Hey everyone. I haven’t been on here in many years. I’m an original owner of a 2004 G 35 coupe in mint/collectors condition with only 80,000 miles. Because I have trouble reading well while I battle astrocytoma, I need help since I can’t find an answer to what my car is doing.
I just had the two new fans (OEM) put in by the Nissan dealer and whether it’s a coincidence or not, it seems the engine is getting very hot with only 30 minutes of no traffic, 40 mph travel. At idle, I can hear fans kicking on and off every couple minutes. When I pop the hood, even grabbing the Bar to hold the hood up is burning hot. And yet the gauge shows stable in the middle for engine temperature. Also, I smell strong coolant odor but hope that’s just some extra splash from when they changed the new fans.

Please help, and I look forward to any advice or answers.
Tobe

 

When I first bought my 2004 sedan I noticed the same thing happening. I'd drive to work, and within a minute of being parked, the fans would turn on. I have a scangauge-2 to keep an eye on engine vitals.
My fans turn on low speed at ~204*F, and high speed around 208*F. The water temp was always typically between 185-200*F. When coming to stop in traffic, the water temp would go to 204 and trigger the fans ~ 1 minute.
I replaced the radiator, radiator hoses, heater hoses, and the thermostat for preventative maintenance. I ordered everything off of Z1 motorsports, save the CSF radiator I bought from Rockauto. After replacement, I noticed the water temp would run around 175*-190*. I was confused as hell for a week trying to figure it out, finally cross referenced the part #. Turns out, Z1 sent me the t-stat for the 6mt cars, which are 170*; 5at cars are 180*. Z1 only stocks the 6mt one.
With the 170*, my fans comes on after running the car hard (iex canyons, WOT pulls) or sitting for more than 5 minutes (traffic). At first I was concerned and was going to order the 180* t-stat. But, I tend to run my car hard, so I think the 10* lower temp unit works in my favor overall.


FYI The coolant temp gauge on the dash (at least for both my G's) stayed in the same spot anywhere from 170* to 210*F.
If you smell coolant, then you need to search for leaks. Thoroughly clean the engine bay to remove any coolant stains, then drive the car and look to see if any appear. Using a cooling system pressure tester is a great way to check as well.
Your miles are low, but rubber doesn't last forever even with low usage.
These cars are notorious for air pockets in the cooling system. I would try bleeding the cooling system, any air in the system reduces the cooling efficiency, which could explain why the car is getting hot quickly. Make sure your heater is blowing HOT air with the car idling @ operating temp.
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Thanks so much for the response! Although I don’t understand everything you were mentioning, I will start trying to research it and look into it. Any repair I’ve ever had done to this vehicle was either by the Nissan dealership or a master Mechanic that specializes in imports.
I wonder if it’s possible one of them used an aftermarket thermostat like you mentioned and that’s what’s causing it to get hotter than an OEM part?? And since you mention the meter doesn’t change within the temperature range you showed, is it still safe for me to keep things the way they are, even with the fans kicking on and off during idle, or should I look at having someone replace the things you mentioned with OEM parts?
Sorry if I didn’t mention everything correctly but I’m doing the best I can :-)

 

I've heard that the aftermarket thermostats (autozone, pep boys, etc) for these cars are terrible. They can stick closed even when brand new, and cause overheating issues.
I'd say your safe to drive the car as it is, the engineers designed it that way. BUT definitely investigate the coolant smell you mentioned earlier.
If you replace parts, I'd only recommend using the OEM or the Nismo thermostats. For hoses and the radiator, aftermarket is sufficient.

 

Thanks Andrew! Your answers have given me peace of mind and great advice. I am cleaning off everything I can so I can check again if there’s any leakage from the coolant. And from what you mentioned, I won’t be concerned as long as My temperature meter stays in the middle. This has been great help! And I did expect to use just OEM parts and make sure either place I go will use nothing else. Since I just had the OEM fans put in, I hope they will last a long time, even as they kick on and off in idle.

 

Get a pressure tester from a parts store, test both the cap and the radiator.

I'm pretty sure what's happening is you have a minor coolant leak which is causing the system to not properly build pressure which is causing the system to be worked harder than usual.

The cooling system is adequately sized to handle a LOT more abuse than normal daily driving (oversized sports car cooling system) and thus the engine isn't overheating YET.

I don't think your thermostat is the issue since it's apparently opening properly, if you do end up replacing it I recommend getting the Rev-Up / Nismo version. it opens at 68 C rather than 76 C. Excellent if you live in a hotter environment or do plan on taking the car to the track.

 

Thanks for the tip of what to test and the Nismo. The Nissan dealership claims they did a pressure and thermostat test while they were doing my new fans but I’ll have to see exactly what they did.

 

Have you checked the coolant level in the radiator AND the reservoir?

If you just got the fans installed in the last week then you might actually have a little bit of a bubble left in the cooling system that the dealership didn't completely remove. Normally dealerships are really good about using a vacuum coolant system tool which I've had EXCELLENT results with but sometimes they just do it the old fashioned way which is easy to trap air on the VQ.

Turn on your heater to full hot and full fan speed next time you go for a drive, rev the engine out a few times as well. Just roll down the windows or open the sunroof to manage your inside climate because it's going to get really hot in the cabin.

If it's NOT blowing insanely hot air then you definitely have air trapped in it and the dealership screwed something up, call the service manager if that's the case.

 

Thanks again! You and Andrew have been a lot of help. I’m going to test what you mentioned when I drive it in a couple days iand decide whether I should get Nissan service to look at it again. Either way, I will keep you updated. Thanks again.

 

Also something you might not be aware of, anytime the AC is turned on the radiator fan speed will automatically switch to full on high. Not sure if this applies to the defroster but I assume it would because it also turns on the AC compressor during defrost mode.

 

Here is my update from today.
Drove in about 20 minutes and did the heating at 90 with the fan all the way up as you mentioned. Heater consistently cranked out very hot air. When I got home, no doubt the engine wasn’t even hot. Mostly just warm. Night and day difference. Our temperatures are about 55To 65° today.
At lunch, I took it for another 15 minute drive and pick up some fast food which had the engine run in idle for maybe five minutes at the most. Did not run the heater or AC this time. Got home and it’s incredible how hot the engine gets without the heater running. I knew it would make some difference but I’m amazed at how great the difference is.. But then again, when I look at how Infiniti seals the air tight on that engine all around, I guess I shouldn’t be surprised it gets so hot.
.I tightened up the screw that holds that tiny tube on close to the thermostat cap. I have not seen any new leaks of coolant and the smell is definitely almost gone.
so what would you suggest next?

 

When you say it's getting hot does that mean the temp gauge is rising higher than the middle mark?

I think you need to pressure test your CAP and RADIATOR. Probably a small leak that's causing the system to not build pressure. It needs to build pressure to lower the boiling point of the coolant.

 

Here’s a little more detail. And thanks again for your help.
I took it for a drive today without traffic. 20 minute ride, maximum speed 45, didn’t use AC or heater. Temperature outside is 60°. When I got home, I put it in park and in about one minute later both fans kicked on and ran for about a minute. They kicked off and then started up again after another minute. The temperature gage inside the car stays at medium but the cover of the engine under the hood is so hot, I can barely touch it. Haven’t seen any new leaks since I cleaned everything off around the coolant area , and the Nissan dealership swears they did a pressure test when they put the two new fans in.
Maybe this is all normal but I just don’t remember these fans kicking on so often, especially in cooler temperatures outside. And I still smell a little bit of coolant but hopefully that’s just some left over from when the fans quit in the car spit Out cooling while overheating.

 

If you smell coolant then something is leaking, pressure test the coolant system AND THE CAP.

Coolant can come out as a steam, especially if the system isn't holding pressure. Water boils at 212 F at sea level, at 2000' the boiling point drops to 208 F. That's the temp of your engine coolant if the system isn't 100% sealed up and holding pressure.

The boiling temp when it's under 10psi of pressure is increased to 240 F at sea level, that's the entire reason WHY the cooling system is a sealed/pressurized system, it's just like a pressure cooker, raises the boiling point of water.

I greatly suspect you still have something leaking and not holding pressure, thus the smell of coolant (escaping as a gas) but not actually dripping coolant.

 

Also, a coolant pressure tester is EXTREMELY easy to use, first you test the radiator cap, there will be a PSI or BAR or kPA or kg/cm2 rating on the cap. Install the cap onto the tester and pump it up to make sure it holds pressure up to the rating on the cap, the G35 cap should hold 11-14 psi.

Next hook the tester up to the radiator and pump it up to the corresponding COLORED ARROW that your cap rating shows which is usually like 1psi higher than the maximum rating of the cap. Let the radiator sit under pressure for 5+ minutes and make sure it's not bleeding off pressure, if it doesn't hold pressure then listen around for the hissing sound, or look for air bubbling out with little bits of coolant somewhere, or look for coolant dripping from a fitting.

The most likely culprit is either the cap itself not holding pressure, or the radiator itself where the upper/lower sections are crimped onto the radiator fin assembly (entire length of the upper/lower part of the radiator).