P0117 and P0304 Codes (Protege5)

2003 P5 AT
Apologies in advanced for the long post.


Son and his P5 stranded in rain with overheat. Topped off radiator and overflow. Take surface streets home. New radiator cap seems to have fixed it. Engine runs well, no more codes. See below for more details.

What temp does your P5 normally run at?

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Son is on his way home yesterday during a big rainstorm. He was about 30 minutes out in heavy traffic when his CEL came on and coolant temps gauge pegged rather suddenly. He managed to limp off the freeway and into a nearby strip mall parking lot. Calls me, tells me what happened. He carries a cheap code reader and told me the 2 codes. Since one related to coolant, he checked the overflow bottle and it was empty. The Temp warning light never came on. OK, so far not good.

So I pack up some tools, my better scanner and about 1.5 gals (6 liters) of coolant and head out. It's still raining when I get there but the car has cooled off. Pop the rad cap and I see no coolant. Go to top off the rad and it takes nearly 2 quarts. Still raining out. Start the engine, seems to run fine. Continue topping off the rad, takes about another 1/2 quart. Let it run for a few minutes, still getting some bubbles in the rad. So we decide to put the cap back on it, top off the overflow, stick to surface streets and head home. I drove it and kept my scanner connected to watch the live data. I cleared the codes before we left.. My son followed me in my car. About halfway home, the rain stopped, sun came out. I took it as a good sign. Managed to get home without further incident.

One thing to note was the coolant temp indicated on the dash stayed around the middle of the range. My scanner reported temps around 224-228, reaching 230 for a brief moment at a traffic light. I almost pulled over to call a tow but the light turned green and as we moved the engine cooled a bit.

So we get home, I pop the hood with the engine still running, and I can hear and see the coolant bubbling in the over flow tank. Dang!! After cooling down I pull the radiator cap and the radiator's still full. I should note that once the rain stopped and we got closer to home, my son did not observe any smoke coming out the exhaust.

At this point however, I fear he may have blown a head gasket. While I do have a compression tester and a leak down tester, I decide to do the block test with the special liquid. Since I don't have one, I'll get "rent" one from my local auto parts store. While I'm there I'll get a new radiator cap as I never reuse one that's overheated.

So off to the first autoparts store. I checked online first to see if they had them in stock (they did). Parts guy gets the cap but reports the tester is not there. OK, so I grab the cap and head home. Turns out the cap doesn't fit, it's too small. Go back online and discover caps for autos are different from manuals. Mine's an auto, cap was for manual. So I check another store (different company), see they have the right cap in stock and the block tester. So off again with my old cap in hand. This time it's the right one, but the block tester is not there. The do have the radiator pressure tester (the hand pump) so I "rent" it.

Get home and to my surprise, none of the adapters for the pressure tester fit. I admit, I laughed a bit. So with the rad topped off and the overflow filled, I started the engine and left it warm up with my scanner attached in live data. I carefully watched as the temp climbed. With an occasional 2000-3000 rpm blip, the engine temp stabilizes at around 212F. The electric fan kicks on too. Also, there are no codes, in fact the drive home was enough to reset all the readiness monitors.

So I climb in and drive around the local streets, just in case. Car runs fine. Temps touched 213F once but remained pretty much at 212F with an occasional drop below 210F. Got back home, popped the hood, looked at the overflow bottle and there's no bubbling, the level looks good. Shut it down, left hood open to cool down. Came back out, coolant overflow level still good. Took rad cap off and it's still full.

Hmmmm.... Good sign?

While I may order the block tester online and still do a compression/leak down test, that won't happen today.

So at face value, it appears the issue was a bad rad cap? It lost pressure, then lost coolant, the low coolant triggered the P0117 code. The bubbling coolant in the overflow was just the rad boiling over due to the bad cap? While possible the high temp caused the misfire, his P5 does occasionally trigger the same P0304 when he drives in heavy rain. It still runs OK, and the CEL usually goes out once he's out of the rain. He changed the coils out last year (while he live in another state) so I think the misfire is more coincidental to the rain and not the overheat. Going to do some more local driving with it today (local errands like returning the wrong cap and tester) with my scanner hooked up.

At what temp does your P5 run? FSM indicates 212F is thermostat full open.

Any opinions on the rad cap being the cause of the problem? Given all other live data looks good and no codes after about 30 miles of driving (just enough to reset readiness monitors) and engine runs well, do you think we're OK? The other tests will have to wait until later this week. We do have a spare vehicle him to use while we figure this one out.

How does you oil look?

I would do a cylinder leak down test to eliminate a head gasket issue.

Bubbles in the overflow can indicate a leaking head gasket...

Good Luck
Oil looks good. No sign of coolant. Coolant looks good. No sign of oil. No more bubbles in the overflow tank either.

Ran a few errands with it this morning. Back to parts store #1 to return cap. No issues. Temp remained around 212.

Then back home to get tester and return to store #2. Same results. Oil still looks good. Overflow tank is “full”, no bubbles. Radiator is still full. Son took it out for his own errand locally. Says it runs like always.

Still plan to do block test and leak down. Going to order some plugs to replace while I have them out.

When our Subaru block cracked it would overheat. Then run awhile before the crack opened up again. We put Blue Devil, Liquid Glass, in the cooling system. It held until we traded it in.

I've used liquid glass to fix water leaks. It held up very well. I hope you don't have a cracked block...
210°F is probably a little bit high for those engines. Sounds like the cap helped. I would maybe plan on replacing the thermostat. It might be starting to fail, and isn't opening like it should. I thought normal engine temperature is ~190-195°F