possible overheat/stumbling issue at idle
 

Hey everyone,

so as the title of the thread suggests I may possibly have an overheating issue. I've had overheating issues in the past and had them taken care of by changing out a bad thermostat, however, recently I changed out the spark plugs on the car with a fresh batch of OEM denso spark plugs after having a set of NGK spark plugs go out on me prematurely due to a parts store and NGK having the wrong spark plugs listed for the 370Z. car ran great after I switched out to the oem denso...fast forward to a few days after I installed the correct spark plugs and im starting to get an intermittent stumble of the engine RPM's at idle, checked what the engine was up to through a scan tool I have and discover that the short term fuel trims are hanging at or close to 25% for a good 30 seconds and then the engine stumbles and the fuel trims correct themselves back down to near 0%. thinking that maybe it was just the engine clearing itself of some carbon buildup from having the wrong spark plugs in it I drive around for a few miles after this and everything is working fine. next day which was yesterday with temps around 80 degrees outside I decide to turn on the AC and just happened to have my scan tool opened up on my phone to keep an eye on things. oil temps were around 200 and had just gotten off the freeway and parked to go visit a friend and sat there a few minutes to watch what the car would do. next thing I know im seeing coolant temps start to climb over the 220 mark with no sign of the oil temps dropping despite the radiator fans being on full blast. shut the AC off, radiator fans still going and coolant temps start dropping off back to normal and drop even further after I open the hood of the car. so my question is this....does anybody have any idea what the heck is going on?

How many miles on your car? Probably time to clean your throttle bodies

Also, you have an oil cooler right?

cleaned throttle bodies while I was changing spark plugs and yes I have oil cooler. oh and 132,000 on engine

forgot to mention other maintenance items I've replaced on the car before hand....O2 upstream and downstream sensors have been replace, MAP sensor has been replaced, MAF sensors are still good and reading within spec, catalytic converters have been replaced, throttle bodies have been cleaned, coolant has been flushed and radiator cap and thermostat have been replaced and of course last but not least, spark plugs were replaced. all parts and fluids are OEM spec in case anyone had questions about that

You have a clogged up radiator, or ur pumps propeller? Ran dry maybe and destroyed it self, basically it's laking in cooling.

Short fuel trim is for start up of the car till all sensors heat up and start sending proper info.

The cooling when you pop the hood leads me to believe that you have a problem with air flow across the radiator. Confirm that the oil cooler or other items are not blocking flow through the radiator. Check condition of fan blades and that they fit in the housing properly (efficiency is reduced if the fan is too far forward or back in the housing). Check fan motors for proper speed. Make sure air is able to exhaust through the transmission tunnel.

The 370Z runs hot - the cooling system is marginal from the factory. You may need a bigger radiator and/or fans.

Your definition of short term fuel trim isn't incorrect.

Apologies for reviving this from the dead, haven't really messed too much with the Z since this and she runs great....been through a few more diagnoses procedures to check and make sure everything was ok engine wise, leak down and compression tests done along with pressure testing the cooling system and everything checked out as in good order. Overheating issue still persists though and it's really strange cause it's only in a very specific situation that it does this and I'm thinking it does have to do with the cooling fans, only thing I'm unsure of is how to go about testing the fan speed as you suggested. I'm wondering at this point though if it would just be better to get new fans and hopefully just be done with it though.

Hmm, guess no one is active on here anymore

You come back to a 4.5 year old thread and "we're not active on here anymore"? :rofl2:

Well, i mean it did take over a week for you to respond to this thread :rofl2:

according to your OP, sounds normal. How hot did the coolant get before you shut engine off?

The 50/50 solution should boil around 240-250F. Did you notice if it reached that high? (obviously you may get a boil over) Temp drop after fans ran for a while?

As for your oil temp., it will continue to rise if you are just idling with no airflow. Oil cooler or not.

So 80F outside, you drove on highway till oil temps around 200 and then idled for xx minutes? What did you think will/should happen?

First time it happened coolant temps reached over 240, temp gauge on the dash was just at the dot before red... haven't let it reach that high again at the risk of damaging the engine..... the Z never exhibited this behavior before i had a dealer swap out the engine coolant for the first time in my ownership of the car, more than likely just a coincidence. I've tried flushing and burping the system multiple times since then and even had it vacuum filled but no luck there, kept on getting told possible head gasket issue from different members on the forum which is why i had a leak down and compression test done on the engine which came back with a clean test. Car cools itself off fine even when idling so long as I'm not using the AC, hasn't been a high priority for me since i have another car that the AC works fine on that i can use on hot days so this has been put on the back burner for quite a while