Erratic Temperature Reading in Perkins 4.108

[jlogan]

Just to finish up the story...I acid washed the heat exchanger with one gal of muretic to 4 gals of water...took the hx off the boat (tough to do on the Gulfstar 37)..used eye, hand protection with running water nearby just in case...dipped it in the mixture for maybe 5 minutes total, which removed all the deposits and old zinc residue and whatever...rinsed in fresh water, then bucket of water and baking soda to totally neutralize any acid...painted with ford blue paint (close enough). Back on the engine, usual struggles with getting all hoses connected while working in a space you would have to be three feet tall to work in correctly...got new end cap and gasket from TAD, very friendly people, give them a call if you need anything. Run at dock now up to 2000 rpm, never goes over 180. It is a lot of trouble to remove the hx from the transverse mounted ones in the Gulfstar, but it is the best way to make sure the heat exchanger is not the problem.

There really didn't apprear to be any blockage, but there was a lot of bubbling initially, so there must have been a lot of carbonate buildup from the seawater that was making the difference...when I ran it at dock before at same rpm, would slowly overheat...

Did have the usual air block problem common to Perkins when putting fresh coolant into the engine, you have to fill it up, run it a minute or three, and then check the coolant level in the header tank again...it will usually hold another half gallon or so...if it is not right, you will get an overheat signal very quickly as the temperature sensor will be reading steam temperature, not water temperature..

anyway, worth the effort if you have the typical overpropped, overheating perkins in an older sailboat...do it before you start tearing into thermostats, temperature sending systems and replacing pumps...although replacing the pump on an older engine usually helps. Mine is fine, the water dumping out the back of the boat at the dock with the rpm at 2000 is barely warm now, so removing the flow restrictions through the hx definitely helps.

NOTE: THE ACID WASH TECHNIQUE IS DANGEROUS. DO NOT USE THIS IF YOU ARE NOT SURE OF WHAT YOU ARE DOING, AND USE EYE, BODY, AND HAND PROTECTION...ALSO, WHEN YOU DISPOSE OF THE ACID WATER MIXTURE, MAKE SURE TO NEUTRALIZE THE ENTIRE 5 GALLONS WITH BAKING SODA TO THE POINT THERE IS NO REACTION...THEN USE LOTS OF WATER TO DILUTE..DON'T JUST DUMP IT ON THE GROUND OR IN YOUR PLUMBING...

[SkiprJohn]

The biggest contibutor to people being unhappy with the size of their engines and the engine overheating is too large a prop. An 18 inch prop is way oversized for the 2:1 gearbox therefore the engine would never develop the hp because you couldn't get the revs up due to overheating. Changing an engine is quite a bit more expensive as compared to having your prop cut down or just buying a smaller one on eBay and giving it a try.
JohnL

[SkiprJohn]

Did anyone mention thermostat yet?
JohnL

[S/V Antares]

The Perkins 4-108 came with VDO Senders and a VDO Gauge panel. The VDO senders have the Max temp range, Mfg date and Partial part number stamped the hex flats (Where the wrench goes). If it says 120 Deg C (250F) your gauge should be a VDO with a max scale of 120 (250F). Most US gauges will read incorectly. If you change to a Teleflex etc. you should make sure the sender matches. Temp senders have no moving parts and seldom fail. That said It looks like you have a handle on it (HX). I had a Gulfstar 37 and sailed it several times to the Caribean. Nice boat.

[northiceman]

Have a 17 in Prop with a 13 in pitch (Pitch is a big factor in how the engine power is dissipated thru the drive line. Borg-Warner 100 (2:1 reduc). I run this engine at 2800 rpm and no overheating. Have been doing this since 1996. Engine temp is typically around 185 - I don't get too concerned if it sometimes hits 195 (which isn't very often). Typically happens if the waves are high, AND can be influenced by the water temp around the yacht. I think (not sure) that if the motion gets a bit violent that the water flow may be a bit more erratic than normal - maybe the wet exhaust provides a bit more back-pressure ?
The temp has gone to about 220 and that was when I stopped and found seaweed in the primary sea-water filter (Groco 1000).
The engine has the Bowman Classic cooler (along side of engine on top).
I was told by some expert at MArina Del Rey (about 5 yrs ago) that it is the best cooler for that model 4-108.