Welcome to the North American Subaru Impreza Owners Club Thursday July 10, 2014
Home Forums WikiNASIOC Products Store Modifications Upgrade Garage
NASIOC
Here you can view your subscribed threads, work with private messages and edit your profile and preferences Home Registration is free! Visit the NASIOC Store NASIOC Rules Search Find other members Frequently Asked Questions Calendar Archive NASIOC Upgrade Garage Logout
Go Back   NASIOC > NASIOC Technical > Normally Aspirated Powertrain

Welcome to NASIOC - The world's largest online community for Subaru enthusiasts!
Welcome to the NASIOC.com Subaru forum.

You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, free of charge, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, so please join our community today!

If you have any problems with the registration process or your account login, please contact us.
* Registered users of the site do not see these ads.
Reply
 
Thread Tools Display Modes
Old 01-04-2011, 08:07 PM   #1
davewilson
Scooby Newbie
 
Member#: 269045
Join Date: Jan 2011
Default 2.5 SOHC overheating, but only at highway speeds?

I did some searching and didn't come up with much, but I've got 2 friends with NA 2.5 impreza's and they are both showing the exact same symptoms at just over 100,000 kms. One is a 2004 Impreza 2.5TS, and the other is a 2005 Impreza 2.5i. Cruising around town, and anything up to around 90 km/h (about 55mph) they run at normal operating temperature, but anything over 90 km/h on the highway, or driving with a heavy foot around town they overheat! It has been a tricky one to troubleshoot, they have both replaced their thermostat's and they were fine, one has replaced his hoses in case the intake hose to the water pump was collapsing under high suction, and both have made sure there isn't anything blocking their radiators. There is no oil/coolant cross contamination but the only thing we can think now is maybe the head gasket is faulty and allowing combustion gases to be pushed into the cooling system when the engine is under heavy load?? Is there any history of this problem with this engine? I read that it was a problem with the older DOHC 2.5's, but can't find any history of this with the SOHC 2.5's. I was expecting to find a lot more about this on here since my 2 friends that have this engine both show the exact same symptoms! Weird!

Thanks in advance for any insight,
Dave.
* Registered users of the site do not see these ads.
davewilson is offline   Reply With Quote
Old 01-04-2011, 09:17 PM   #2
auslyle
Scooby Newbie
 
Member#: 129737
Join Date: Oct 2006
Chapter/Region: NWIC
Location: Bend Oregon
Vehicle:
04 Sweet Impreza
silver

Default

My 2004 Ts did this at about 100,000miles, replaced the Thermostat and flushed the radiator and it stopped doing it....
auslyle is offline   Reply With Quote
Old 01-04-2011, 09:29 PM   #3
JamesWilson2
ForumWars Winner!
 
Member#: 196948
Join Date: Dec 2008
Chapter/Region: TXIC
Location: Kyle, TX
Vehicle:
2003 Forester
Silver

Default

Stuck T-stat, bubble in the cooling system, or failing water pump? Missing plastic undertray?
JamesWilson2 is offline   Reply With Quote
Old 01-04-2011, 10:32 PM   #4
typhoonk
Scooby Newbie
 
Member#: 259497
Join Date: Sep 2010
Location: Bowmanville, Ontario, Canada
Vehicle:
1998 legacy L Wagon
Green/Grey

Default

check the radiator. May be clogged, and not getting the flow it needs when it works harder had higher speeds
typhoonk is offline   Reply With Quote
Old 01-05-2011, 10:08 AM   #5
Samirr76
Scooby Guru
 
Member#: 4835
Join Date: Mar 2001
Chapter/Region: Tri-State
Location: Fl33tw00d, PA
Vehicle:
2003 Baja 5MT
Yellow w/ 220,000 miles

Default

Sounds like a head gasket, except when mine went out, it was overheating at slower speeds, and was fine at highway speeds. You didn't mention how many miles are on your engine/vehicle...?
Samirr76 is offline   Reply With Quote
Old 02-01-2011, 11:35 PM   #6
davewilson
Scooby Newbie
 
Member#: 269045
Join Date: Jan 2011
Default

Thanks for the help and suggestions... one of my friends decided to take his car (2004 Impreza TS) into the subaru dealership to have everything checked out since the car is his wifes daily driver. So here is what they found, in case anyone does a search and finds this thread and wants to know the conclusion! They ended up doing the head gasket (and resurfacing), piston rings, two of the pistons (they had signs of piston slap) and they did the timing belt while they were putting it back together. A cylinder leak-down test is what found the head gasket leak. I just rigged up my own leak down tester and we're going to try it out on the 2.5i soon





... until then I've got to figure out why my 96 Legacy is only making 15psi fuel pressure :S I'm hoping it's just water frozen in the line, guess it doesn't like minus 30*C

Dave.
davewilson is offline   Reply With Quote
Old 02-02-2011, 10:38 AM   #7
Samirr76
Scooby Guru
 
Member#: 4835
Join Date: Mar 2001
Chapter/Region: Tri-State
Location: Fl33tw00d, PA
Vehicle:
2003 Baja 5MT
Yellow w/ 220,000 miles

Default

Sounds like a head gasket.
Samirr76 is offline   Reply With Quote
Old 02-02-2011, 10:57 AM   #8
Bluefoton
Scooby Specialist
 
Member#: 141373
Join Date: Feb 2007
Chapter/Region: E. Canada
Location: Quebec, QC
Vehicle:
2008 2.5i-hatch -
now with a HID retrofit

Default

Had same symptomps for HGs. Mind you (might be too late now though), I'd suggest replacing them with 11044AA642 (04-06 sti EJ255 gasket). Multilayered steel, better quality than the dealer-suggested replacement 11044AA633 (which isn't much different from the one that blows up)
Bluefoton is offline   Reply With Quote
Old 02-07-2011, 08:01 PM   #9
davewilson
Scooby Newbie
 
Member#: 269045
Join Date: Jan 2011
Default

Disregard the headgasket being the fix Wilbert took his TS out for a long drive on the weekend and once he got up to speed on the highway for a bit the temp climbed up to the red again, he dropped his speed back to 90km/h and it fell back to normal operating temp.

Now I'm thinking, the only thing that hasn't been changed between the two cars is the rad itself. The only thing I can think is that there might be a blockage in the rad that allows the coolant to flow enough at lower rpms but once the rpm hits a certain point the build up of pressure causes the water pump to cavitate, stopping the flow?? Thats my best guess right now, trying to track down someone with a known working rad that I can borrow for an afternoon.
davewilson is offline   Reply With Quote
Old 02-07-2011, 08:32 PM   #10
gmullin
Scooby Newbie
 
Member#: 271800
Join Date: Jan 2011
Default

the only way a water pump will cavitate is if you are at about 8500rpm,broken fins on the water pump or you have a blown head gasket nothing else will do that
gmullin is offline   Reply With Quote
Old 02-07-2011, 10:33 PM   #11
davewilson
Scooby Newbie
 
Member#: 269045
Join Date: Jan 2011
Default

Any idea what it could be then? Water pump is new, thermostat is new, hoses are new, head gasket is new (and heads were machined), rad is clean on the outside so nothing is blocking airflow, only thing left I would think would be some problem inside the the rad, or something to do with the heater core interfering, but I have a hard time seeing that.
davewilson is offline   Reply With Quote
Old 02-07-2011, 11:04 PM   #12
davewilson
Scooby Newbie
 
Member#: 269045
Join Date: Jan 2011
Default

I just downloaded a copy of the MY05 service manual and found a flow diagram of the cooling system, which shows that the coolant is free to bypass through the heater core any time the rad is blocked or the thermostat is closed, which like gmullin suggested, throws the possibility of cavitating out the window.



Also found this link though, which still makes me want to try swapping in a known working radiator:
http://www.tegger.com/hondafaq/overheating/index.html
davewilson is offline   Reply With Quote
Old 02-09-2011, 08:41 PM   #13
bmxpunk
Scooby Specialist
 
Member#: 89599
Join Date: Jun 2005
Chapter/Region: RMIC
Location: middle of nowhere, wyoming
Vehicle:
1995 almost 22B:)
red

Default

When I worked at the dealership, I had had a hand full of Foresters do this exact thing. The fix was replacing a plugged radiator. after drivng at highway speed, there was part of the radiator that you could touch and it felt cold (like warm coolant didn't go through it at all. It had all of the symptoms of a bad thermostat and headgaskets, but each time that wasn't the case.

I have my money on the "cooling system conditioner" causing the issue.

Unfortunately flushing the radiator didn't work, it was like concrete in there. Had to replace it on each occasion
bmxpunk is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
2.5 SOHC Engine Long Block, with only 72k miles danverco Engine/Power/Exhaust 3 10-03-2011 08:13 PM
2.5 SOHC block swap with 2.2 SOHC block DJBybee Normally Aspirated Powertrain 28 05-27-2011 11:59 PM
93 2.2 sohc heads on a 02 2.5 sohc, will they fit? Oldbluelegacy Normally Aspirated Powertrain 17 05-05-2010 01:22 AM
engine swap 2004 2.5 sohc to 2000 2.5 sohc rickinne General Community 4 06-08-2006 05:29 PM
grinding/vibrating above 2.5k in all gears and at highway speeds 83Rabbit Transmission (AT/MT) & Driveline 0 01-04-2006 11:53 PM


All times are GMT -4. The time now is 08:08 PM.


Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Powered by Searchlight © 2014 Axivo Inc.
Copyright ©1999 - 2014, North American Subaru Impreza Owners Club, Inc.