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Old 01-29-2017, 10:37 PM   #1
T_Sibary
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Default Overheating, new thermostat, no coolant leaks, no coolant in oil. HELP

I'm new to the Subaru world and nasioc. I have searched and searched asked friend and friends of friends that own subarus and I keep getting different options "bad thermostat", "water pump","head gaskets" . I recently bought a 04 wrx wagon 5 speed. Car has 135k miles and only mods are aftermarket turbo Inlet tube, up pipe and radiator hoses.

Recently on my way to work it's started to try and get hot. I'll start the car 5-10 min before work and about 5-10 min of driving the temp hand will start to rise past normal. Then if I coast it will go to normal and won't do it again.

Well the other day I was leaving work and it did fine. That next morning it did it again but this time started to get hotter and when I tried to coast it would cool down. (Note every time this has happens I have had the heater on due to cold weather)

Well while I'm leaving work that day the temp hand started to rise. I'd coast it would cool off and be fine. But this time I noticed when the temp hand started to rise. I'd loose heat but once it got back to normal I had have heat. Like the thermostat opened up. I figured that's what the issues was, a sticking thermostat. So I changed the thermostat and it was fine after driving it that evening.

Here it is Sunday. I started the car up to let it warm up. 10min later after letting the car warm up. Me the wife and baby leave to go to town. After about 5 or so min I stop and get gas and notice the temp hand started to rise. So I **** it off, pump my gas and after that it hasnt tried to overheat all day, even after sitting 2 hours then leaving for town again it never tried to get hot. I've noticed that the heads on the car have been painted. Which makes me believe that the head gaskets have been replaced once and that I'm hoping they did a timing belt and water pump.

The car has new thermostat, and when I installed it I let it run for about 30 min with heat on using a coolant funnel.

Please help it's driving me crazy.
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Old 01-29-2017, 10:55 PM   #2
mrsaturn7085
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Are you pinning the needle? If not, you aren't overheating, you're just doing the right thing and paying attention to some strange gauge behavior.

Do you have the ability to read the actual coolant temperature through the OBD port using an AP or otherwise? If so, what peak temp. are you seeing?

My gut feeling at this point is that you have a fan issue. If you had a HG failure, you'd overheat due to coolant loss and the issue wouldn't fix itself. You've eliminated the thermostat as a potential issue, so the next possibility after fans is the radiator cap.

Best of luck in finding the issue - the good news is that it really doesn't sound like a HG failure.
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Old 01-29-2017, 11:17 PM   #3
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Quote:
Originally Posted by mrsaturn7085 View Post
Are you pinning the needle? If not, you aren't overheating, you're just doing the right thing and paying attention to some strange gauge behavior.

Do you have the ability to read the actual coolant temperature through the OBD port using an AP or otherwise? If so, what peak temp. are you seeing?

My gut feeling at this point is that you have a fan issue. If you had a HG failure, you'd overheat due to coolant loss and the issue wouldn't fix itself. You've eliminated the thermostat as a potential issue, so the next possibility after fans is the radiator cap.

Best of luck in finding the issue - the good news is that it really doesn't sound like a HG failure.

No I'm not pinning the needle. It just goes up the the line above the middle of the temp gauge. I can see if I can barrow a buddy's Snap On scanner to watch the temp through it. I didn't mention it but yes the cooling fans are working. But I've notice they run none stop. Do they have stages of speeds. Like medium and high. Or just one speed. Also could a radiator cap really give these symptoms?
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Old 01-29-2017, 11:33 PM   #4
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Sounds like a air pocket that hasn't managed to work its way out.
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Old 01-30-2017, 08:13 AM   #5
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Also the car has some sort of cheap jdm radiator cap HKT is the brand it's on the resivour by the turbo. Wonder if that could be letting air into the system.

Last edited by T_Sibary; 01-30-2017 at 09:14 AM.
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Old 01-30-2017, 10:40 AM   #6
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I assume you have two radiator caps, one on the coolant expansion tank on top of the engine, and one on the radiator.

The cap on the radiator needs to be rated to a higher psi than the cap on the coolant expansion tank.

The factory cap on the expansion tank is rated at 108kPa (15.6psi) the factory cap on the radiator is 137kPa (19.8psi). If both caps are the same rating, you will continue to get air coming into the system.

Also make sure the overflow hose coming from the top expansion tank is connected with a Y adapter piece (8mm), so both overflows connect to the hose which runs into the coolant overflow tank on the side of your radiator.

Make sure the overflow hoses are in good shape, and are 'air tight' when your engine cools down, the engine needs to draw coolant back into the system, if your overflow hose has a crack in it, the system will draw air in rather than coolant.

Lastly, I your temp gauge should sit a little below half way. The coolant temp gauge on your dash does a terrible job, but this is by design. The gauge is 'weighted' so that it will sit just below half way, through a wide range of temperatures.

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Old 01-30-2017, 11:47 AM   #7
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Quote:
Originally Posted by rexxxy View Post
I assume you have two radiator caps, one on the coolant expansion tank on top of the engine, and one on the radiator.

The cap on the radiator needs to be rated to a higher psi than the cap on the coolant expansion tank.

The factory cap on the expansion tank is rated at 108kPa (15.6psi) the factory cap on the radiator is 137kPa (19.8psi). If both caps are the same rating, you will continue to get air coming into the system.

Also make sure the overflow hose coming from the top expansion tank is connected with a Y adapter piece (8mm), so both overflows connect to the hose which runs into the coolant overflow tank on the side of your radiator.

Make sure the overflow hoses are in good shape, and are 'air tight' when your engine cools down, the engine needs to draw coolant back into the system, if your overflow hose has a crack in it, the system will draw air in rather than coolant.

Lastly, I your temp gauge should sit a little below half way. The coolant temp gauge on your dash does a terrible job, but this is by design. The gauge is 'weighted' so that it will sit just below half way, through a wide range of temperatures.


This is the cap on the radiator



This is the cap on the expansion tank



I check all the hoses going to and from the radiator and expansion tans and they all appear to be in good condition. I'm wondering if the cap on the expansion tank is causing me all the problems. Since it's some aftermarket brand that I cannot find anything about. Also my temp hand sits a little more in the middle then the one shown. But when it try's to run hot it will go to that line above the needle.
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Old 01-30-2017, 01:40 PM   #8
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Replace the aftermarket radiator cap with a new OEM part - it's not a guarantee, but yes, the cap CAN cause this problem; I have personally had it happen before and was shocked when a new cap fixed everything. It's a cheap way to eliminate one variable.

If your needle does not continue to rise beyond the 3/4 mark, you are NOT overheating. Continue to monitor and diagnose after cap replacement, but don't panic.
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Old 01-30-2017, 03:21 PM   #9
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Quote:
Originally Posted by mrsaturn7085 View Post
Replace the aftermarket radiator cap with a new OEM part - it's not a guarantee, but yes, the cap CAN cause this problem; I have personally had it happen before and was shocked when a new cap fixed everything. It's a cheap way to eliminate one variable.

If your needle does not continue to rise beyond the 3/4 mark, you are NOT overheating. Continue to monitor and diagnose after cap replacement, but don't panic.
Ok thank you. Reason I'm so worried is because I just bought the car lol. ***129310;***127996; A new cap will fix it.
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Old 01-30-2017, 04:12 PM   #10
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Hoping so! Report back!
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Old 02-01-2017, 04:50 PM   #11
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After letting my car run for 45 min with the expansion tank cap off. So far so good. Thanks for the input and help.
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Old 02-01-2017, 10:35 PM   #12
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I think you might just be seeing the thermostat open and close.
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Old 02-02-2017, 07:49 AM   #13
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Default Overheating, new thermostat, no coolant leaks, no coolant in oil. HELP

137 kpa goes on the reso by the turbo, 108 kpa goes on the rad

an easy i use to remember is the lower pressure has to go on the lower point of the car.

if you look eye level... the rad cap is a few inches lower.
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Old 02-02-2017, 11:00 AM   #14
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Quote:
Originally Posted by Titter View Post
137 kpa goes on the reso by the turbo, 108 kpa goes on the rad

an easy i use to remember is the lower pressure has to go on the lower point of the car.

if you look eye level... the rad cap is a few inches lower.
I think you have that backwards.
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Old 02-02-2017, 12:03 PM   #15
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that's how mine is, that's how mishimoto says to do it in their instuctions with their new radiators, and that's how my builder told me set it up. been well over a year... works fine. had it like this on an oem rad, a mishimoto oem replacement rad, and a mishimoto alum rad... all worked fine.

could i be wrong? maybe... but the supporting evidence seems to suggest otherwise.

Last edited by Titter; 02-02-2017 at 12:10 PM.
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Old 02-02-2017, 01:39 PM   #16
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Quote:
Originally Posted by Titter View Post
that's how mine is, that's how mishimoto says to do it in their instuctions with their new radiators, and that's how my builder told me set it up. been well over a year... works fine. had it like this on an oem rad, a mishimoto oem replacement rad, and a mishimoto alum rad... all worked fine.

could i be wrong? maybe... but the supporting evidence seems to suggest otherwise.
You have it backwards:

The high pressure (137 kPa) [relief valve] cap is the radiator.

The upper tank [radiator] cap can be either the OEM lower value (108 kPa) or an up-rated cap (137 kPa = STI option part).

From the FSM:

Quote:
If the relief valve cap is fit on the coolant filler tank, overheating may occur.
The wording is slightly confusing as the 'radiator' cap is not on the radiator. The round cap is the 'relief valve' cap.
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Old 02-02-2017, 02:23 PM   #17
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well backwards seems to work just fine. the mishimoto rad cap is of different construction, but i still use a lower pressure cap on the lower rad cap and i've never overheated.

Last edited by Titter; 02-02-2017 at 02:36 PM.
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Old 02-02-2017, 02:56 PM   #18
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Titter - consider this, who do you trust more in terms of the engineering of the cooling system: Mishimoto or Fuji Heavy Industries?

Side-note - all install videos for Mishimoto radiators on Subaru cars show the 1.3 bar cap installed on the radiator, which matches the OEM method. The marketing materials claim "Included 1.3 bar radiator cap raises the boiling point of engine coolant to provide a safer and more efficient system" which is false - the OEM 'relief valve' cap is 137 kPa while the Mishimoto cap is 1.3 bar (130 kPa). Not only does this NOT raise the boiling point... it actually reduces it.

The self-bleeding aspect of the cooling system will be compromised by placing a lower pressure cap at a point below the highest point in the system. This can allow air into the system which can cause overheating. Just because you haven't overheated doesn't mean your method is better than the OEM method - it is very obviously inferior in terms of how a cooling system is designed to self-bleed.

The only reason the upper tank is even required is to accommodate the turbocharger and throttle raising the coolant level above the 'relief valve' cap (which is the 'radiator' cap on non-turbo models).

To further understand why the higher pressure cap needs to be on the lower radiator, you need to consider the cool-down phase. When coolant is returning from the reservoir tank, the OEM method pulls the coolant into the upper tank, which is then allowed to bypass the thermostat and flow directly through the water pump.

Now here's the rub - when you swap the caps, the coolant will now be drawn into the radiator 'relief valve' port, which is now capped by the lower pressure 'radiator' cap. If the thermostat is closed, you will still have the pump pulling coolant through the upper tank, however the path to the overflow is likely closed due to the higher pressure cap installed on the upper tank. A quick review of the system schematic shows that the upper tank receives coolant IN from the turbocharger and (normally) the overflow, and coolant OUT to the top of the radiator, the overflow, and the water pump (again, bypassing the thermostat). Coolant is still being pumped away from the upper tank, through the turbo, and back into the tank so what do you think happens to the small line running to the top of the radiator (which normally moves coolant AWAY from the upper tank)? Flow is reversed and any air in the radiator itself will be transferred to the upper tank. Since the upper tank valve is a higher pressure than the radiator, this air is never purged.

Last edited by mrsaturn7085; 02-02-2017 at 03:11 PM.
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Old 02-02-2017, 03:40 PM   #19
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turns out the mishimoto cap is a 2 way relief valve. so i guess nothing i said is valid.

Quote:
Caution

The provided Mishimoto radiator cap should replace the stock cap located on the expansion tank. The stock cap attached to the radiator should be installed on the Mishimoto Performance Aluminum Radiator. The Mishimoto radiator cap is a two way valve, while the stock radiator cap is a single valve. Due to the difference in construction, the Mishimoto cap cannot be used on the radiator. If the Mishimoto cap is fit on the radiator, overheating may occur.
(this is copied from mishimoto https://www.mishimoto.com/subaru-wrx...diator-01.html)

Last edited by Titter; 02-02-2017 at 03:59 PM.
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Old 02-02-2017, 04:08 PM   #20
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All radiator caps are two-way relief valves - that is how they purge excess pressure then refill from the expansion tank during the cool-down cycle. Mishimoto is correct - the 'relief valve' cap is not a 'radiator' cap.

The fact they show the Mishimoto valve installed on the radiator in the install video yet tell you not to do this on the product page is a nice touch... I bet the radiator ships with the valve installed on the radiator, too. Sure seems like it would make more sense to keep them separated and place a giant sticker over the radiator port saying "STOP: REUSE OEM RELIEF VALVE" or something similar.

The good news (I guess) is that by placing the 1.3 bar cap on the upper tank, they're not lying about the system pressure going up. An increased coolant system pressure is not a decision that should be made on a whim... will it raise boiling point? Yes. Can you do the same thing by altering your coolant mix? Usually. Only one of these two options increases the risk of failure/leakage of a critical system.

Last edited by mrsaturn7085; 02-02-2017 at 04:17 PM.
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Old 02-03-2017, 08:02 AM   #21
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you're bang on. the cap is also on the rad in the pictures on-line as well as on the rad when it comes in the box. i agree it is very, very, misleading.

but none-the-less. the intructions say to do so, my builder (who i trust above mishimoto and FHI) told me to do so... and its been working well over a year/30,000km.
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Old 02-05-2017, 12:36 AM   #22
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I use the round 137KPA OEM cap on my radiator itself and the 108KPA OEM cap (with the wings) on my upper tank. I believe this is the proper way.

Also, monitor your overflow reservoir/coolant overflow tank, monitor the level of the coolant. if it starts to bubble and spraying coolant all over like mine before:

https://i.imgur.com/BFBeRTK.jpg

Youre gonna have a bad time....
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Old 02-06-2017, 12:30 PM   #23
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Hi there, I too am new to the world of Subie and Boost.

Maybe this will help you... I picked up the car 2 days ago and realized it was overheating. I parked it, checked the coolant and it magically was gone. Refilled it and drove again... same thing. Goes faster when I drive hard.
Yesterday I went over all the clamps, hoses etc and found allot were not as tight as they should be, and I added an addition clamp to the line running to the turbo (I couldn't reach the existing one). After doing this I was able to drive it nonstop almost 500 miles, from Lackland florida to kennesaw, georgia.... she's fine now

Check yours. Also make sure your coolant cap is good and tie not running to much water.... water will evaporate.
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Old 12-31-2020, 05:52 PM   #24
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Default Similar issue on 04 Wagners 210k

I have been having an overheating issue for about a year that has been getting increasingly worse.

Mine is a slightly different issue. My car used to overheat only in fifth gear and only when going up a grade. Such as up a mountain hill for skiing or over the passes. Then it began happening in fourth as well.

The issue expanded to the highway. At highway speeds (interstate included) the same overheating issue occurs.

Recently, I have been overheating even just at idle or when driving around town regardless of speed.

Here's where it gets weird. The only way I was previously able to get my needle to drop and cool the engine down was to absolutely floor it. Ramp up my rpms above 4500 and then needle drops like a rock. This method is still helpful to an extent, but not for as long -- it almost immediately begins to rise again these days. Because of this, I thought perhaps I had an issue with the thermostat or maybe the valve due secondary to a failure to build enough pressure to open the valve and allow the coolant to flush.

I would also like to add that the car is absolutely overheating not just showing on the gauge. It is not an issue with the needle or thermostat as the car smells like its melting internally if I can't cool it down and keep it cool.

I have been to three different shops. I have done research and absolutely have not been able to solve or correct this issue. I am concerned at this point that my heads are warped (or getting there) and I may be at risk of throwing a rod.

Not sure if any of this is helpful, but thought id share just for another outlook and experience to consider.
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Old 01-04-2021, 11:10 AM   #25
K3rm1tth3fr0g
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Quote:
Originally Posted by _sauce View Post
I have been having an overheating issue for about a year that has been getting increasingly worse.

Mine is a slightly different issue. My car used to overheat only in fifth gear and only when going up a grade. Such as up a mountain hill for skiing or over the passes. Then it began happening in fourth as well.

The issue expanded to the highway. At highway speeds (interstate included) the same overheating issue occurs.

Recently, I have been overheating even just at idle or when driving around town regardless of speed.

Here's where it gets weird. The only way I was previously able to get my needle to drop and cool the engine down was to absolutely floor it. Ramp up my rpms above 4500 and then needle drops like a rock. This method is still helpful to an extent, but not for as long -- it almost immediately begins to rise again these days. Because of this, I thought perhaps I had an issue with the thermostat or maybe the valve due secondary to a failure to build enough pressure to open the valve and allow the coolant to flush.

I would also like to add that the car is absolutely overheating not just showing on the gauge. It is not an issue with the needle or thermostat as the car smells like its melting internally if I can't cool it down and keep it cool.

I have been to three different shops. I have done research and absolutely have not been able to solve or correct this issue. I am concerned at this point that my heads are warped (or getting there) and I may be at risk of throwing a rod.

Not sure if any of this is helpful, but thought id share just for another outlook and experience to consider.
Holy **** that sucks!

Have you replaced thermostat, water pump, radiator and all other semi wear components?

If not it's time.
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