Hello all, I'm new to the forum so I apologize if this isn't categorized properly. I have a 2007 G35x with the 5 speed auto.

I did my 90,000 mile service two months ago at 85,000 miles including a tranny flush and coolant flush. A month ago at 87,000 miles, my check engine light came on and it was determined by my mechanic that a thermostat went bad. At that time, he noticed a little oil in my coolant and did another flush to see if it came back. At that time we thought the problem wasn't coming back as 3 weeks went by with no sign of oil in the coolant.

Just this week at 90,000 miles, a hose popped off the coolant reservoir spilling all of the coolant. What was worse was that it looked like more oil than coolant sprayed all over the engine bay. I towed the car back to the mechanic where he replaced the hose (which likely deteriorated because of the oil in the system) and topped off the coolant. He said he ran it and drove it for a while with no signs of the oil returning. I picked it up and drove home that night. No issues of overheating, etc. The next morning I checked the coolant and it looked dark so I returned it to the mechanic.

He is now convinced there is oil getting into the cooling system and sees two possible areas of issue... the more severe and obvious one being the head gasket, and the other being the oil cooler. However to my knowledge, the oil cooler is a closed system which wouldn't allow the oil to touch coolant with a bad gasket or O Ring, etc. The oil cooler would literally have to have a hole in it for oil to mix with it.

The mechanic is looking at $2500-$3000 to replace the head gaskets.

Does anyone have any thoughts? I tried researching others with similar problems/people with blown head gaskets in this engine and it seems pretty rare. $2500 to replace a head gasket also seems very high. I'm based in NY and the labor rate hovers around $120 an hour.

Any help would be appreciated.

Thanks!

 

It could also possibly be the water pump there are two o-rings that separate the oil and coolant from mixing. The oil cooler is where the filter screws on I don't think there is a way for the two to mix, since if that o-ring goes bad it's usually oil that leaks out.

When was the last time you changed your oil? Did it look like chocolate milk?

Did the car overheat at all? Have him do a compression test or leak down test before jumping into the head gasket....sounds like he wants to make some money.

 

I'm getting a slow leak of coolant into my oil so I will have to check this. Thanks!

 

Yea, it's not something I would have thought of either until I did my timing chain/water pump job. I do know that since I didn't drain the block of coolant when I pulled the pump out it filled my engine block up with water/coolant. So, it definitely is a source of oil/coolant mixing together if those o-rings go bad.

You can also rent a block tester from AutoZone for like 30 bucks. You drain some coolant out of the radiator and then stick this device on top and suck in air checking for exhaust gas. The color changes colors from blue to green/yellow.

 

Car has never overheated. Oil looks fine but the coolant looks like chocolate milk.

 

Oil in coolant = blown head gasket, end of discussion! You might shop around and see if you can get it done at a better price. You'll also need your coolant system flushed to remove all the oil residue! Since you have a V6 changing just the side that's blown is all you need! Call your local Nissan dealership for a quote.
Gary

 

I'd still have a block test and coolant pressure test then if you're getting oil in the coolant. You can do both of those one your own renting the tools from Autozone and Advance Auto.