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Old 01-05-2010, 09:43 PM
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How do I get rid of air lock in cooling system?

Ive got a pretty warm 408sbc in my 67 Holden, its running 10.4/1 comp and a decent cam, so it gets warm fairly quickly. There is a decent size alloy radiator and a 14" electric fan, im also running an electric water pump. It seems to sit around 170 degrees pretty easily once everything is working fine, but every time I drive it the temp goes up to about 230 on the gauge for a minute or so then drops just as fast back to 170. Ive got the sender unit for the temp gauge in the side of the cyl head between the rear two exhaust ports on my alloy AFR hreads, so I imagine its reading a bit on the hot side anyway. Could this be an air pocket, or is it just hitting max temp at that spot in the engine before the thermostat opens?
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Old 01-05-2010, 10:59 PM
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Don't worry about it, normal operation. Run it hot without the rad cap on until there are no more bubbles, thats it. Of course if you have some goofy rad setup that lower than the engine you could have an air lock problem, but what you describe is normal. Temps spike radically in the head, move the sensor into the intake manifold if seeing it scares you.
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Old 01-05-2010, 11:08 PM
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Quote:
Originally Posted by Holdon
Ive got a pretty warm 408sbc in my 67 Holden, its running 10.4/1 comp and a decent cam, so it gets warm fairly quickly. There is a decent size alloy radiator and a 14" electric fan, im also running an electric water pump. It seems to sit around 170 degrees pretty easily once everything is working fine, but every time I drive it the temp goes up to about 230 on the gauge for a minute or so then drops just as fast back to 170. Ive got the sender unit for the temp gauge in the side of the cyl head between the rear two exhaust ports on my alloy AFR hreads, so I imagine its reading a bit on the hot side anyway. Could this be an air pocket, or is it just hitting max temp at that spot in the engine before the thermostat opens?
Are you sure the thermostat is working right.. Did you check it..
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Old 01-05-2010, 11:25 PM
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Quote:
Originally Posted by NEW INTERIORS
Are you sure the thermostat is working right.. Did you check it..
Yes I checked it, if it wasnt working im pretty sure the temp wouldnt settle.
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Old 01-05-2010, 11:40 PM
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Can you let it sit at idle until it get's to 170 are better ?? (With the cap off) If so what happens then.. Does it try to push the water out.. If it does.. Try in keep filling the rad very very very slow.. That way you don't close the thermostat while your filling.. I had to do that on one of my big block's.. It will keep trying to push it out,, But keep filling slowly.. Very little at a time is the key.. It sound like you have air in it..
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Old 01-06-2010, 07:59 AM
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Another trick is to park on an incline with the front of the car to the up side... steeper the better. Remove the rad cap and run the motor, slowly filling with coolant. This should allow any air trapped in the block to burp out.
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Old 01-06-2010, 08:11 AM
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or you can just drill a 3/32 hole in your T-stat. warm up may take about 30 seconds longer but it solves the air lock problem. I drill a small hole in every T-stat I install just so there never is a problem.
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Old 01-06-2010, 08:28 AM
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Quote:
Originally Posted by Holdon
Yes I checked it, if it wasnt working im pretty sure the temp wouldnt settle.
This is not necessarily true. A thermostat can intermittently fail which will cause the temp to go up within a few seconds and then come right back down. Years ago I had a new Dodge with a 318 that had less than 400 miles on it do just that. An intermittent spike in temp and then back to normal. Did it several times over a week or so until I changed the thermostat and that solved the problem.

Whenever I build an engine now days I always install a thermostat that if it fails it will fail in the full open position. Much less chance of overheating that way.
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Old 01-06-2010, 08:35 AM
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Steam Holes

Hey Man, Did you drill the steam holes in the heads? Might have something to do with your issue. olnolan
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Old 01-06-2010, 09:11 AM
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Quote:
Originally Posted by Holdon
Ive got a pretty warm 408sbc in my 67 Holden, its running 10.4/1 comp and a decent cam, so it gets warm fairly quickly. There is a decent size alloy radiator and a 14" electric fan, im also running an electric water pump. It seems to sit around 170 degrees pretty easily once everything is working fine, but every time I drive it the temp goes up to about 230 on the gauge for a minute or so then drops just as fast back to 170. Ive got the sender unit for the temp gauge in the side of the cyl head between the rear two exhaust ports on my alloy AFR hreads, so I imagine its reading a bit on the hot side anyway. Could this be an air pocket, or is it just hitting max temp at that spot in the engine before the thermostat opens?
You're monitoring the hottest place in the engine, this will become very hot without coolant circulation especially compared to the more average coolant temp when it's monitored at the manifold return.

Since this is happening before the thermostat opens, it's likely the engine doesn't have internal circulation before the thermostat opens which is provided in two places with the SBC. The first is the transfer hole found on the right side of the block. This is often closed off by people who want to force all coolant thru the radiator. Closing this and the elimination of the heater bypass, will result in drastic local overheating around the exhaust valves when the thermostat is closed. In aluminum heads this leads to the hard seat insert coming loose and in cast iron heads cracking thru the exhaust seat. The second return is thru the heater system, typically a hose runs from the common coolant return of the intake manifold on the engine side of the thermostat. The hose goes to the heater core and returns coolant via another hose to the coolant pump intake. This provides coolant circulation when the thermostat is closed which again avoids the problems with local hot spots around the exhaust valves boiling the stagnant coolant and overheating specific places around the exhaust valves as previously described. At the minimum, a hose needs to connect the coolant return before the thermostat to the intake side of the coolant pump. If the pump isn't so provisioned, most modern radiators have fitting location on the pump intake tank, or a T fitting can be put into the lower radiator pump intake hose.

So many people get overly concerned about this bypass coolant getting around the radiator and they shut these bypass systems off. The OEM designed component cooling capacity around the presence of this necessary evil, if your installation is having problems with cruise cooling, the solution is a bigger radiator, a pump with more capacity, etc. not plugging the bypasses as so well proffered in the media by people who, however well intentioned, just haven't thought the entire problem through.

Bogie
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Old 01-06-2010, 09:19 AM
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When using an electric water pump, you have to remember that they only push so many GPM(gals per minute). With a motor making HP, the pump can usually keep up when at idle but at speeds the pump is still only pushing the same GPM as it does at idle. Electric water pumps usually work ok for the street but can't flow as much as a belt driven. The temps will fluctuate especially at speed, at low speed they should even out.
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Old 01-06-2010, 11:42 AM
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Quote:
Originally Posted by OLNOLAN
Hey Man, Did you drill the steam holes in the heads? Might have something to do with your issue. olnolan
Yeah I drilled the steam holes in the heads, thanks anyway.
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Old 01-06-2010, 11:46 AM
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Quote:
Originally Posted by sunsetdart
When using an electric water pump, you have to remember that they only push so many GPM(gals per minute). With a motor making HP, the pump can usually keep up when at idle but at speeds the pump is still only pushing the same GPM as it does at idle. Electric water pumps usually work ok for the street but can't flow as much as a belt driven. The temps will fluctuate especially at speed, at low speed they should even out.
I seem to have this temp spike everytime I use the car and it doesnt matter whether im sitting still or on the move. The car hasnt had alot of open road speeds as yet.
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Old 01-06-2010, 11:47 AM
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Quote:
Originally Posted by ap72
or you can just drill a 3/32 hole in your T-stat. warm up may take about 30 seconds longer but it solves the air lock problem. I drill a small hole in every T-stat I install just so there never is a problem.
Yeah I dd that before I fitted the T-stat, thanks.
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Old 01-06-2010, 11:49 AM
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Quote:
Originally Posted by Centerline
This is not necessarily true. A thermostat can intermittently fail which will cause the temp to go up within a few seconds and then come right back down. Years ago I had a new Dodge with a 318 that had less than 400 miles on it do just that. An intermittent spike in temp and then back to normal. Did it several times over a week or so until I changed the thermostat and that solved the problem.

Whenever I build an engine now days I always install a thermostat that if it fails it will fail in the full open position. Much less chance of overheating that way.
How do install a thermostat so its going to fail in the open position? You cant know if its going to fail open or closed?
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