My son bought a 2004 G35 coupe with a swapped in vq35 rev up engine. It had a lot of overheating issues so in my attempts to fix it I�ve done the following:
-replaced the thermostat and water pump
-replaced the bleeder valve with a metal one
-replaced the radiator although with a relatively cheap one and it was a sedan model (my mistake) but I adapted it to fit the fan
-pressure tested and it held pressure
-bled the system many times
-bought new rad caps but put back the original as the other 3 don�t hold pressure when tested and are all 0.9 bar rated. The original holds at 12 psi.
-tried a RELD test and do not see colour change and the oil looks good.


fluid is filling the reservoir but not returning and there is air in the system as shown by releasing air from the bleeder.

It�s not overheating anymore but that�s probably because I have been bleeding the system very regularly.

I opened the hood this morning and notice what looks like dried coolant residue on the covers for the water pump and thermostat so I am still suspecting that the rad cap is leaking as it�s on the covers and not in one particular area.

I suppose the radiator is crap but I don�t want to buy an expensive all aluminum one yet.

When I opened the rad caps today there was pressure in the system but an obvious air pocket as it hissed when I opened the valve and refilled using a no-spill funnel.

Upper and lower hoses hot. Heat works when bled but cool on idle when flat but warm when elevated.. though that is not all the time..

I�m trying rule out a head gasket issue and my last attempt is getting a 1.3 bar rad cap.

The car isn�t really worth doing a head gasket repair other than the fluid seal type.

Any other ideas would be appreciated.
Thanks

 

Most likely, the radiator cap.
I had plenty of issues with eBay radiators where the cap would go on but not really seal and allowed air to be sucked in during cool down. Those filler necks are cheaply made and the caps are just crap. What i usually do is pinch the cap tabs to make it seat tighter and sometimes apply teflon tape to the filler neck. Get a 'burping' filler device to properly burp the Nissan.
Not sure if you have throttle body heater hoses but if you do, cap them ASAP. My HR tubes had pinholes in them and causes similar issues without any smell.
Also, you can't be sure what was ran through that engine, some people put in that worthless STOPLEAK crap which only blocks cooling passages. I've backflushed many heater cores with a garden hose and seen bunch of crap come out..

 

Thanks! Not sure which hoses are the throttle body ones but I�ll figure it out. Sounds like a good option.
The new mishimoto rad caps came in today so I am hoping it works better. I had tried that trick of bending the tabs on the others and it helped some on the pressure tester but the cap were not great. Even the oem one I bought didn�t work so well so I�m hoping I didn�t waste my money on the new radiator if that�s really the problem with the seal. Just didn�t want to spend too much as I�m pretty sure the water pump and thermostat were ok even though I changed them.
i do have a proper funnel but your comment about backwashing the heater coil sounds like a good idea. If I do that I think I�ll vacuum fill the system.

But I have to change the starter now before getting back to the cooling issues. It�s as lways something.

 

Found a video about those hoses. I�ll take a look.
thanks again

 

You might want to get a higher pressure radiator cap, i had a 17psi on my G35 HR and it ran fine. Lower pressure cap, 0.8 bar wasn't that good here in south Florida. Avoid the once from Rockauto, eBay and Amazon as they claim to the OEM and are not. They leak and don't hold enough pressure.
High pressure radiator cap

 

Thanks. The Mishimoto one is high pressure. Once I replace the starter tonight I�ll bleed the system and test out the new cap. Hopefully this will work.

 

This is what I use on many cars to bleed the system. Fill it 1/3 over, heat up the engine, keep it on 2000-2500 rpm for a minute, let it cool down and that's it.
Bleeding funnel

 

So� starter sorted and back to the cooling system.

New symptom. My son called me the other day saying the needle is up near the top but within the duration of the call it went back down and stayed there. On the drive back from school the same thing happened. I looked at it and sure enough, the overflow had taken a bunch of the coolant but it didn�t return.
I�m trying a different bleeding solution I got from yet another video. Fill until the bleeder cap overflows then put it back on and run until warm and rev up to 3000 for ten seconds several times then let it cool. Repeat and repeat until I check the bleeder and it�s still at the top. I�m on the 5th cycle and each time I�ve had to add less and less fluid.
Before I started I had no heat while idling but I do now. Maybe that�s because it�s not from dead cold but I am hoping.

I found out from my son�s friend that the rev up engine in this was from an accident car so it�s quite possible it has a cracked head. Two RELD tests didn�t show gasses but who knows.

I�ll look again after my son drives it (he drives it pretty hard) and see if the symptoms persist.

I am starting to think that it�s more serious.

 

If the temperature goes up when the car is stopped and goes down when moving around 40MPH, you cooling fans are not working properly. They may spin, but not fast enough to circulate adequate amount of air. I had this issue on my 2004 G35 with the stock original engine. When checking the fans, they were spinning, but the car would overheat when it was stationary and idling. As I would speed up, the temperature would go down. After replacing the fan assembly, all was fine and it has been for the last 3 years.

 

Sounds like an issue with cooling fans if the temp goes up when sitting still... make sure the cooling fans are moving around enough air, especially when the AC is on.

 

That�s an interesting idea but I�ve noticed with the obd scanner that the fans seem to be fine as the temperature gets to 203, the fans kick in and cools to about 185 and they turn off. Never had a problem with that except once after a drive when the coolant was at 216 for a short while so maybe the fans do sometimes stick.. I�ll look more.


But the trouble continues. Did a thorough bleed of the system and was getting great heat and no issues for a couple days. Didn�t overheat but I looked under the hood and the overflow tank was near the top and the coolant level was definitely a bit low in the system as I could not see much fluid in the hose at the bleeder port. Still it did not take much to fill and definitely less than what was excess in the overflow tank.

So my problem with thinking it�s a leak or an engine issue like a gasket or cracked head is that I didn�t get any results from the RELD test and the idea that it�s burning coolant doesn�t make sense as it doesn�t seem to lose coolant, it just doesn�t want to return to the system so air is displacing the coolant. I will try the teflon tape at the rad cap in case that�s a bad seal. Maybe I need a decent radiator instead of the one I bought on Amazon. I will look at the throttle body hoses in a couple weeks as I will be away next week.
I�m tempted to get a better radiator but I am not wanting to keep dumping money into this if it�s really a catastrophic issue.

This is so frustrating, especially for my son.

 

I bought few 'aftermarket' radiators for few cars in my 30 years and they all failed faster than OEM ones. Unless the OEM radiator is over $1,000, you should get OEM, even good used one will be better than those aftermarket ones for daily driving. You can rent a pressure tester from autozone and test for pinhole leaks and you can also see if the filler neck is good or not. Don't delay as that could result in more than just a coolant leak..

 

I�m looking at this one:
https://www.yonaka.ca/ProductDetails...DNG35&CartID=1

better fans and better cooling. I wonder if the plastic filling port is not sealing great under the strain of driving and letting air in rather than returning coolant from the reservoir. I did a pressure test with a set I got from Amazon and it lost about 2 psi over the course of about 45-50 minutes which seems to be okay and likely the tester itself as I can find any leaks. Still not sure though as I�d hate to try it and have the same issues.

I�d like to try a compression test but that�s a bit beyond me.

 

Interesting finding. Took the rad cap off to put on the teflon tape and there was a fair bit of pressure still in the system even though the car has been sitting for about 4-5 hours. That�s the first time that�s happened. I suspect that�s not a good thing and may point to a gasket issue or a cracked head. Ugh.

 

4-5 hours is still gonna retain bunch of heat and pressure. Pressure in the system is good, unless it's vomiting, then it's not good. You should smell the coolant to see if it smells like burned gasses or discoloration. Seal that filler neck and have the car sit overnight.