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Discussion Starter · #1 · (Edited)
Hello all
Just looking for confirmation diagnosis please.

I have JDM 2003 Automatic, Base model, 350z VQ35DE stock with 150000km on the clock.

My first indication I noticed my thermo fan coming on, on a cool day. Second indication happened a few moments later with blown radiator top tank spewing steam and hot water everywhere. Temp gauge was normal up until that point then shot up of course.

I got her home and ordered a new radiator thinking that was the problem. Installed new radiator. After bleeding air and still overheating I then suspected thermostat.
I pulled the housing and the thermostat looks newish, I've had the car just on 3 years. I reinstalled the old thermostat and tried a re-bleed. (on an incline, using home made no spill funnel) I didn't really notice any big air burps though.

Here is where I get confused.
My temp gauge says normal, but I put a OBD bluetooth scanner and it reads engine coolant temp slowly rising to 101 degrees celsius (212F)
Both top and bottom radiator hoses are now more or less equal in temp (before I thought the bottom hose was cold but must have be mistaken)

My heater is blowing only cold air :(
switch from cold to hot to cold to hot...nothing...just cold.

So now I'm thinking water pump? Any thoughts please? ideas suggestions?
I did not notice any coolant leaking recently from weep hole (i look habitually on ground after moving my car), no codes other than low voltage on a knock sensor (it has always had that, after clearing it comes right back) no other indication of a water pump malfunction.

Thank you

ps I live in Japan

EDIT: Just pulled thermostat again and put it into boiling water. It does open but its a very small opening. Most other tstats I've checked this way I'm sure had a bigger mouth.
 

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Discussion Starter · #3 · (Edited)
Hi @dkmura Thank you for the reply.

It's not a real lisle funnel, just clear plastic water bottle with end cut off and some electrical tape to make it fit snug in the top fill spout.
Yes the replacement radiator did come with a new cap which was on.

I have ordered a new thermostat and a real Lisle funnel, will be here in a few days. In meantime I pulled the spring from the old tstat and jammed it partially open (will use it as a flow restrictor) and test again tomorrow. I want to know if this is a water pump failure or not. I'm REALLY hoping its not, but at 150000km its about due a timing chain replacement :(


I guess I will get plenty of practice bleeding this thing.
 

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Discussion Starter · #4 ·
@dkmura
Hello, looks like you are right!!

I put the old tsat minus spring in as a test and ran her up. This time there was definately burping and heater got warm (after a long time warming up). Thermofans kicked in at 95c and lowered temp back to 90c.

So it looks like just a bad thermostat after all. Man I am relieved, I didn't want the water pump issue right now.
 

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Hello all
Just looking for confirmation diagnosis please.

I have JDM 2003 Automatic, Base model, 350z VQ35DE stock with 150000km on the clock.

My first indication I noticed my thermo fan coming on, on a cool day. Second indication happened a few moments later with blown radiator top tank spewing steam and hot water everywhere. Temp gauge was normal up until that point then shot up of course.

I got her home and ordered a new radiator thinking that was the problem. Installed new radiator. After bleeding air and still overheating I then suspected thermostat.
I pulled the housing and the thermostat looks newish, I've had the car just on 3 years. I reinstalled the old thermostat and tried a re-bleed. (on an incline, using home made no spill funnel) I didn't really notice any big air burps though.

Here is where I get confused.
My temp gauge says normal, but I put a OBD bluetooth scanner and it reads engine coolant temp slowly rising to 101 degrees celsius (212F)
Both top and bottom radiator hoses are now more or less equal in temp (before I thought the bottom hose was cold but must have be mistaken)

My heater is blowing only cold air :(
switch from cold to hot to cold to hot...nothing...just cold.

So now I'm thinking water pump? Any thoughts please? ideas suggestions?
I did not notice any coolant leaking recently from weep hole (i look habitually on ground after moving my car), no codes other than low voltage on a knock sensor (it has always had that, after clearing it comes right back) no other indication of a water pump malfunction.

Thank you

ps I live in Japan

EDIT: Just pulled thermostat again and put it into boiling water. It does open but its a very small opening. Most other tstats I've checked this way I'm sure had a bigger mouth.
Thermostat stuck, replace it. Use 100% antifreeze, no water, be sure to get air out of system.
 
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