Overheating after head gaskets

[RoughDiamond]

Well, I'm at wit's end. I'm normally not stumped by these problems, but I don't want to start shotgunning parts.

91 Lego SS, 4EAT, 191K miles, just did Subaru 282 headgaskets, head and block checked-out good, flushed the block, heater core and coolant tubes. Radiator is newer and SEEMED to flow well (water out was just as fast as water in). New Water pump (old was original and seized) and thermostat and OE radiator cap.

Car was running well for a few days, no coolant leaks nor even a hair above normal op temp. Now, on longer extended runs on the highway (under 3K RPMS), it will start to climb. However, if I spank it, never moves on the temp gauge. Both cooling fans kick on around op temp and will stay on, full blast.

Upper hose is hot, pass side radiator tank gets hot, but lower hose and the rest of the radiator is ice cold. If I rev the motor past 3K for a few seconds, the lower hose starts to heat-up and the temp across the radiator starts to equalize. But the fans never come off. The coolant in the bottle stays steady until the car REALLY heats up, then the lever rises a bit, but NO bubbles, no funny smelling coolant and the level returns back to the previous level once it cools down. No coolant missing. If I squeeze the upper or lower hose, I can hear the check ball in the expansion tank and the jiggle valve in the thermostat moving so I know they both have coolant and it's somewhat moving.

I BELIEVE I put an OEM thermostat in there, but I can't be 100% sure ATM. I had the new one by the Stant XACTSTAT (and yeah, the exact stat is VERY similar), sitting on the bench, I purchased an OEM (knowing how picky they are) but can't confirm if that's what actually went in to the car (the previously used thermostat has since gone back to the parts store, assumed it was the Stant).

NOW, does this sound like a thermostat issue, a radiator issue, a water pump issue (not enough flow to circulate the hot water by the thermostat) or another head-gasket issue. I feel it's a thermostat issue, but the RPM dependency has me questioning the water pump or flow of the radiator.

Ideas?

[Legacy777]

It sounds like a thermostat to me. I would get a new Subaru thermostat and try that.

[RoughDiamond]

Well, after approx 60 miles with varied driving (even though it was in single digits today), the problem seems to have been solved.

I pulled the radiator and drained the coolant (new lower hose going on, and to check the thermostat). Coolant was clean, thermostat was the new Subaru one and double checked it opened @ ~175F (nearly boiling water, confirmed with thermometer).

For fun, I decided to check and see if any junk would come out of the radiator. OH. MY. GOD. It's like a snow globe had exploded in my radiator. Back flushed it with hot water and out came CHUNKS of the old stop-leak the PO had put in before he sold it to stop the hose leak. MUCH like the crap I flushed from the block, heads, heater core and hoses... Let concentrate flush sit with hot water in the radiator for approx 10 mins and after several more rounds, clean as a whistle.

Now when I run hot water through it (bench test), the whole thing heats up very well and water flows nearly instantly from tank to tank.

Moral of the story, DO NOT USE STOP LEAK. EVER. If you can't bleed and feed, don't drive it.

TL;DR Back-flushed radiator, discovered hidden stop leak plugging passages. So far, all is well.

[jamal]

You mean subaru coolant conditioner?

[RoughDiamond]

Nope, I used the Peak Cleaner and Flush (semi-causitc stuff) to help break-up the left over "stop leak" the PO put in.

On the subject of the Subaru Coolant Conditioner, the only time I'd resort to using it is to buy time on the EJ251/253 head gasket replacement.

Yes, I've seen it stop leaks for a good amount of time, but it's like keeping a band-aid on a staph infection: It will come back and bite you in the ass at the worst time.

[jamal]

That was a joke about the stop leak that was in there.

[wtdash]

On the subject of the Subaru Coolant Conditioner, the only time I'd resort to using it is to buy time on the EJ251/253 head gasket replacement.

The cynic in me thinks this is SOA's opinion, too....'let's just get 'em past the warranty period'.

HG's are a 'maintenance item' on the EJ25x. Save yourself the grief and do the HG when the T-belt is due @ 105K....not that most people want to spend another $1500+......

td

[macipusy]

'let's just get 'em past the warranty period'

I've always thought the same thing.

[rallyak]

I've seen lots of chatter about 2.5 head gaskets blowing and change them sooner than later. I have not had the issue on any of the 2.5's that I'm running and they have tons of miles on them.

Personally I think the problem is the BS torque on the head bolts. The way they are torqued some make it to 80ft lbs but others are as low as 40ft lbs. From my last build I put inserts in and all my head bolts were 80+ with a solid base to screw in to. So what I'm saying the block is too soft and doesn't get torqued good enough there for blowing gaskets.

[jamal]

Yeah, that could be part of it. Torque procedure did change, although I have used the old on one plenty of turbo cars that had way higher cylinder pressures than an n/a 2.5.

IMO the main problem is the graphite coated gaskets. The MLS version seems to have fewer problems. Even though 2000's era 2.5s still call for the old gasket, you can just get some for a 2.5 wrx/sti and use those instead.

Inserts seem like a lot of unnecessary work. Every other subaru engine uses the same threading and you can put in ARP studs and torque them to 100lb-ft if you want.

[wtdash]

_>>sorry to the OP for the Tangent - glad you got it fixed<<<<

HG: IMHO, it's due to maintenance - but not a lack of normal maintenance. The coolant and oil get 'old' and chew away @ the gaskets, and the oil/coolant need to be changed out more often than recommended in the Owner's Manual/Maintenance Book. It's related to the boxer-design...although I don't know if other manufacturers have this issue. No specific proof on my end, just what I've read over the years leads me to this.

Td

[rallyak]

Inserts seem like a lot of unnecessary work. Every other subaru engine uses the same threading and you can put in ARP studs and torque them to 100lb-ft if you want.

Yes, studs are way better and a more even torque but the inserts wasn't bad. The whole reason I put the inserts in is when I bolted the torque plate down I believe the torque was around 80ft lbs and had a few holes that felt like they were stripping out. For example, it torqued down to 70ft lbs but it took another turn and a half to make it to 80ft lbs. I didn't trust the way it felt and It wasnt bolt stretch, so I put the inserts in.

[RoughDiamond]

That was a joke about the stop leak that was in there.

Yeah, didn't pay close enough attention..

But I have to agree with the argument on the design of the gaskets rather than the clamping pressure. I just think the actual sealing surface on the open deck 2.5 and the graphite gaskets leave little to seal and when they overheat, they have less forgiveness than an MLS version.

There was a theory on USMB about potential air pockets when not filled ideally after a coolant change than allowed hot spots to develop before the thermostat opened and allowed the gaskets to pop, hence you saw very few low-mile 25D motors with gasket issues: they were still factory filled.

Anyway, newer gaskets and filling the block first through the water crossover seems to be the way to go. Haven't seen a repeat offender since.