topping off/bleeding coolant system

[Mike Christian]

I have a SPF with 351 based 427. I had some coolant leaks behind the bulkhead that lost about a quart to half gallon of coolant. Now a few months later, I need to move the car from the hangar to my new workspace. I started up the car to run it (without topping off teh coolant), and the water temp gauge started to read high after just a few minutes at idle. I could touch the main coolant tubes and they were not hot. I suspect I have air in the system and the sender is affected.

Anyway, I am looking for suggestions on a topping off/bleeding method that would get this car out of the hangar and home.

Thanks,
Mike

 

[Seymour Snerd]

I am looking for suggestions on a topping off/bleeding method that would get this car out of the hangar and home.

Fill the header tank to the top, then jack the front as high as you can, let it sit for a couple minutes, lower it, jack the rear as high as you can. Any gurgling you hear represents progress.

 

[Mike Christian]

Will give that a try, thanks!

 

[Tim Kay]

I typically do as Alan outlined above but just the other day I borrowed a 'cooling system pressure tester' and it worked fantastic. I filled and flushed my system three times in 2 hours and not once did I get trapped air.

With the system empty I filled the system via the reservior tank, once full I attached the pressure tester to the reservior and open the petcocks allowing the pressure to move the coolant through the system. Two to three cycles and the system was purged and full. I then start the motor and let it warm up to circulate then cool down and on last 'burp' at the petcocks. done

Usually I have to warm up the coolant, raise the front end, let it cool, 'burp' the lines and repeat a couple times then let it sit over night and repeat the procedure one more time if I'm lucky.

I have a petcock on the top of the radiator and another petcock on the top water tube coming off the manifold\thermostat (highest point of the system). The petcock on the water tube probably contributes best to 'burping' the air out and I highly recommend it. I didn't always have that one but once I did it helped the procedure quite a bit.

 

[Mike Christian]

Any thoughts on driving the car 20 miles to get it to my workshop to bleed it there? Is that safe or stupid?

 

[Seymour Snerd]

Any thoughts on driving the car 20 miles to get it to my workshop to bleed it there? Is that safe or stupid?

That's an interesting question. In theory the system should bleed itself since it has bleed lines at all the high points. So I think it would be worth a try as follows: drive around locally all the while accelerating and decelerating as hard as possible, since that "sloshing" will agigate the system and (my theory goes) cause any air to find its way to the bleed lines. If you can get the temp reading to stabilize at the thermostat temperature while cruising, you're done.

One thing that intrigues me about Tim's post is that I found the same thing by accident. I was using a pressure tester to expose leaks, and noticed that if I filled the system right to the top, pressurized it to say 15 psi, and left it over night, the next morning when I opened the cap and depressurised, there would be all this gurgling and the header tank level would drop. After a few cycles I could pressurise the system with hardly any pumping, i.e it was "hydraulic locked" which demonstrated there was no air in the system. But I never have understood why that works. Maybe the pressurizing is irrelevant and the same thing would have happened just by letting the full system sit, but if so why does it wait for me to depressurise before it gurgles?

 

[Tim Kay]

Mike,
As long as you have an accurate temp reading you'll know right away if there is any air in the system during the first heat cycle. Once the temp reaches the point the thermostat opens and it continues to rise it only takes a couple minutes before you see it get beyond normal. I would first drive it locally like Alan suggest.

Alan,
My guess is once the pressure is reduced it allows movement in the coolant allowing the trapped air to get by just like when the coolant gets hot and expands creating pressure then contracts when cooling thus the 'gurgling' starts.

In my opinion, the theory with the pressure tester allows the coolant to push the air through the system and out the petcocks. The beauty is it's all done while the motor is cold and you're not subject to working around the piping hot coolant as you are when burping the system after it heats up.

Somthing you need to be concerned with when using the pressure tester is to make sure either the thermostat is removed or you have some kind of bypass that allows fluid\air by the thermostat. Also, it doesn't take much pressure at all, 9-10 psi was sufficient for me.

 

[Cliff Beer]

Fill the header tank to the top, then jack the front as high as you can, let it sit for a couple minutes, lower it, jack the rear as high as you can. Any gurgling you hear represents progress.

Ditto what Alan said. You can also use a hill if you have a steep one near you. I have a 25 degree hill near me that gets regular "bleeding" use....

 

[Mike Christian]

I first realized I had a problem when the temp gauge went high way too fast. I think it might be in a bubble. Therefore, I am not sure how accurate my temp will be. Where is the temp sensor located? I guess I will top off and try the techniques suggest (without the pressure tester as I have none). If it stabilizes, tehn I will drive it home and take care of some things there.

Thanks!

 

[Tim Kay]

Your temp gauge is more than likely fine. Since it rose so fast it definitly indicates a blockage. Once it starts to warm up the temp rises quickly if the coolant isn't circulating. Raise the front end (easily done on an incline driveway, street, hill ect as mentioned above) let it cool down, crack the pressure relief cap and you should hear what Alan decribed as 'gurgling'. It may take a couple heat cycles.

 

[Mike Christian]

I will try it!

 

[DaveM]

I first realized I had a problem when the temp gauge went high way too fast. I think it might be in a bubble. Therefore, I am not sure how accurate my temp will be. Where is the temp sensor located?
Thanks!

I believe you have a Roush engine too Mike? The water temp sensor is right behind the thermostat housing in the intake manifold.

 

[Seymour Snerd]

I believe you have a Roush engine too Mike? The water temp sensor is right behind the thermostat housing in the intake manifold.

If the temp sensor happens to be sitting in a bubble you get super-fast rise in indicated temp. Alarming but possibly misleading. Iae just another reason to get the bubbles out.

 

[Seymour Snerd]

My guess is once the pressure is reduced it allows movement in the coolant allowing the trapped air to get by just like when the coolant gets hot and expands creating pressure then contracts when cooling thus the 'gurgling' starts.

Yours is the best explanation I have: if I pump it to 15 psi, that's double atmospheric and should make all the bubbles have as big. Then when I release the pressure the bubbles suddenly double in size, which agitates the water causing some of the bubbles to move to a place where they can rise up into the header tank and out. So maybe sitting overnight has nothing to do with it....

 

[Mike Christian]

Yes Roush 427. Topping it off and then driving it accelerating and decelerating got gurgles and got the temp gauge to settle down where it should...

Thanks!

 

[Seymour Snerd]

Yes Roush 427. Topping it off and then driving it accelerating and decelerating got gurgles and got the temp gauge to settle down where it should...

Thanks!

Cool! Maybe we should call that the official GT40s.com SPF cooling system bleed method: "go out and drive like hell!" :laugh:

 

[Mike Christian]

sounds good to me! I can put that in my bag of excuses when I get pulled over....

 

[Chuck]

I first realized I had a problem when the temp gauge went high way too fast. I think it might be in a bubble. Therefore, I am not sure how accurate my temp will be. Where is the temp sensor located? I guess I will top off and try the techniques suggest (without the pressure tester as I have none). If it stabilizes, tehn I will drive it home and take care of some things there.

Thanks!

Mike: Many car parts stores (Autozone, OReilly's, etc.) have free loan programs where you can use a pressure tester (and other tools) at no charge. I took advantage of that program to chase down a coolant leak a couple of years ago and it worked well.

 

[Mike Christian]

Good idea Chuck. I will see if there is one close to me or on the way from the airport and give that a try.

 

[Seymour Snerd]

Mike: Many car parts stores (Autozone, OReilly's, etc.) have free loan programs where you can use a pressure tester (and other tools) at no charge. I took advantage of that program to chase down a coolant leak a couple of years ago and it worked well.

I deliberately tested mine at 20 PSI (i.e. above cap pressure) overnight and in so doing found several leaks, mostly due to not having the hose clamps well-centered on the grooves in the tunnel pipes. Knowing that the system will hold 20 psi for long periods of time makes me a lot more confident I won't get stranded with hot water all over the place.