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98 Forester
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11 Posts
Discussion Starter · #1 ·
I recently moved to the High Desert in Ca from L.A. during summer temps can regularly be 100+ with possible highs of 115+. During a few 100+ my temps hit halfway.
I was wondering if there was any upgraded radiators possibly from an H6, or am I only able to get a Mishimoto or Cosworth lower temp thermostat? STI radiator cap?
Thanks in advance for any help?

Also the Forester was purchased from a family friend who works at a Subaru dealership and had the motor rebuilt within the last few years by the mechanic there. So there should be no issues with head gaskets or timing belt as it wasn’t driven very much.
 

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249 Posts
if this is an auto transmission car, then get a large/very large atf external cooler, and do the same for the engine oil; a large oil cooler,...mounted both in front area not in engine bay ........... easier faster, cheaper and more effective often than trying to fudge a deep row radiator into place, ......... keep the stock thermostat and radiator cap.these allow the system to get to proper heat and pressure range , the large oil cooler will help , use quality full synthetic oil only, 5w30 or 5w40 not 0w20 and filters made for that oil to allow faster.more full flow and higher oil pressure, a wix xp, napa platinum, puralator boss, or fram, ultra, dont use a standard media filter
 

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2017 Forester
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146 Posts
Phoenix here... tell me about the heat... I put a transmission cooler in mine - seems to run just fine.
 

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1999 Forester S
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530 Posts
Just make sure your car is in a good state of repair. Subaru tested the car in these conditions, you'll be fine as long as the thing has been maintained. Save your money for something else, like sunscreen and ice, lol...
 

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98 Forester
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11 Posts
Discussion Starter · #5 ·
Well I’ve been catching up on bills and maintenance lately. The FOZ seems to be doing a little better but still creeps halfway going up the hill from Ridgecrest toward Johannesburg on my way home on the 395. I’m planning on adding a trans cooler and running back into the radiator to keep the temp up during the winter, and hopefully help take some of the heat out of the radiator during summer. My next thought is changing the OEM oil cooler to this https://www.amazon.com/Subaru-21311AA071-Oil-Cooler/dp/B00IGZQCNK possibly if it fits and or is an actual upgrade, if not I’ll probably be looking to add an external oil cooler. I’m focused on making sure the SF5 will last before doing any upgrades.
I plan on doing a catback and some intake modifications so that I’m actually getting cooler air during the summer not from behind the headlight of a hot engine bay. Might look into the lightened crank pulley as well, as whatever HP I can free up will help.
 

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98 Forester
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11 Posts
Discussion Starter · #6 ·
So I thought I would update this thread. I added a transmission cooler and ran it from the hot line before the ATF hit the radiator (short line coming off the radiator). It definitely helped, but should have bought a bigger cooler, The Forester didn’t feel as heat soaked and struggling for power on those 100+ days, but it would still creep up halfway at times, but would cool down quicker.
The plus side for me is the weather is changing and cooling down, so running the cooler the way I did, I don’t have to worry about running the transmission too cold. I plan on buying a bigger cooler before next summer.
Hopefully this might help someone else if they have the same issues, which I saw posts on multiple forums but no answer, also buy the biggest cooler you can fit and some 3/8” line.
 
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