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Coolant temp flucuation.

3K views 22 replies 7 participants last post by  XJman 
#1 ·
So today I was sitting in traffic and noticed my temperature gauge was a needle width above the middle hash. After I got moving after a minute it dropped below the middle hash about a needle and a half, and after about 5 minutes of normal driving fell back on the middle hash and hung there until traffic stopped for about 10 minutes again. This may be normal, however I've never owned a vehicle that would have a noticeable change on the gauge when idling. I called my local dealer and they just told me to bring it in, they can't tell if its normal over the phone. I'm not paying them 100 bucks an hour to tell me my car is fine.

I've checked the tank and it shows between low and full when warm, I don't see any noticeable leak, however I've not pulled the bottom plastic off of it to look closer yet, I wanted to avoid that if this is normal. The only thing that I did notice when I got home I parked in my drive way and let it idle for a minute and wait for the fans to come on, they came on but only ran for about 15 seconds before turning off for about another 15, then back on. I didn't have any ventilation on, and my windows were down, at no point did anything smell hot. I read elsewhere it could be a thermostat, or some freeze/bypass plug in the water pump but I would think I would have a much larger temperature variation if either were bad.

I'm not really against changing the pump and thermostat because I had planned on doing the timing belt, waterpump and pulleys this summer because I'm paranoid about a timing belt failure.
 
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#2 ·
The simple answer is that cars run colder when they're moving due to the increase of airflow across the radiator/engine. When you're sitting in traffic the only thing cooling your car is the water pump and the fans.

Where are you located and what year car?
 
#3 ·
I'm in the Cinci area, and its a 2011 with 70k.

I understand that when I'm moving it will by nature cool everything more. I've just never noticed a temperature gauge on any vehicle move a discernible amount.
 
#6 ·
Just an update and a bump for anyone with any other info.

It doesn't seem I have any air in the system, I verified there is no coolant leaks. I guess I'll have to have the coolant checked to see if its a head gasket.
 
#7 ·
You might be able to borrow or rent a pressure tester with the correct fitting for your rad cap, and pressure test the system. I'd not suspect a head gasket out of nowhere, as there are so many other things that are more common (and cheaper). How old is your car?
 
#12 ·
Well, I thought I'd update this after I burped the radiator again after a buddy told me I didn't do it long enough, and my ghetto funnel and a plug was too ghetto so he let me use his junk.

Its been a few days and various weather from about 65 down to 30. The temperature is much more stable, however it still drops more than I would expect at cruising speed 60-70mph. The needle never goes past mid line, and at 65 the needle will drop but not enough to completely show the line.

So thanks for the comments folks.
 
#14 ·
I was just burping at the radiator. I had all the heat on, I'm going to burp it again when I get a chance. Its spring cleaning and I have a yard of trees and a bunch of bush I cut this winter I've got to take care of so I won't be messing with it until later this week or next weekend
 
#19 ·
The splash shield? The one you need to remove for...well everything lol?

You'll probably be spending a lot more for a piece of plastic than what you'll probably want to.

I'm debating ripping mine off for the same reason
 
#20 ·
Yeah that thing. I was under there looking for leaks and took it off so I could actually see, got lazy and didn't put it back.

I figured it was expensive, I'll check some places and see if I can find an aluminum one or something actually functional and with holes to get to things.
 
#22 ·
When I worked for toyota, part of the splash shield on the prius needs to be pulled away to get to the filter and plug. It's designed to fold where the plug and filter is, except after a few times it breaks off. Customers who wanted quotes were surprised the thing was about 200 bucks
 
#23 ·
Yeah my BMW had a cut out for oil and filter and so did my vw if I remember correctly. Awesomely my 2012 wrangler the filter was on top of the motor so it drained into the block. Genius design.

I'm looking now. I found an aluminum one for about 260 with holes for fluids, but I'll update here as I go.
 
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