07-31-2014, 12:02 PM
Not sure if the AEB has it, but I know that my ATQ a̶n̶d̶ ̶A̶W̶M̶ have small electric coolant pumps that circulate coolant after the car has been shut off in order to combat your issue. Even with the coolant pump, I notice that the gauge does creep past the halfway mark if I go to start it a few minutes later.

For reference, AEB's do not.

sirsmokealot303
07-31-2014, 02:53 PM
@Walky_Talky... this isn't normal is it? I have had the car for over 2 years. Very attentive to my gauges and have never noticed this until the other day. It was probably after a 2 hour drive in cold rainy weather. I never drive the car hard because i know its not fast (stock @150bhp) infact its probably the slowest car i have ever had, so i baby it

BaseDrifter
07-31-2014, 04:29 PM
I'm not walky, but it is normal. So long as the car returns to normal temperature within a few minutes of starting then you're fine.

It's physics, baby. Gauge reads sensor, sensor sits in coolant, stagnant coolant absorbs extra heat from the motor once shutdown, temp goes up.

With the car on that coolant gets circulated and cooled with the help of the pump and fan.