tveltman

I recently had a loss of coolant accident when the lower rad hose developed a hole and the car sprayed water all over the road. Flatbeded it back, got a new hose, accidentally poked a hole in the radiator. Pulled radiator (all aluminum) and had repaired at local shop, put back I , car took about 3.5 gallons of coolant. Now the needle on the temp guage climbs past normal temp up to the high white line. I shut it off and let it cool back down to normal operating temperature and tried again several times, but each time the needle would eventually rise. High water temp confirmed by temp II sensor, which goes into my aftermarket ECU.

Can anyone suggest an explanation for what is going wrong? Water pump is brand new engine guardian pump. Radiator cap is brand new also. Car ran cool as a cucumber before LOCA accident. TIA (and sorry for terseness, I'm on my phone)

Speedtoys

Air pocket in the system...or maybe the Tstat is cooked.

Is the radiator hot when the engine is?

If so, ALL of it?

Top hose & lower hose as well?


I do agree that the block gets hot..but...what else?

928 at last

I would make sure you've burped the system completely, and checked the coolant levels. Mine runs just a hair below the last white line normally, so unless you're "heading for the red" your reading wouldn't botherme.
What's it show on an IR gun? Upper and Lower hoses at full indicated temperature? You may have an air bubble or a new normal....the gauges aren't the most accurate at the best of times.....

dprantl

The factory says the 928 cooling system is self burping, but some 928's would disagree with it. My former '86 had problems and needed help getting all the air out of the system. My GT doesn't require this. YMMV.

Dan
'91 928GT S/C 475hp/460lb.ft

Jim M.

If the gauge is accurate the 2nd white line is 190 deg. F. The stock thermostat is 190 deg. F., so all is normal as long as it doesn't continue to climb into the red zone. How was the radiator repaired? Did they just solder/braze the hole shut? If so, you may have lost some circulation capacity. The 928 is self burping, try squeezing the upper hose while it warms up, you can feel the water surging as you squeeze.

tveltman

I just checked the thermostat. It opens in boiling water (although it took it longer to crack open than I thought it would, but open it did. I took it off the boil and measured the temperature while stirring the pot. It was fully closed by around 170 F, and upon slow reheating opened right around 180 F, which is just about 83 C, which is what the thermostat is stamped at. Unless you can get a "sticky" thermostat, then that is t the culprit. Also the radiator was hot to the touch while the car was running previously so I thought tstat unlikely.

Mrmerlin

Ok so do this,
fill the coolant bottle to 3/4 full ,
on a level surface
with the cap off and the heater opened to full hot,
run the car till the fans come on,
then put the cap on.
Take the car for a drive cover about 5 miles with the heater still full hot,
then park it.
let it cool and then check the coolant level.
Dont remove the cap till the system is cool.
once this is done your cooling system should be filled.
If you need to add more coolant then add some to just above the seam on the bottle.
put the cap back on and take it for a drive,
use the IR gun to check tempos of inlet and outlet of radiator hoses,
report back what you find,

tveltman

I checked this out last night. My diagnosis is the thermostat is somehow bad. The needle moves into the red zone, at which point I shut her down, and the upper radiator hose is under significant pressure, and looks like it is inflated. Around the upper inlet to the radiator, the radiator is hot, and this is originally why I thought the thermostat was working. However, the lower hose and most of the radiator is cold to the touch.

I think this must mean bad thermostat. Any other diagnoses before I call up Roger?

Mrmerlin

get a new thermostat rear seal
a new thermostat
and a new O ring also
consider replacing the heater control valve and short hose since the system is not full

tveltman

Control valve and hose are brand new. Less than 40 miles on them. Rear seal has less than 5000 miles on it, but I can replace it anyway.

Bill Ball

I don't see how this could be the T-stat. If the T-stat is stuck in the cold position, the water just circulates in a radiator bypass passage back to the block. The upper radiator hose would not get turgid. If it's stuck in the hot position, you get radiator flow all the time.

The symptoms are consistent with a blocked radiator or a failed water pump.

Mrmerlin

I am going for the easy stuff first,
since the engine was working properly prior to major fluid loss there is a chance the thermostat went bad , Next will be a waterpump

nc_growler

I've received some really good advice from folks on this board... Some of the best was this:

What was the last thing you did before you started having that problem... Go back and double check that.

Ian S4

I wonder if your radiator came with little plastic plugs in the holes, and you maybe forgot to remove one or two of 'em?

(Please don't ask how I came up with this suggestion...it's too embarrassing...)

tveltman

No plugs that are removable, i'm certain. I'll check the impeller function of the water pump. I'm suspecting its the pump. I ordered a new tstat anyway. Never hurts to be thorough. I'll have a better idea when I can have a look at it tomorrow.