1987 300ZX Wild Overheating Issue

[stewartmotorsport]

Recently replaced temp sensor, O2 sensor, plugs, wires, cap, rotor, etc. for smog. Passed with flying colors.

Recently driving, temperature gauge was fluctuating wildly. Super hot, then normal, then super hot, then normal.

Towed it home.

Replaced water pump, thermostat, timing belt, and tensioner.

Same symptoms: temperature gauge was fluctuating wildly. Super hot, then normal, then super hot, then normal.

Car was "burped" to make sure no air bubbles. No obstructions that we can see. Fresh coolant. Full flush.

Outside of the temperature issue, it runs great.

I am very confused.

Help?

[LunarShroud]

is it actually getting super hot, or could it just be the gauge malfunctioning? my friend's 240sx had a similar problem awhile back, but i can't recall what the actual problem was. ruling out air in the coolant systyem, it's an odd problem to say the least. also, is it digital or analog dash?

[evildky]

sounds like air in the system, when you "burped" the system, did you have the heat on high? and allowed the car to warm up first?

[evildky]

I merged and deleted your duplicate post

[stewartmotorsport]

Digital Dash and I considered that the gauge and/or sensor might be faulty, but that's not the case. It is hot and boiling over through the overflow.

One th9ing that concerns me is that the water flow (when viewing through the radiator cap/filler neck) seems to be kinda of slow. It flows, but I question the rate. I may remove the thermostat all together and see if that helps.

Burped it pretty good - heat on high...several minutes...will do it again though.

I am pretty sure the radiator is ok...I was able to flush it very easily...to the point where I got clear water coming out the bottom drain. I'm wondering now if I have a blockage somewhere internal. I don't see how that is possible, but nothing surprises me anymore.

Also going to replace the radiator cap.

[evildky]

when the radiator is the issue it generally keeps cool at idle and slow driving then gets hot at high speeds, when it's the thermostat it just keeps getting hotter the longer it's trunning and never cools down, when it fluctuates it's air in the system

[stewartmotorsport]

This is my son's car, and he tells me that the wild fluctuations seem to be at all speeds and conditions once the car is warmed up...however, he drives a lot of highway miles, so it may indeed be the radiator. But the water flow through it was very good, and I saw no leaks...that does not mean that there aren't any though.

I may replace it for good measure, and refill the whole system again.

[evildky]

a blown head gasket can introduce air to the system and cause radical temp swings and boiling over or exhausting through the overflow

[stewartmotorsport]

Agreed - and I have seen that before. But as of this moment, the head gasket is not blown. Smooth idle, no oil in water or vice versa. I have not done a compression check, but I have seen cars with blown head gaskets before, and they don't run well, no matter what you do to them. This car runs REALLY good.

I'm leaning towards more air in the system or a bad radiator.

[evildky]

if the car will idle all day long and never get hot it's not a HG or air in the system, if the high temps only present at speeds it's a radiator

I have seen cars run well with ablown hg, if it's just a small compression leak that goes into the coolant passage you won't find coolant in the oil or any other stmptome and a compression test won't indicate an issue either, but a leakdown test will show more loss in that cylinder and the coolant overflow will smell of exhaust fumes, the HG isn't a real typical problem on these engines as they have 13 headbolts per head! but it can still happen