"Hi Frederick & Noel. My s
"Hi Frederick & Noel. My set up at present is raw water cooling.
Last summer I ran this for about 10 hours with no thermostat, temps would never get above 140f (mostly never even got a reading on the gauge – new gauge and sender so they were working OK), too cold for my liking so flow now is:
• Water pickup through Volvo leg
• Fynspray ¾” pump driven at 50% engine speed
• Into Front of engine (where auto pump would fit)
• Out of engine via thermostat housing that has a pressure bypass that allows flow of coolant to bypass the block and head when engine is full of water and thermostat is closed. Thermostat is a 160f unit with 2 X 1/8” bleed holes drilled. The bleed holes allow air to exit and water to fill the engine before the pressure builds up and opens the bypass valve which allows water to continue to flow to the exhaust manifold and pipe when thermostat is closed.
• Into exhaust manifold at rear
• Out of exhaust manifold at front
• Into 2.5” stainless exhaust pipe at elbow at end of the exhaust manifold
• Exiting through stock Volvo 270 leg.
Ran this way for 7 hours in the last week. Temps oscillated between 140f and 190f at the rate of about 80 seconds (which was the thermostat opening and closing), sustained high speeds (5000rpm – 47mph just sitting off the rev limiter set at 5100rpm) for 15mins did not cause any variation in temps other than the 80 second oscillation becoming about 60 seconds, neither did towing 2 tubes or 3 slalom skiers. Boat is a deep V runabout weighing 980kg dry with 100 litres of useable fuel in tank up front plus 3 X 100+kg people and gear it would have been pushing close to 1500kg plus the drag of the skiers/tubes (about 2500-3000rpm towing speeds) – whilst I have not dyno’d this engine I have built plenty of other 265 Hemi’s that have been dyno’d and this combo would be pushing out about between 240 and 270 HP at 4800rpm and above 300ftlb torque from 2000rpm to over 4000rpm (probably a bit lower in the boat up top given the restriction of the 270 exhaust system, soon to be through transom exhaust) – starts hot or cold straight away (no choke needed) idles in and out of gear at 550rpm (baby cam, 4bbl carb, programmable wasted spark ignition, 9.9:1 comp). Not sure how much more I can stress the cooling system - certainly no problems with overheating using a thermostat with raw water cooling. Best part was I used about 90 litres in the 7 hours of running (started the week full and pumped out 10 litres using the electric fuel pump at the end of my holidays into a container)
Next time I have it out (probably Easter) I may change the flow to:
• Water pickup through Volvo leg
• Fynspray ¾” pump driven at 50% engine speed
• Into exhaust manifold at rear
• Out of exhaust manifold at front
• Into front of engine (where auto pump fits)
• Out of engine via thermostat housing that has a pressure bypass that allows flow of coolant to bypass the block and head when engine is full of water and thermostat is closed. Thermostat is a 160f unit with 2 X 1/8” bleed holes drilled. The bleed holes allow air to exit and water to fill the engine before the pressure builds up and opens the bypass valve which allows water to continue to flow to the exhaust manifold and pipe when thermostat is closed.
• Into 2.5” stainless exhaust pipe at elbow at end of the exhaust manifold
• Exiting through stock Volvo 270 leg.
The objective being to avoid the large oscillation in temps by preheating the water a little with the exhaust manifold first before water enters the block. However my exhaust manifold has a small leak into the exhaust system and until I fit a new manifold I don’t want to risk losing flow to the engine.
Further on I plan to fit a 4” X 16” heat exchanger I have here. This would be cooling the entire engine and exhaust manifold so that use in salt water becomes possible (Exhaust manifolds are alloy so hot raw sea water will rot it out pretty quickly if I don’t change it to closed loop cooling with the engine). Will be good to see how the temps go then.
My suggestions if you have over heating with a thermostat are:
• Check ignition timing is advancing properly and that you are getting a total advance of around 30deg all in around 3000rpm (assuming compression ratio of around 9.5:1 on regular unleaded fuel) Too little timing will cause higher temps in these engines – too much will destroy pistons though. For sustained high loads (say above 60% throttle) I’d suggest running N9Y plugs as well.
• Check fuel mixtures (carb jets) – around 12.5:1 AFR under load, too lean will increase temps.
• Check compression in each cylinder to make sure all are OK
• Check thermostat is opening and closing properly.
• Check heat exchanger has the correct capacity for the engines output (and including sufficient cooling capacity for the exhaust manifold if it’s in the closed loop)
• Check flow of water – is the heat exchanger before the exhaust manifold if the manifold is raw water cooled – if so try plumbing it after the engine.
• Check the bottom hose from the exchanger to engine pump, I have seen many of these look fine at idle and low speed that then suck in at higher revs if the spring inside has collapsed.
• Check the heat exchanger or any other part of the cooling system is not partially blocked in either loop.
• Check raw water pump is pumping properly.
Hope this above is of some help.
Cheers
Jamie"
