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Old 11-24-2008, 03:41 PM   #1
02RSBRP
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2013 WRX STi
Plasma Blue Pearl

Default Coolant tank overflow but car does not overheat (updated 12/7)

So I found coolant on the garage floor and started to think I may have a head gasket problem. I've search the forums, but haven't found any threads with the same symptoms as mine.

The car is a 02 RS, engine was just rebuilt 11,000 miles ago. Only thing that is no longer stock is the cams, I put some delta cams in while doing the rebuild. I followed the service manual when doing the head bolt torque. The car has never overheated on me or got above the middle of the Normal band.

So found some leakage and when looking under the car found coolant to be dripping from the thermostat housing bolts. The car had been sitting for about 3 days when I noticed the puddle and looked under the car. So I wiped the bolts and the entire area clean. Started the car and watched that area, no leaks. So started looking elsewhere on the car, but found no leaks. The overflow tank was at the LOW mark on the tank. While the car was still below the NORMAL temp mark, I brought the RPM's up to about 3k, and I started to see bubbles in the overflow tank. The overflow tank level also started to go up. I continue to let the car warm up. Once the car was warm, I did a combustion gas check on the coolant, it showed NO signs of combustion gases. The car never got any warmer than normal. The overflow tank got up to the full mark, but it mostly filled when I took the cap off to do the combustion gas test.

I took the car for a drive and ran it hard keeping the RPM's between 3k and 5k. I accelerated hard when starting. The car temperature stayed near the lower part of the NORMAL band the whole time. When I got home, tank level was still the same as when I left for my drive.

I don't think this is a Head Gasket problem, but need some help in trying to figure out what is going on. I'm thinking that when the car is cold, I do get a little leakage, but once warmed up, everything seals up and is good.
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Last edited by 02RSBRP; 12-07-2008 at 10:14 PM.
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Old 11-24-2008, 04:13 PM   #2
Tim Sanderson
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00 Impreza 2.5 RS
Blue Ridge Pearl

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So is the overflow overflowing? There should be some fluid in there to compensate for thermal expansion and evaporation.

The overflow level should go up a little when the motor is warm/hot and it should fall back down after it cools.

Check your radiator hoses with the motor cold. Are they collapsed at all?
Yes-replace radiator cap.

I would double check all your hose clamps and t-stat housing bolts. Does yours have the plastic t-stat housing?
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Old 11-24-2008, 04:19 PM   #3
02RSBRP
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It overflowed at some point, that is what put the puddle on the ground under the car.

The radiator cap was just replaced 9000 miles ago. One of the things I forgot about during the rebuild, but then remembered it and got it on.

I'll check the radiator hoses. Those are both new, put in when I rebuilt the engine 11k miles ago.

Checked all the hose clamps already. Yes I do have the plastic t-stat housing. I checked that good and didn't see any cracks or anything on it.

How much of a rise should you see in the overflow tank?

What about there being a Head Gasket leak when the car is cold, but seals itself once the engine warms up?
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Old 11-24-2008, 09:04 PM   #4
rhino6303
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I had a problem similar to this once. Like said above, I would check the radiator cap again; that was my problem. Easy way to check the cap is to boil it in a pot with a thermometer in the water and see when the cap opens up. However, I don't remember what the temperature should be when the cap opens up. I hope you get it figured out.
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Old 12-07-2008, 09:14 PM   #5
02RSBRP
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So after looking at everything it didn't look like anything was leaking. So that is why I assumed that the overflow had overflowed. I drove my car to a from work (total 100miles) for an entire 7 days and never saw any leaks. I also never saw the overflow tank get any higher than 1/2 when car was at normal temperature. When the car cooled down and I would check it before leaving for work, it was always at the same spot.

So my last day for the week was Thursday. So I parked my car Thursday night. Everything seemed normal. I checked and saw no leaks on Friday afternoon. Saturday morning, I notice a small puddle under the car. I look and can see coolant on one of the thermostat housing bolts and the thermostat housing has some on it.

Tim, I do have the plastic t-stat housing and I checked my radiator hoses when the car was cold, they do not collapse. Both hoses, t-stat, water pump, and clamps where replaced with rebuild.

Starting to think that the o-ring for the t-stat housing is leaking or a problem with the t-stat housing itself.
Any other thoughts on this?
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Old 12-07-2008, 10:26 PM   #6
ballitch
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Buy a metal T-stat housing. Still dont know why subaru decided plastic is better. It's almost weird how the metal rear oil seperater plates and metal T-stat housings disappeared.....I guess it's cheaper, and when you make 50,000 cars, $3 a car is alot of money.

I just went to the junkyard and bought a couple alum. T-stat housings.

Getting a little cold in Idaho this time of year, for junkyard runs at least.


~Josh~
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Old 12-08-2008, 04:17 PM   #7
02RSBRP
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That's what I was thinking about doing. Anybody know where I can purchase a metal t-stat housing?
I've looked and haven't come across any. I don't think the WRX t-stat housing will work because it comes off the front of water pump where ours comes off the bottom.
I've looked, and in this area there are no junk yards that even have subaru's. I think I've seen a total of maybe 12 other subaru's in this area.
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Old 12-08-2008, 04:39 PM   #8
Mavrik
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If your coolant overflow is overflowing, then likely you have an internal headgasket leak. compression from the cylinders force their way through the coolant passage causing coolant to be pushed out of the block.
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Old 12-08-2008, 04:55 PM   #9
02RSBRP
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It's not the overflow that was causing the puddle. Read my post that I wrote yesterday. After looking at it several times, appears to be the the plastic t-stat housing causing a leak, and if it leaks, probaly lets some air get sucked into waterpump which is what caused my couple of air bubbles when reved high.
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Old 12-08-2008, 09:56 PM   #10
t3t4meat
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change the o-ring seal that goes around the thermostat itself, that is the gasket which is probally leaking. you shouldn't need a new thermostat housing unless its cracked or warped which is unlikely, but a new plastic one should be fine.
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Old 12-09-2008, 04:48 PM   #11
ekuna
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My Legacy was towed to the dealer last night. I was careful not too drive it. The service person talked to the regional Subaru rep. If it is a head gasket, they will fix it under the extended warranty. This is my first major repair at a dealer in 20+ years and 42 vehicles. I am curious how C&S Subaru will treat me.
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