chris'smax

iTrader: (5)

Driving home from work the other day (40 mile trip, mostly interstate) my car suddenly started overheating by the time i got home. Temps were fine on the interstate, but after doing a couple of boosted runs 10 miles from my house i noticed the temp gauge went up. When i backed off the throttle and continued cruising at around 50mph the temps went down. When i got in my neighborhood where i was driving at low speeds and stopping frequently at stop signs the the temp gauge shot up to the 3/4 mark on the stock temp gauge. I pulled in my drive way and as it idled the temp climbed a tad more so i shut the car off and popped the hood. I discovered that the coolant was boiling in my overfill bottle and noticed what sounded like boiling noise inside the radiator. After about an hour of letting it cool i went back outside and started it up and the temp gauge showed its usual reading and i confirmed both fans were running. Also checked the heater and it was immediately blowing hot air. I then let the car cool for 3 hours and looked at the resivoir and the levels had gone back down. The ambient temps were above 95 degrees that day so it was deffinetly hot, but i have had this setup for close to 4 years and never experienced this. My immediate assumption was a headgasket leak, but when i built my motor i used 1/2" headstuds and a hks headgasket and the car has maybe 10,000 of nothing but low boost mileage (9.5 psi, car is tuned to 21psi) so i would like to think this isn't the case.

In summary:
High temps
high overflow fluid level and boiling fluid
heat blows hot
both fans work
fluid levels in overflow went down after car cooled off.
no smoke from tailpipes
coolant not milky
oil looks fine

My next course of action is to bleed the system, check the temp of the lower rad hose, check the thermostat, and do a chemical analysis on the coolant to check for exhaust gases. Any other ideas of things to check or ideas of how a air pocket would suddenly present itself after this long?

eta: Car is running stock fans and rad and no oil cooler. Only cooling mod is pathfinder cooling mod. I have a mishimoto rad/fans and earls oil cooler waiting in the garage to put on.

djamps

iTrader: (1)

Not sure what kit you have, but the APS kit is known to boil the coolant in the return lines. Aside from that most likely a intermittent HG issue.

chris'smax

iTrader: (5)

i have the sfr kit running hks fcon.

djamps

iTrader: (1)

Sleeve dropped?

chris'smax

iTrader: (5)

nope stock sleeves.

Would the chemical test for the coolant give me a 100% answer on whether the headgasket blew? I am thinking that is my best form of testing.

fklentz

iTrader: (5)

I had exactly same problem. If I just ignored the radiator I would loose a little water everyday, if I kept the expansion tank filled it would pull in enough to prevent a problem. When I ignored it the expansion tank would eventually suck in air and it would overheat.

What I did was use a stant pressure tester, fill the radiator and pump it up to 15 psi and look for leaks, you may find a small drip when it's cold that boils off when the car is warmed up. Mine was in fact a head gasket leak, found when SFR rebuilt engine. I had no water in the oil issues, but when I boosted the engine I could smell coolant right afterwards.

superchargedg

iTrader: (4)

Yes it will

chris'smax

iTrader: (5)

This is what I found in my overflow bottle. Particles seem to be magnetic

djamps

iTrader: (1)

Looks like ur HG is done. The metallic stuff could be the HG itself. Not sure what other metal would end up there unless the water pump is eating itself up...I don't think I've ever seen a failed water pump on a VQ.

chris'smax

iTrader: (5)

Yep agreed. Still going to do a chemical test to confirm. If it is blown I am parting this ***** out and doing a ls1 swap.

djamps

iTrader: (1)

Was the car actually tuned at 9.5 psi (you mentioned actually tuned for 21psi)? I wonder if you had detonation or other tune problem such as running very lean... at 9.5psi a stock block/HG should hold up in fact I've been running 9 lbs for 4 years and 30k mi.

chris'smax

iTrader: (5)

Car was tuned via fcon vpro from 7.5psi to 16psi on 93 octane. 19psi to 21psi is done with q16. The car has been tuned for 4 to 5 years so so I am leaning towards mechanical failure moreso than tune(but hell who knows). I am about to go get a testing kit and see if it is blown or not. If it is I have some decisions to make on which path to take next.

djamps

iTrader: (1)

If it's just the HG it shouldn't be too much work to redeck/replace it. Beats rebuilding everything. But I'd still look into your tune and make sure it's not too lean or pinging. I doubt headlift was the issue given the 1/2 studs...

2004Black350z

iTrader: (37)

+1 on gas test. It will tell you exactly if it is HG. We use them on occasion awesome tool for diag