Over the Holidays I installed a new 383 SB crate engine from GM. I used Eldelbrocks Multipoint fuel injection system. Every thing seems to be runnning normal Except for the cooling system. No overheating problems! But when the engine reaches thermostat temp I get this weird pulsing in the cooling system. Somtimes its so hard you can hear it as well as fell it in the hoses. It is the most pronounced in the Line coming from the intake to the heater core. Somtetimes I can feel it from the drivers seat when I stop at a light. The system will purge a small amount into the purge tank when the thermostat opens the 1st time.
We (a mechanic friend of mine) have presureized each cylinder to check for air in the radiator, and I had a guy test the system for Hydrocarbons in the radiator and I have changed the oil twice, once at 50 mile and again at 500 mile. I even replaced the water pump and the thermostate 3 times. NO ONE I have talked to has any ideas other than a head gasket leak. but it does not run hot and has passed the other tests for that problem.
Is this somthing I should worry about? Any Ideas.
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Ron Long

I had that same thing happen to me when I rebuilt the motor in my 67 Vette! I ended up putting a 160 thermostate in it! We fiqured the motor was running a little hotter than the gauge was reading and when the thermostate opened it was like throwing water on a fire but in a closed system and making that noise, but it stopped after the change!
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Mike,Charter DRSA Member

I droped to a 185 deg thermostate and it seemed to help
but did not cure the problem.
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Ron Long

I also replced the stock temp gauge with one from
Auto Meter, just to be sure and the gauges were very close
in readings. I have also monitured the system at length with a snap on analizer.
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Ron Long

Just a thought........
Make certain you have ALL of the air purged out of the system. Pick the HIGHEST point in the system you can let air out of(like a heater hose) and try "burping" it,when the engine is warm and NOT running.
$.02
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You call me freak like it's a bad thing......

I have a fairly large capacity radiator (truck) and my SBC would do "noises" when first warming up and would also go from close to 200º to flat cold when the 180º thermostat opened. this along with sucking the top hose flat at high RPM when the engine was cold and then it would close completely and go through the heat up process again and some times a third time. This made me decide the thermostat was just doing too good a job of shutting off the coolant flow. so I took it out and drilled a .125" hole in it for a small bypass. That quit the gurgling and wild temp changes while it was warming up because it bled some hot water into the radiator before the stat opened so there wasn't such a gross temp change when it did open. Now it works in a mor "refined" way except on really cold (really cold here in So.Cal. is anything under 50º..) nights it will run at 160-170º telling me the stat isn't opening at all, just cooling on the 1/8" bypass hole. I run a temp guage in each head of the SBC.

I think someone already beat me to it, but drill a larger bypass hole in your thermostat.

Justice


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I like it loud, fast, $ shiny!

Thanks to everyone who has responded.
I have thought about the bypass hole in the thermostat, Stewart even makes one like that----But since the connection for my heater core comes off almost beside my thermostat in the intake, dosent that act like a bypass?
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Ron Long

Yes....it does. A small hole in the thermostat will "leak" or "bypass" coolant into the radiator under all conditions. This can be good and is a recommended addition when running high performance water pumps. But, it can be overdone to the extent of defeating the operating temperature range of the engine.

I am with the "it's air" crowd on this. The only way it can make noise is with air! So, add water wetter to the system which helps air entrapment, and burb the system. Make sure to have the heater coil "on" and in circuit to purge the air there too. If this does not get it, raise the front end of the car/truck to help air escape from the block.

You can drill 1/8" holes in the thermostat as the picture shows.

Do not however, close the system up when warm or hot....another story for another day.

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Steve Jack
Marketing Technologies Limited,LLC
ConceptOne Brackets and Pulleys

THANKS FOR THE HELP,
Problem solved, Added water wetter, raised the front of the truck and refilled the system. Runs great!

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Ron Long