Overflow tank bubbling

[Reichert]

I'm still new to my car ('90) and just finished a bunch of preventative maintenance, including flushing and filling the radiator (about 50/50 mix). I've been driving it around today, running errands in stop and go traffic. Coolant temp is topping out at 230 F (using the climate control readout). When I shut the car off, the coolant surges into the overflow tank, bubbling/churning for a few minutes as the engine is cooling down. Very audible outside the car.

This might be normal, but I'm not sure :) Also, the max temp seems a tad high, reading other threads about coolant temps, but the fans are running and the temp doesn't seem to be running away into dangerous territory.

Anything to worry about?

[RussMcB]

My initial guess - The radiator has never been out and has a ton of dirt in it. Search and you'll find lots of owners have taken their radiators out, often to replace with a new four core radiator, and found lots of years of dirt and leaves in there. Apparently, that stuff can get in but not out.

[cp1joel]

G'day there,

I have had this exact same problem a few weeks back when I took the Z for a drive. It was a very hot day here in aus (about 95F).

Car was running very hot, and once turned off the coolant in the reservoir was bubbling and then heard bubbling in the high fill engine reservoir.

According to Marc, he suggested to check the radiator for debris and also check for a worn out thermostat.

Could also possibly the radiator cap not holding pressure.

Hope this helps, have not had a chance to address mine but will keep an eye on this

[Reichert]

I suppose the radiator could be a little dirty, but the car has barely 20k miles on it - most of it driven in it's first few years of life. I took a quick look at the radiator and there aren't any major obstructions visible, and no bent fins. I also just replaced the thermostat with all of the other service work.

cp1joel keep me posted if/when you diagnose your own situation.

Also, when you said "aus" I thought "Austin" which is where I am but clearly you are on the other side of the world :)

[cp1joel]

Interesting !

Yep, on the other side of the world unfortunately.

Will keep you posted Reichert on anything I discover.

[Ccmano]

From what I remember your car has about 20k miles on it and you used the Haibeck method to refill the coolant. 230’ is a bit on the high side especially if ambient temps are not excessive.

I would first do another coolant system burp attempt. Let it cool overnight. Use one of the Haibeck methods. I use the one where you jack up the passenger side and fill. See if it burps any air that way.

Given the low miles, radiator fouling is less likely. But not impossible since you don’t know how it was used. More likely is that the thermostat is not fully opening. This is simply a function of age and well documented my Haibeck.

I had all the above on my last Z with only 48k miles on it. I ended up with a new thermostat and a new radiator. The radiator was clogged with sand in the fins.
H
:cheers:

[phrogs]

Did you burp the system

[Reichert]

I just went out and poked around the engine .. noticed the radiator cap was not screwed on fully, about a 1/4 turn short.

I didn't burp it on purpose, per say, but I did let it run and circulate while topping off with water the other day when I filled it back up.

[Ccmano]

I just went out and poked around the engine .. noticed the radiator cap was not screwed on fully, about a 1/4 turn short.

I didn't burp it on purpose, per say, but I did let it run and circulate while topping off with water the other day when I filled it back up.

Let it cool, jack up the passenger side as high as possible with the cap off. Let it burp and slowly add coolant until it stops burping.
H
:cheers:

[TX '90 ZR1]

If you still have the original cap on your fill tank(or even if not original) get it tested. On my '90 I found the pressure it would hold was considerably lower than it should be. This is probably more a function of age than miles. Mine has 34K.
I think the original spec on the cap is 17 lbs, but a couple of the members here recommended a 15 lb cap so I went with that.
These systems are getting some age on them & don't want to push the system!

[GOLDCYLON]

Replace the radiator cap.

[Reichert]

I did the burp procedure (lifting the passenger side as high as possible with the cap off.) It didn't produce any bubbles as far as I could tell, and I did not need to add any water. So I replaced the cap (this time correctly) and drove it around quite a bit today. Max temp was 104 (220F) briefly. No overflow tank bubbling today. Seems better. I went ahead and ordered a new thermostat as suggested.