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Help! We purchased a 2008 Honda Odyssey (~36K miles) from a reputable dealership in Ohio about six months ago. The engine light first appeared ~6 weeks later (voiding the dealer warranty). After relocating to Virginia, we took the van to a local mechanic, who scanned the engine and noticed a “random misfire code” on 5 of 6 cylinders. He drained the gas tank, thinking we may have bought some bad gas during the move, and the engine sounded better for a day or so. The light reappeared the next day and the engine continues to run poorly (especially during start-up/high speeds on hot days). I started noticing poor AC performance/an over-active engine fan after the engine turned off. We took the van to a second mechanic, who confirmed that we were ~2-3 quarts low on coolant (which seemed to fix the AC/fan issues). But we haven’t noticed any drops or puddles of coolant on the ground, and the local Honda dealership claims that the coolant system holds pressure during a block test. The coolant overflow level never seemed to drop while the coolant was low, so we replaced the radiator cap (which seemed to fix that problem). The dealership then recommended changing the spark plugs and getting a fuel system “induction cleaning”, which improved the performance a little. We just had the oil changed last week, and noticed a black grainy sludge at the base of the oil pan, though the oil has been changed every 3000 miles according to maintenance records. My hunch is that the coolant might be leaking into the oil through a pinhole crack in the head gasket. But we haven’t seen any milky deposits in the oil (only sludge).
So to recap:
1) Engine light (random misfire code on 5 of 6 cylinders, confirmed by 3 different mechanics)
2) Coolant leak (~1 quart every 2 weeks) and burning coolant smell (no puddles, coolant system holds pressure)
3) Oil deposits
4) Shaky engine at start-up and higher speeds, especially on hot days
We haven’t been driving the van very much and would like to avoid killing an almost-brand-new 40k mile engine. I’m a little worried that something might have been damaged when the coolant was low (head gasket, etc.), but we can’t explain the high coolant system pressure or the gunky oil. We live in rural Virginia, so our repair options are pretty limited. Any advice would be appreciated!
 

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1. Read the thread on random misfires on this site. There is a lot of diagnostic information. Pull plugs and look for carbon buildup, signs of misfiring.
2. If you smell it burning and are loosing coolant there is a slow leak somewhere. You need to closely inspect everywhere for signs of the burnt coolant. It may be dripping on exhaust somewhere.
3. some sludge around the drain plug is normal as long as there is no sign of water contamination.
4. Back to 1. It could be a fowled plug, bad injector, bad coil, etc
 

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Engine light doesn't void the dealer warranty. If you bought a 100k warranty, it's still in effect.

As for the coolant, the only thing I can think of that could cause crappy early morning running, sludge, and high speed crap running would be by the cooland radiator in the intake throttle body right next to your idle air control valve. Open up your throttle body and see if you find any coolant in there. If you do then it could be a bad seal on the idle air control valve or even the radiator inside the throttle body itself. It might be a good time to check your egr port and pull out the intake manfiold with it. You'd see green or very clean in the intake manifold ports of cylinders 6 and 5 closest to intake if its the case.. I doubt it would even smoke if its got a tiny leak there since the pressure is so low through there.

This might actually be covered under the emissions warranty. Take pictures as you take it all apart and use it in a letter to honda, they may give you something out of it.
 
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