Hey guys. I have an 5AT '04 G35 Coupe with 112k miles. I recently got it and it runs fine, shifts smooth. But there are two things that really bother me

1. The tranny fluid is light brown, smells kinda funky. Not burned, but not fresh either. I have no information if previous owners changed the fluid or not. So is it needs to be replaced asap?

2. The car temperature is normal, only there is almost no hot air, so heater core is most likely clogged. Coolant is muddy and needs to be replaced. I took it to Infiniti dealer and they said that there is Stop Leak in the coolant, so flush might expose leaks and make my life much worse. They suggested a flush, compression test, and full diagnostic of the cooling system for 450$ which is a lot for me. Previous owner replaced the radiator cuz it overheated once and his mechanic blamed it on a clogged radiator but he doesnt know about stop leak thing...
What would you recommend?

 

Let's begin with your major issue, find an independent Nissan mechanic to trace down the issue with your radiator. Any time I've seen radiator fluid that was "Muddy" there was always a head gasket blown, hope that's not your case! Stop Leak, they're assuming that's what it is! Transmission, just do a drain & fill using only Nissan fluid...Gary

 

Wow, first off your tranny fluid should be red and nowhere near looking brown. The coolant should never be muddy either. Sounds like someone is leaving out information either the mechanic or the previous owner.

What does your engine oil look like? Chocolate milk?

If I were in your shoes this is what I would do:

Buy Nissan Coolant
At least 12 qts of Nissan ATF or something compatible (I use Idemitsu Type J)
New radiator

Maybe
New thermostat
New water pump

In this order.

1. Check the two hoses in the back of the engine going into the firewall make sure they are not connected to each other. I never used stop leak, but maybe he didn't connect them back up and that's why you're not getting heat. If it is then go to the next step.

Disconnect the hoses from the firewall or coolant pipes to clean the heater core out.

2. You can try to back flush the heater core with compressed air or water on low setting to get all the antifreeze out. Then dump some CLR in there and push it out again to see if that helps clear it up.

3. Get rid of that coolant ASAP.

4. Take out that radiator and put a new one in. I got a replacement for 60 bucks on eBay about 2.5 years ago and still going strong.

5. Try flushing the engine block out with some water or compressed air on low setting to get the remaining junk out.

6. The radiator also cools the transmission fluid, since you said it was brown I'm hoping it wasn't mixing the antifreeze together. You'll want to do about four drain and refills on your transmission fluid every 50 miles or so. Do it when the fluid is cold, measure the amount taken out, and put the same amount back in.

7. I'd take the thermostat cover off and inspect that also to see if it's in good condition.

8. You can also take the black cover off on the right side and make sure there is no gunk in the water pump. You'll need to reseal that back up with some RTV though.

You can do a compression test on your with a 20 dollar kit from harbor freight.

 

God dammit, I have incoming midterms and I cant calm down now D:

Nothing really indicated blown head gasket. Oil is completely fine, no white smoke, no loos in coolant. And I jut opened the coolant reservoir and puled out some with a straw, its fainting green. In the radiator cap there is some rusty looking build up and the fluid has some particles in it

 

You can have a blown head gasket and not have water in the oil! You can also have oil in the radiator which is what that brown/green crud looks like on the opening and cap. Compression test will prove my vast knowledge is correct and it is what the dealership recommended...Gary

 

So I must flush the coolant asap? Do I have to use Nissan coolant exclusevly? No ther alternatives? And if that opens up head gasket problems I'm pretty much screwed, I cant aford to fix that problem now...

 

Go to Harbor Freight and buy a compression tester it's like 20 bucks. Go to AutoZone and ask to rent their block tester for an additional 20 dollars. For forty bucks you can check the compression of your engine and check for hydrocarbons in your cooling system. Then move on from there with the radiator, ATF fluid, etc..

 

block tester didnt show a leak. I did a flush with a help of my friends mechanic (coudlnt do it myself cuz live in apartment with strict rules). I drove car pretty hard for 50 miles, temperature stays in 180-191F region, next is to check it in LA traffic in next few days haha. Heater core was not really clogged, and still no heat after a flush. Could it be stuck blend door or something?