Front of cylinder head is correct place, not the bock, the little cheapo laser guns are real accurate, used to cost about £75, now peanuts.
Just a few thoughts for what they are worth. From memory your thermostat modulates in the range of 83-95 C. If motors operating at a TRUE 85 C them thermostat barely open. However you are correct to be concerned if temp gauge moves like the tacho when you give motor the beans.
Heat exhanger on Perkins Sabre is a bit marginal, has it been completely cleaned? I use ultrasonic cleaner to go the job.
We all crab Sherwood raw water pumps, however they do have 1/8th NPT test ports on them where you test for inlet restriction and pump output pressure. Not sure what test points your Jabsco has if any, however you want to see around 15 but no more than 20 psi on pressure side of the pump and about 5 psi at the 1/8th tapping on the gear cooler for your stern gland, pretty much the end of the cooling water food chain. Any more than 20 psi at the pump indicated that your cooling side is clagged up.
Just 500 or so hours seems very little time for wear in raw water pump, however you can always side for side the pumps to eliminate this one.
Re: water pump wear,I,ve done about 1300hrs and pump works fine altho I have changed wear plates and cam.This is using the boat in very silted waters.Rivers Trent ,Humber and Ouse.Have you changed the sensors from one engine to the other to compare?
Another thought,can you put a bucket under the exhaust outlets and time how long it fills,then try the other engine,or if not could you do where it comes out the engine? If you do dont gas yourself!!
Exchanger completely removed, core taken out and washed and each channel rodded out with soft wire, ditto with the oil cooler. To be honest both were clear apart from bits of loose powder - no solid chalking up at all. VP had already serviced the heat exchanger the year before. Putting pressure gauges on the pump is a bit outside my very amateur capability but I will have a look at the rwp to see if it has ports. I dont think the stern gland has a cooler - its a traditional stuffing box. the raw water circuit goes - inlet, pump, air charge cooler, gearbox oil cooler, exchanger, exhaust elbow and out. the turbo is dry
You describe the core problem exactly when you say the temp moves like the tacho when I open the throttle. However there is a lag of about half to a minute when I open up before the temp goes from about 83 to 90 but it drops back almost immediately when I throttle back
Switching the pumps is last resort as they are not simple bolt ons as I see it. gear driven and I think you have to replace some seals if you take them off as they are an interference fit (apols if this is gibbersih - as i say I am an amateur)
the water flow rate needs to be checked while under top/ high load, as the exhaust pressure is highest then, causing the greatest back pressure on the water pump. Idle / high idle would not be conclusive..
I have had differential wear on a twin installation, probably caused by the elbow on the pump, when the lesser worn one had straight connectors.
If not mentioned before is there a sufficient blead hole / jiggler in the thermostat, to ensure an adequate flow around the wax chamber in the early opening up phase?
How long have you run at the hot upper end? long enough for it to stablise?
are you running at equal boost levels, as boost pressure is a good measure of power being pulled from the engine?
Last edited by david_bagshaw; 05-01-12 at 17:57.
Not necessarily depends on the pipework arrangement a high exhaust pressure could help the pump due to venturi action.