Water can't compress and the water pump flows at a constant rate. So if there is a surge it much be caused by air compressing in the system somewhere.... When I had a rear radiator in my truck I tried everything I could think of to get all the air out and ended up parking on a very steep hill and pulling the heater hoses off the heater core then putting a hose adapter I made in one of them and bleeding the air out of the other. Once I found that trick I never had any issues again. The only thing I changed from stock was to use a factory water pump pulley that was a bit smaller than what was on there.
