2006 Coupe with engine problem

[jerry119]

I have a 2006 Coupe with about 112K miles, auto trans, that I bought used about 6 months ago, that started overheating. No external leaks but will overheat after about 45 minutes - 1 hour of extended highway driving, overflowing coolant into the overflow tank and pulling it back into the radiator after cooling down, usually requiring adding coolant to the overflow tank. Will not hold pressure when the cooling system is pressurized. Does not use coolant or overheat when driving in the city - only on the highway at continuous speeds. Never overheated badly to my knowledge. Does not appear that water is getting into the oil. Took it to a local dealer suspecting a warped head or bad head gasket. They want $3500 to replace head gaskets, or as much as about $15k for a new engine, but they are not really sure to what extent it is damaged (may be a block problem too). My thought is to buy a used engine for same or less money. Ideas? Would a newer G37 engine fit without serious problems - accessories, trans, etc? The car is almost worthless without an engine and I still owe on the loan. HELP! Thank you...

[telcoman]

I have a 2006 Coupe with about 112K miles, auto trans, that I bought used about 6 months ago, that started overheating. No external leaks but will overheat after about 45 minutes - 1 hour of extended highway driving, overflowing coolant into the overflow tank and pulling it back into the radiator after cooling down, usually requiring adding coolant to the overflow tank. Will not hold pressure when the cooling system is pressurized. Does not use coolant or overheat when driving in the city - only on the highway at continuous speeds. Never overheated badly to my knowledge. Does not appear that water is getting into the oil. Took it to a local dealer suspecting a warped head or bad head gasket. They want $3500 to replace head gaskets, or as much as about $15k for a new engine, but they are not really sure to what extent it is damaged (may be a block problem too). My thought is to buy a used engine for same or less money. Ideas? Would a newer G37 engine fit without serious problems - accessories, trans, etc? The car is almost worthless without an engine and I still owe on the loan. HELP! Thank you...

Did the dealer perform a compression test to confirm a leaking head gasket?
Was the water pump, thermostat, and fans tested? What about a loose belt?
Try another dealer for a second opinion
Good luck

Telcoman

[jerry119]

Telcoman, thank you for your reply. There are no external leaks, hoses and belts good/fairly new. It only overheats when continuously driven at highway speed for about 45 minutes, then the temp. gauge starts to fluctuate a little and moves up to just past center. Around town - no problems. Dealer basically not sure - says it could be a head or head gasket, and the only way to tell if it is that or maybe a cracked block is to tear into it. The cost is about $1500 to get the head off (labor charges) and may then only find it is a block problem. Th car is no problem if not driven on the highway for more than about 45 minutes - a 20 minute highway trip shows no problems. It's the continuous high speed driving that leads to the problem.

[audtatious]

Any foam or milky color when looking at your oil? Sure sign of a HG problem. If not, then it's probably not a HG.

[joe603]

+1...and if your oil capacity goes up...another sure sign that you have a HG leak.

If you can confirm that it's not a HG leak, I would completely flush the system and replace the thermostat.

The 3.7L engine would be a project to get it to work...I'm sure it's been done, but probably using aftermarket ECU/components...AUTO trans is different in the 3.5 vs. 3.7 (7-speed in the G37)...that may not play nice.

[audtatious]

must not forget white smoke and that nasty-burnt coolant smell from the exhaust

[jerry119]

Thanks to all who have helped - I have a couple things to check again. Guess I will not consider the 3.7 - sounds like too much for now.