View Full Version : Hornet Cooling issues?

07-07-2011, 11:14 PM
I have the original 350 Chris Craft 320 hp engine in my 1972 Hornet. I have been fighting intermittent cooling issues. It has a new impellor, the thermostats are working properly. ( I removed them and set them in water and they open at 140 degrees. ) My gauge will get up to 180 degrees and I get steam rolling off of the stern when idling with the boat. When I get up and run at above 3000 rpm, the boat cools back down to 160 degrees. Any thoughts on what else I can do?

07-07-2011, 11:33 PM
does the motor have a circ pump and a raw water pump or is it setup with a crossover?

is it a sherwood pump? how is the cover is it worn?does it have the paper gasket in place.

we just troubleshoot cooling issues in a 71 cc motor

07-08-2011, 07:00 AM
Do the risers still have the Chris Craft relief valves? The risers with the valves have fittings on them connected to each other by hoses, there are pop off valves in the hose housings. If one has lost the disc, broken its spring or being held open by debris it can cause what you are describing. If one or both are faulty they will dump needed cooling water, like you describe is only over come by getting the RPM up to supply the extra needed water.


If you have the riser pictured at the top you have the relief valves.

07-08-2011, 07:34 AM
Yes, this cooling system has the pressure relief springs. We took them off and cleaned them and the housings. I was told that these pressure relief springs are no longer available. One spring seems to have less tension then the other when we were testing them, so that may be the issue. If this is the case, then what can I do to continue to use this system? Any ideas on who may have these pressure relief springs? My water pump housing, gasket and housing surface and not showing any signs of wear. (we used a new paper gasket when replacing the impellor).
I really appreciate everyone's thoughts and help on this!

07-08-2011, 06:27 PM
The valves were to relieve pressure in the block, head gaskets back then were not as good as today. They kept the block pressure quite low and did insure plenty of water flow. When we did a valve job with better head gaskets we would eliminate the valves, one less head ache. Keep and eye out on Ebay they do turn up now and then. There may also be a dealer with some kicking around.


Here is a diagram of your setup, they do not show the valves but have the gaskets listed!

07-09-2011, 08:58 AM
The 1971 350 cc motor we have we got rid of the cc manifolds and went to stainless marine risers and crossover system. the performance gain was well worth it not to mention the weight savings the looks were the gravy. we kept the original manifolds incase the next owner was interested in originality.

that motor had a raw water pump and a circ pump with iron plumbing we scrapped all that and now only use the circ pump, so we got rid of alot of weight.

07-10-2011, 10:53 AM
A word to the wise, if the head gaskets are original removing the relief valves can add enough pressure to get the head gaskets leaking leading to a bigger job.