andy-gts

the only potential piece that could fall apart and block a passage is what........t stat (doubt) but shouldnt you pull the stat and throw a new one in after checking the old one....sure sounds like some passage is plugged. could the hoses to and from the overflow tank be faulty and plugged...

hacker-pschorr

No such thing as "excessive boost", it's all in the tuning.
You can blow a head gasket at 1psi if the tune isn't right. The air / fuel is only one piece of that puzzle.
78-86 cars do not have knock sensors to save you from an iffy tune.

It could also be an old, ready to fail head-gasket and the now increased cylinder pressure is putting it over the edge.

j.kenzie@sbcglobal.net

Checking the thermostat sounds good. It's pretty new but isn't there good way to check it with IR gun? I will double check all hoses but the car has been running normally for a few months at least with no known changes.
Thanks
Dave

j.kenzie@sbcglobal.net

I ordered a head gasket leak test kit.
Dave

j.kenzie@sbcglobal.net

Hello again,
I came home from work and topped up my coolant reservoir about 1.5 more liters. I then put on my 7PSI cap, and started up the car in my garage. There is a box fan in front but not much cooling air although OAT is only 74 degrees. The car gradually heated up to about halfway between the 1st and 2nd lines on the temp gauge. My upper hose was reading 198 by IR. Thermostat opened about 140. Radiator showed inlet temp of 145 and outlet side 93 degrees. Coolant temp gauge in car gradually crept to about 3/4 of the way to the second white line and my temp warning light came on. Temp was holding there so I let in run another minute or so. Suddenly my temp gauge dropped to the first white line and my low coolant warning light went on. My upper hose went soft (sorry). Temps dropped by about 20 degrees all around except radiator less so.
I think that was a big air bubble. It may not be the last, but I feel so much better after that burp.
I am going to let the car cool down completely, and refill with more coolant. I will repeat the heating cycle tomorrow, but I am hopeful that air lock may have been the problem.
Thanks for reading,
Dave

soontobered84

I like that line of thinking!

Randy V

It sounds like you are on the right track.

j.kenzie@sbcglobal.net

Thanks all,
I have to say my initial cooling system filling technique was pretty poor. After fitting new radiator, after unknown but significant coolant loss, I refilled only via the coolant reservoir. I kept topping up as the engine ran, and I thought is was pretty full so I initially took it for a short local drive. That's when it overheated. I thought airflow would help, but I was wrong.
With the SC in place it's not so easy to get to the upper hose connection to the water housing, so my fill points are pretty limited.
Anyway, I think I probably caused this air lock problem myself by poor technique. Hopefully my heat cycle/refill/burp method with eventually succeed.
Thanks for the help,
Dave

j.kenzie@sbcglobal.net

Hi again,
2.5 liters more coolant added to system. This time it held a steady-state temp just above the first white line. No high temp warning light, and all in a garage with poor airflow. I am beginning to think I am on the right rack, too. I will check again tomorrow and maybe take it out on the road. The fact that I have poor heat from my vents, makes me think there is still air in at least the heater core, and maybe elsewhere.
Thanks,
Dave

chitown928s4

If you get her buttoned up bring her to Sharks in the Mississippi this weekend to strecth her legs out.

19psi

I'd throw that original cap in the trash. If it's stuck, that may be what blew out the tank. Then your problems continued with trapped air because it wouldn't release at the rated pressure. With your other cap on, things seem to be going back to normal.

Had something similar happen to me with another car long ago. Original radiator leaked, it was old and I didn't look it over or think much of it. Bought a new one and the first time out it started leaking. The core was ballooned out from excessive pressure. I have a radiator pressure tester with a cap adapter which I should have used beforehand. The cap maxed the gauge out and never did release.

Mrmerlin

FWIW here is a fill procedure for the 928 it works on every year,

The 928 cooling system is self bleeding.

To fill it ,
open the heater control temperature controller full hot,

add about 4 gallons of coolant via the coolant bottle,
this may take a while as the system will bleed off the air. (note engine off)

Once your at close to 4 gallons installed, start the engine.
Let the system come up to temperature coolant cap off.

Once the fans come on, or if no elex fan after the thermostat opens, install the cap.
NOTE coolant bottle should be filled just over halfway.

take the car for a drive about 5 miles, this will fill and purge the air from the heater core.
park the car , shut off the engine let the car cool off .

Once the car is cool then remove the cap and top up as necessary,
coolant level cold should be just over the seam in the bottle,

NOTE The tank splitting would indicate a system overpressure,
use the block tester to see if you have hydrocarbon escaping via the coolant system.
Use the 100 cap a new one.
make sure you have a good coolant bottle, a good heater control valve and short hose.
Check the timing belt tension cold and at TDC.

NOTE if the belt is loose then you may have a migrating bearing in your water pump

j.kenzie@sbcglobal.net

Thanks all.
Stan, I will check for HC in the coolant this weekend. New heater valve, and short hose. Timing belt seems fine. Tight and centered. 1 year new Lasso WP and Prksnr. I tried to fill kind of like you said, but I think I was impatient in letting the system self burp. I will stick with my 7PSI cap for now althoug the 100 cap worked fine for quite a while.
Thanks,
Dave

linderpat

The cap off part of this process is critical - it is how the self bleeding system works. If you fill and drive without first running to temp with the cap off, you could have problems, and maybe that is what happened here.

Mrmerlin

^^^^ what Ed said !