Hey guys...

I've been having some probs with my z...

Here's the thing.. it over heats, but not all the time.. it's kinda of weird.. it starts to overheat, so i turn the heater on get the temp to go down, or shut it off and let it cool.. i took it to a shop, guy looked at it bleeded the air out.. car ran fine for a week.. after a 200 mile trip it start overheating again.. took it to that shop, he checked, said it looked like the thermostat was messed up.. so we ended up jsut taking it out..

now it seems that the car only overheats when i'm going over 70-80.. then i turn the heater on the temp goes down and i kidna regulate it that way..

any of you have any ideas?
the thing is that if i take it to the dealership i'll end up wasting a lot of money.. the car has been salvaged (damage only to the back) so i get no warranty coverage at the dealership.. even tho there are only 11k miles on it..

i guess i might have to look for a good body shop around here.. but good specialists at reasonable prices are soooo hard to come buy...

anway.. if you got any ides/suggestions, i'd appreciate..

thanks

 

it def sounds like thermostat/water pump isssues, so this car was wrecked and has a salvage title?


oh also make sure that your fans work, had a similar prob with my stealth which turned out to be a broken engine fan.

 

yea i'm 95% sure that fans work... and yes this car has been messed up in the back.. not too much damage (but i guess enough to be declared slavaged) like i said it was in the back (which was completely changed with a new one)

how serious are theromstat/water pump problems.. i mean in terms of cost of the repairs?

 

ok heres how to see if your fan works, start the car and turn on your ac/heater the fan should turn on automatically, otherwise it usually turns on when a certain criteria is met. if its the thermostat part would be ~100 and diy, the water pump might be ~<200 and diy but more difficult than the thermostat but i dont know for sure how hard it would be without looking at it.

 

Well, replace the thermostat and check for fan operation at idle...after a few moments idling @ operating temps they should kick on.

 

you shouldnt need to replace the thermostat. but first make sure your fans work

 

did you physicly see the car when it was damaged?

off hand, it sounds like you got scammed.

yeah shes a beauty, little dent in the back, just happened to cost more to fix than the ~25k insurance value on her.

unless you saw the damage for yourself, I think somebody lied. good luck, no doubt this is the first of many many problems your likely to face down the road. and also no doubt it is related to the accident. seeing how this is the first time Ive ever heard this happen.

 

It is doubtful that you have a "fan" issue if overheating occurs at 70mph, the Fans do little at that speed, since airflow over the radiator is plenty at that speed so fans should be off until you slow down and "soak".

Could be a thermostat but also could be a head gasket leak.
If you had a leaky head gasket , one sure sign is if you radiator hoses "swell up" after a highway run. The swelling can occur if the Compression leaks and create compress air pockets in the water jacket. If thre engine was ever severly overheated chances are that the head warped and blew the head gasket(s).

Or on the bright side you could just have a minor un-evacuated bubble in the water jacket that simply needs to be purged.

 

Just curious...how would a dealership know it was salvaged?

Would any of them bother to do a title/vin search or to even look at your registration?

--mike

 

These VQ's can be sticklers for air in the system.
Def warm up the car and crack the vavle in the back of the engine bay to get out any excess air pockets. Might have to do it a couple of times and make sure the reserve tank is filled to the Max level.
The valve is a little black cap on the rear passenger side on the water line.

 

I had air in my system and it would only overheat when I reached a certain RPM. To bleed the air out just let the car cool down and open the radiator cap and it should release any air. Then refill with water. There is also a valve in the back water pipe that you can open to release the air. Its on the passenger side, just follow the radiator hose. You might have to do it several times. It took me several times to get all the air out.

How did you remove the thermostat? The thermostat is enbedded in a housing. Also, if you had no thermostat you water temp would barely rise.

 

ok guys.. thanks for the many repsponces..
i was working for a couple days and couldnt check the board..

i actually had the car dropped off at the place where i got it, the guys had it for like 2 days and said they "drove the hell out of it" going 70-80 on the freeway, abrupt stops and all .. anything that would get the engine going.. yet it didnt overheat..

well thinking that it might have been some air bubble that simply passed i took it back... on the way home.. after driving for like 30 min.. when i hit somewhere between 80-100, the temperature starts rising pretty fast.. not very surprised i turned the heater on, after a couple seconds of it running the temperature gauge went down (so now it's at exactly half of the meter).... so yea.. the problem keeps comming back after that.. whenever i go over 70-80.. i still havent had the car taken to the dealership...with this prob.

oh.. yes the car was salvaged, and the people i got it from do good business and actually take a lot of Zs that were hit in the backi think i could actually say that i trust them..

about the dealer finding out that it's salvaged.. they have to do it for every car they take in, especially when somebody is trying to use the warranty coverage..

the thermostat was removed by a friend who has a body shop, he bled the air a couple times, but cant really tell me what the problem is tho..

so yea.. i guess i'll be dropping it off at nissan some time soon

 

oh and yea... thermostat is jsut sitting in my glove compartment right now, still no help.. i'll check the fans again today..

 

Warm the car up and crack the air rlief vavle. Sorry the pic is a little dark.....but its back there on the water line. This willl get out what the radiator doesnt get out.

 

There's been many good suggestions so far. I'll add my 2 cents.

1) Blocked radiator air flow.
2) Dirty cooling system.
3) Faulty thermostat.
4) Faulty water pump.
5) Loose drive belt.
6) Coolant flow rate too high. Without T-Stat coolant "residence time" in the radiator at higher rpms/speeds is insufficient for proper coolant to air heat exchange.
7) Air in system. (Procedure 7a & 7b from recent how I did it experences.)
7a) Initial fill cold. Remove vent plug and very slowly fill the system. When liquid level is seen in vent plug hole, replace plug. Finish filling radiator and replace cap. Fill surge tank to maximum level line.
7b) Start engine and warm to normal coolant temp. Set heater temp at 90F, idle minimum of 2 minutes, rev and hold rpms at 3000k for 20-30 seconds, idle 10 seconds, repeat two or three times, shutdown and cool. Check surge tank often and keep at max level. Don't allow surge tank to go empty.
Note: It can take several cycles/days to completely evacuate all air from system. During this time set temp to 90F just before shutting off engine at night and back to normal setting after starting cold in the morning. Refill surge tank to max level line when cold. When surge tank level stablizes all entrained air should be gone.

DaveO

 

This DEFINATELY smells like air in the cooling system. The same thing happen to me when I drained the coolant for the Greddy kit. We filled it up totally, and it appeared to be full. Drove it around the block and the temp guage starting acting erratic....hot...cold...hot...cold...etc.

Ended up there were massive amounts of air in the system. We cleared it with the release valve mentioned, and one of those radiator plunging thingys.

Since this car was salvaged, it was very likely that the coolant was not replaced correctly when they reassembled everything. The 350Z is VERY difficult to flush and refill coolant. Most mechanics will mess up this job.....it takes a lot of patients....

 

Sounds like it could be some air dams or air seals between the radiator and the a/c condenser. If these seals are missing it will cause the air at speed to take the path of least resistance which will be around the radiator and or over or under the car. Make sure the splash pan is in place!!!!!! The air will go thru the opening and then just under the car at speed!!! If not then I bet that is the culprit of your problem.

Let me ask you a couple of questions? Does it overheat any other time or just when you are at speed? If just at speed then most likely it is one of the problems I described above. Air pockets will generally keep the heater from working too. So if the heat works fine (not intermittently) then most likely it's not an air pocket. Idle the car and get it up to temp and if the heat works at idle then most likely an air pocket is not your problem. Also air will do as gq model said the temp guage will be erratic jumpin from hot to cold up and down.

Oh, and btw put that thermostat back in. Your car will not go into closed loop without the thermostat. Gas mileage and other things like emissions can't be controlled when the car is not at operating temperature. Poor idle and generally rough running can be present also without a thermostat.

I hope that you have not overheated the car into the red zone on the temp guage. If so the probability of a blown head gasket is very likely. The VQ is all aluminum and very unforgiving as far as overheating even probably more so than an engine with just aluminum heads.

Good luck and I hope this helps. If this don't help try to give me some more detailed info and I will do what I can. I work on cooling systems for a living and will help you out all I can.

Tony

 

I have no expertise to add here--but it sure is great to see fellow VQ owners willing to help another forum member out. I'm learning a lot from reading this board.

--Steve

 

I cant imagine modding a car wihtout the internet forums.

 

I can't imagine modding a car without a LAPTOP in the GARAGE!