Water Temp vs: Head Temp

[Al Schober]

I may be chasing a non-problem, but would like some second opinions.
I changed from SW to FW cooling using the Moyer kit over the winter. System is still running without a thermostat until I get comfortable with it. This year the system has been running hot - cruise speed under power has been limited to keep the gage under 200. I finally realized the system was losing coolant through the water pump, and perhaps running with low coolant level. A rebuilt pump was installed, which still dripped. Finally I bit the bullet and installed a new MMI coolant pump. Another thing I've been doing recently is to check temperatures with a non-contact infra-red thermometer (Radio Shack 22-325).
Today I installed the new coolant pump, cleaned the temp sender unit, filled the system, and then ran it dockside in gear at 1400 RPM. The temp gauge finally stabilized at 160F. Other temps measured with the IR gizmo were: SW in 73F, SW out ??, coolant in 98F (at pump), coolant out 125F (at exh. manifold elbow), aft/port end of head 152F, stbd of #1 plug 176F, fwd end of head 196F (to port of temp sender).
I'm not sure what to make of these numbers. First thought that coolant out at 125F is wonderful - ignore the others. I expect the metal to run hotter than the water, otherwise there's no heat transfer. Also, the port fwd end of the head has basically no circulation so will run even hotter. And the temp sender is driven as much by the temp of the head as the temp of the coolant.
So, question #1. What is the real temp limit on things? Obviously you don't want to boil the coolant, but I'm far from that! What about the temp to warp the head? What about the temp to affect the head gasket? What about the temp to burn the paint off the head? What haven't I thought of??
The gauge temp I know how to fix. Pull the sender out of the head, plug the hole, and install the sender into the outlet of the exhaust manifold with a tee. That will give me an accurate read of coolant temp.
I guess question #2 becomes: Has anyone else checked head temps vs water temps?

Al Schober

[David Masury]

I have a fresh water cooled system... came with the boat. I can understand your question though. The coolant temp should and will always be lower than the coolant temp in the head. The realtionship between what is going on will reflect just how efficient the fresh water system is.

On my boat, I have to run it for a very long time under load before the coolant temp goes to 140. Back at idle it will go down to 110 ish. I know that the temp at cylinder #1 is about 180 as I have a 180 thermostat and I have checked it there. The only real variation is when the water temp that I am motoring through changes like in late summer when the harbor really warms up, then I may see a small rise in the coolant temp. But that goes away once I motor through open waters.

From what you describe, it sounds perfectly normal. Go out and enjoy your boat.

David

[Marian Claire]

My system is a little none conventional. Even so when the water temp is 160 the head reads 180. I use an oven thermometer to check the head temp. Dan S/V Marian Claire

[Al Schober]

Just another data point. A google on 'cylinder head temperature' turned up a bit of info, all from folks flying airplanes with aircooled engines. They use thermocouple devices that install around the spark plug threads to keep an eye on things. The lowest temp limit they seem to adopt is 400F for an actual temperature of the metal of the head. Above this, there seem to be cases of scuffed pistons and actual seizure of the piston in the cylinder.
I think I'm going to move my temp sensor to the outlet from the exhaust manifold. I'm thinking that this will give me a better picture of what the engine is really doing. If a local spot here or there are getting hotter, so what as long as I don't boil my coolant. Then again, if you see a Tartan 30 surrounded by a cloud of steam on Fishers Island Sound, it's probably me.

Al Schober

[dvd]

Al,

I'm sure there are plenty of things going on any any engine that the average person just doesnt need to know. Typically the A-4 can be managed with the few normal information guages that usually come with all boats. I think we could all probably manage the engines quite well with just the coolant temp and oil pressure. As long as these 2 areas are monitored and stay within normal limits your A-4 will probably run fine for a long time

I say to just go out and enjoy the boat. Its really not rocket science.

DVD

[Silverheelsii]

I have a similar problem with my FWC system.My cylinder head runs about 220 to the right of the plugs and 250 to 350 to the left of cylinder 1. Under a hearty load it really heats up and starts to ping like in pre-ignition. Recently, I discovered if I put a water soaked rag over the spot within a minute the pinging stops. The overall water temp is 160. All temps measured with an IR thermometer. I think I have some blockage in the head. I discussed this with Tom at Indigo Electronics and he suggested replacing the head with a new Moyer head since mine is probably 40 + years and ran salt water must of its life. Any thoughts?

[joe_db]

I have two or three threads with all kinds of temperature measurements relating to my FWC conversion.
Long story short: I have no thermostat in the old housing and have the bypass blocked off. I have a T in the head and an alarm on one end and the electrical sensor on the other. I found the best place to measure COOLANT temperature was the top of the thermostat housing and at the heat exchanger itself. The side of the head next to the manifold - port side in a normal setup - has the valves and not much room for water passages. It can be much hotter than the coolant. That is to be expected with little water over there and the exhaust valves.
The temp sender does match my IR measurements, but it takes awhile. The coolant doesn't really flow in the T and it takes some time to match the engine temps. I may get around to moving it to a place with more active flow going by it.

[joe_db]

I agree with Tom. Sounds like blockages.
Hot tanking the thing might work, but it is likely nearly corroded through by now.

Originally Posted by Silverheelsii

I have a similar problem with my FWC system.My cylinder head runs about 220 to the right of the plugs and 250 to 350 to the left of cylinder 1. Under a hearty load it really heats up and starts to ping like in pre-ignition. Recently, I discovered if I put a water soaked rag over the spot within a minute the pinging stops. The overall water temp is 160. All temps measured with an IR thermometer. I think I have some blockage in the head. I discussed this with Tom at Indigo Electronics and he suggested replacing the head with a new Moyer head since mine is probably 40 + years and ran salt water must of its life. Any thoughts?

[joe_db]

Just did a test yesterday before eating the turkey:
The top of the thermostat housing stayed about 6-10 degrees cooler than the actual coolant in the heat exchanger. Say 100 degrees on the housing and 108 for the coolant. They track pretty close and some of this is do the way IR works. Different materials and colors all effect the rate of IR emission. Note the industrial IR meters are way off on skin.
Another note - any IR metering off the head is the METAL temperature at the surface. The only exact measure of the coolant is the coolant itself