Can someone help me solve my mystery?

When I got my 2003.0 G35 Sedan back in March, I noticed the coolant reservoir was empty and the cap was missing. The dealer wanted me to drive back and pick up the cap but instead I decided to buy a replacement OEM cap from Napa.

I added some 50/50 coolant to the reservoir max line and left it alone.

Car drove like normal since it was cold outside but on warmer (60*F+ days) the fan clutch would sound loud like a school bus once the car warmed up to normal temps and would stay running 100% no matter the speed. Coming from 3 past 2005 G35s w/electric cooling fans I found this to quite a shock and something I want to resolve.

You all have noticed I've made a couple threads re: fan clutch and I've definitely taken everything shared into consideration.

This past week, I decided to do an experiment.

Here goes:

I've noticed the fan doesn't always come on until the car's warmed up.

When it does come on it's loud like a tornado and does not tone down.
At this point, I hear more fan noise vs the engine/intake etc.

After searching through threads, I've found 2 consistent explanations.

1. The fan should come on for a few mins during cold start and then quiet down (mine does this)

2. The fan shouldn't always stay engaged 100% like it's stuck open unless the engine is running hot (mine doesn't fully engage until the car's warm & temp gauge always heats to the middle and stays there )

What bothers me while researching older threads (10-14 years old etc) is I've seen what would have been newer 03 sedan owners mention their fan never came on or if it did, it was quick and went away when after driving over 20 mph.

That's what I want.
Not a diesel truck sounding fan when it warms up but as close to a normal sounding G35 as possible.

When my fan comes on, it stays on all throughout the RPM and speed range.
The other day it was 40*...I got on the highway and the fan was still loud even while I accelerated at 70mph.

I thought its supposed to disengage and quiet after 20mph. (Mine didn't)

Someone correct me if I'm wrong but I don't think that's normal.
I recently started questioning if my car was running hotter than it should which is making the fan clutch stay engaged.

Did some digging through the records and noticed the previous owner took it to Sears back in 2018 and got a coolant flush.
I also noticed the radiator cap looks new and is OEM Nissan.

Started asking myself....could it be Sears put a wrong type of coolant in the car making it run hotter than it should?

This past week I:

A. Picked up some VP Racing Cool Down additive to see if that would lower coolant temps.
B. Bought a Bluetooth OBD2 reader and Torq App to monitor my coolant temps while driving to really see whats going on.

Unfortunately I did not get a before Cool Down temp measurement(Still kicking myself)
Here's the results from my experiment and where I need your expertise:

Ambient temp of 72F*

I did notice right away that I can drive a few extra mins before the fan engaged to the loud zone.
I WISH I got the coolant temps before so I can compare but based on what you guys know, are these normal temps for 1st gen stock G35s?

Here's the results:

Let car warm up 20 mins after adding Cool Down.
Before driving car heated up to upper 170s*

While driving:

Car stayed around 183-185* for 5 mins or so cruising around. No loud fan yet... Just normal quiet stock G35 engine sound until the temps reached 186*. That's when the fan clutch started it's noise like a diesel fan.

That day, the car stayed in a temp range of 192-195.6*F including a lot of stop and go driving. It hit 203* then shot down to 199* while idling at the local Portillos drive through for almost 10 mins etc. (Had A/C on too)

1. Is this what you 03 G35 owners consider as standard coolant temps for a healthy cooling system?
2. Based on what you hear, is the fan clutch working normally or should I go ahead and replace it?

What else should I look for/consider?

Thanks for taking time to read this and offering any insight you have to help me tackle this cooling situation


- Michael

 

I'm 04.5, and I run a Scangauge to monitor temps and other vitals. My electric fans come on at 204*, and the fans turn off around 19--195* I believe.
I have the 6mt thermostat. 6mt = 169*, 5AT = 177*. Z1 only stocks the 6mt one. I didn't know they were different for 5at vs 6mt until after I installed it with a new radiator and hoses and my car was running 8-10* cooler!!!
I didn't know for certain they were different until I checked the FSM:

I don't know what the spec is on the 2003's with Mech fan.

My car warms up to about 175 and hovers around 185-190 on the freeway and around town. Hotter if the ambient temps are higher. The highest I ever see my coolant temps get to is about 206-208, and that's when I am pushing it in canyons or its 100*+ outside and I'm in traffic.
If your water temp was getting above 210*, then I would be concerned, but not worried.
I would replace the fan clutch, as it sounds like you have a little anxiety about. If the part is original to the car, its 17 or so years old, and it wouldn't hurt to have some peace of mind.

 

Thank you Andrew for taking time to read through my long post and share your insights.

Thank you Cleric for your advice in the other thread I had re: the fan clutch.

I think I will replace the fan clutch anyway due to age etc. The radiator, hoses and thermostat seem to be operating fine for now but I know those will need to be replaced at some point in the future due to age as well.

At 132k, just want to keep my eye on everything and stay on top of maintenance

Thank for sharing the thermostat info as well. Had no idea they replaced it with a different model as well.

Almost seems like an upgrade if I'm reading your post correctly

 

Let us know if you make any progress!
Yeah, I ended up with the 6mt thermostat more by mistake, as its the only OE thermostat Z1 stocks. I bought it with other parts I needed (rad and heaters hoses) thinking it was the same as I removed, then I started checking part numbers when I noticed it was running cooler. Thats when I found that there was two OEM p/n's for the cars, and the FSM confirmed they are diff temps. I think of it as a happy accident, as my fans were coming on all the time with the original thermostat, radiator, hoses, etc. which concerned me a little. Now they only come on once in a while.
If you end up replacing the thermostat, I'd pick up the Z1 aluminum bleeder. The stock ones are plastic and prone to cracking/breaking due to age or even trying to open them. Pricey, but its $32 well spent.
https://www.z1motorsports.com/z1-pro...e-p-11190.html

 

Thank you Andrew.
I will keep that in mind when I pickup my clutch and thermostat.
THAT looks like peace of mind and is EXACTLY what I'm looking for.

I'll be sure to log the data in Torque and see how it compares to what I have now