The inlet tank of the radiator had a hairline crack which caused the car to overheat. Got the tank repaired and filled it up with new coolant. From what I can tell I don't have any major issues when driving the car. Things are still peachy.

Only when I turn on the car the first time in the morning or after 6 hours or more from shutting off the engine I get a rough idle for about 5-8 seconds and then the car straightens itself out.

I have codes

P0300 - Random Misfire (after the overheat)
P0303 - Misfire cylinder 3 (after the overheat)
P0305 - Misfire cylinder 5 (after the overheat)
P1316 - Engine Misfire (after the overheat)
P0420 - Catalyst efficiency below threshold bank 1 (had this issue since I acquired the car)

I just changed all 6 spark plugs earlier in the year so I'm guessing it may just be the ignition coils. I heard that these go bad often.

Also, is there a way to tell if the head gasket could be blown as well? What would be a tell tale symptom of a blown head gasket?

What else should I be looking for after an overheat?

Thanks.

 

We need your car's details to help you better get to the root of the problem(s)

Post year, engine and mileage.

Here are a few guesses...

- Like you say, head gasket
Do smell engine coolant? White exhaust smoke coming from tailpipe? Engine oil milky?
- Check coils and plugs and if OK - Catalytic converter(s) may have failed (possible, but not likely the problem)

 

Thanks 1320racer. I have a 2004 s type automatic with 167500 miles, no white exhaust smoke or milky oil. I do smell engine coolant but it's subtle and it's getting lighter. It's probably from when the coolant got everywhere when my radiator broke.

 

Again we need the car details?

ALL of them like what engine is in it! You said 6 plugs so I can guess but help us out here. We are a LONG way from you.
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Whoops sorry. I usually do not overlook that part. The engine is a 3.0 V6

 

It's probably not the head gasket (though it could be). More likely a bad coil (swap two and see if fault moves or fit a good new one) or even an air leak (check fuel trims).

 

I would forget the head gasket and focus on the known problems of the 6 cylinder cars.

Vacuum elbows and lines rotting and leaking. IMT valves leaking oil.
And of couse with the age of the car plugs,coils and intake gaskets.

Be aware that if the car has been driven a while with these misfires you might need to replace the cat. That is one of the problems with people who just keep driving. If you catch it quick enough then the cat should be OK.

Fix the other problems first then see if the Cat code comes back.

Have you cleared all codes to check what comes back?
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Good advice. I will change the coils and change the intake gaskets and the IMT gaskets at the same time. I dont have a device to check fuel trims, but I can tell you my fuel economy has suffered greatly 14% decrease in miles to the gallon. I have not cleared the codes yet because the misfires happen every morning. Those codes will come back, but ill try it this weekend. Unfortunately I don't think I can source the parts and get the job done this weekend.

 

Bad fuel economy = panic. Unburned fuel is destroying the cats.

 

Here is an update. I looked at the spark plug and saw #3 had a bit of oil on it and #5 was really bad( dark slimy gunk) I replaced the coils on that side and the spark plugs. It ran fine for two days and then i started seeing misfires again on the same cylinders and white smoke coming from the tail pipes.

No milky oil yet, but i assume i have some coolant leaking into the cylinder. I ordered the head gasket and IMT valves and they should be here tomorrow for a weekend job. Any other gaskets I should change while I'm in there?

 

I would recommend doing both head gaskets, both heads, and all gaskets north of the block line.


That's a job!

 

Other gaskets needed:
- valve (cam) cover (2)
- lower intake (6)
- plenum (upper intake) (6)

All above gaskets (seals) can be purchased from a big box auto parts store. FelPro is the brand.

Be careful of the quick connect for the brake booster vacuum located on back of plenum.

 

Have your block deck checked too for straightness. If you put newly finished heads on a warped block you're back to where you started.

 

Thanks everyone for the input. I held off on fixing the intake gaskets so I can plan out this large head gasket job during Thanksgiving break. I'm so bummed right now. Any of you have come across a diy?

 

Confirmed a small Head gasket leak. Fixed it by using Blue Devil Head gasket sealer.I saved at least $1200!

I also changed the IMT,valve cover, upper and lower manifold gaskets a few days after using Blue Devil for preventative maintenence.

For being over 190k on the odometer this cat starts up like a brand new car. With no misfiring or vibration. I'm happy that Blue Devil worked for me.

 

I would normally scold you for using that stuff, but with 190k miles on the odometer, what's the difference?


Good solve!