IR Thermometer and Temp Gauge accuracy

[mary]

Hello, I have gone through old threads to try to find an answer to my question, but haven't found the answer I need.

We have an engine with the FWC conversion. I just replaced both water pumps. They were both leaking. They appear to be doing their jobs now. Coolant is refilled and I've tried the thermostat bypass open and closed. The temp gauge is reading 180 before we even start the engine. When we start the engine, it appears to work correctly. Under load in the slip, the temp creeps up to about 210-220 on the gauge which would peg at 230.

We have an infrared thermometer, so I have aimed it at various points. Where would be an accurate location to read water temp to compare against the water temp gauge? Is there an accurate way to read CHTs? I'm getting readings around 240 some places around the spark plugs.

Do you have a FWC engine running well that you've tested with an IR thermometer and can share the readings?

Thanks!

[joe_db]

I have a ton of IR readings in some of my threads if you look.
Some quick answers:
1. Your gauge and/or sender are hosed up somehow.
2. The IR meter is tricky and depends on the material it is aimed at. I found testing the hot part of the heat exchanger and the actual coolant with the top off pretty good. I found the top of the thermostat housing a pretty good place to measure as well and obviously part of the engine instead of separate from it.
3. CHT is kind of a vague concept on a water cooled engine. Air cooled airplanes and cars have CHT gauges, but not water cooled ones. It is hotter around the spark plugs and over by where the valves are because there is less coolant flowing there. I have seen 240 or more right next to the plugs.
4. My temp gauge is accurate eventually, but slow. I have a T with the alarm sensor and it takes a few minutes for the temp gauge to track the actual temp.
5. IMHO your engine - if the gauge is accurate - is too hot. 220 degrees is very close to boiling depending on the coolant mix and pressure. We really have no idea how prone the engine is to steam pockets either, it was designed decades before IR test instruments were available and also was designed as a RWC engine running fairly cold.

[mary]

Thank you for the reply. I'm an air cooled airplane person first, still learning about this water cooled business.

I just ran it again to check the temps and coolant began to escape from under the cap.. yep it is too hot. Ugh. The side of the thermostat housing reads around 220, the gauge pegged (230) within a few minutes of running the engine in forward gear at 1300 rpm.

[JOHN COOKSON]

You have couple of problems: Overheating and broken gauge.

Overheating: Do you have a thermostat? If so it may not be opening.Sure sounds like it to me

To test the gauge: Disconnect the wire from the sending unit at the gauge. Power up the gauge*. The gauge should peg low. Using a short length of wire touch one end to the sending unit terminal of the gauge and the other end to ground. The gauge should peg high (0 resistance). It is also possible there is a bit of corrosion in the gauge that is preventing the gauge to peg low when it is powered up. If the gauge checks out OK let us know. Something may be shorted or partially shorted in the sending unit.

TRUE GRIT

*Remember the coil will be powered up too when the key or switch is in the on position

[joe_db]

Your engine is overheating quite badly at this point. That is about the temperatures you would see with no coolant circulation AT ALL
We need to start from first principles. Is coolant actually circulating?
I would also remove the thermostat and block the bypass off for now with a valve. The stock thermostat is a poor implementation when it works well and is prone to issues.
This kit is what you need from Moyer.

Valve CLOSED = max cooling. Once we get a baseline of engine behavior with the thermostat gone and the valve closed, we will know what the next step needs to be.
You really need to get on this - the A4 can take a lot, but eventually you will have a warped head, failed head gasket, or both

Thank you for the reply. I'm an air cooled airplane person first, still learning about this water cooled business.

I just ran it again to check the temps and coolant began to escape from under the cap.. yep it is too hot. Ugh. The side of the thermostat housing reads around 220, the gauge pegged (230) within a few minutes of running the engine in forward gear at 1300 rpm.

[tac]

Stewart-Warner Gauges

If your temp gauge is the original S-W gauge, 100-230°F, then the fact that it reads 180°F with the engine off is probably normal. Some models of the marine version of the Deluxe series of temp and pressure gauges had an internal mechanism that, on loss of power to the gauge (i.e. shutting off the ignition) would hold the gauge needle near its last position. S-W called this Bi-Torque. These gauges can be recognized by having 4 terminal posts, are slightly heavier, and have a longer, brass case.

With oil pressure, the pressure drops so quickly at shutdown that the gauge usual reads near zero. However, temperature changes so slowly that on shutdown this gauge may read its last temperature.

To verify this:
1. With a cold engine (ambient temp), the engine off, and no voltage to the gauge, note the temp reading.
2. Turn on the ignition/gauge power without starting the engine. The temp reading should immediately drop to 100°F or just below.
3. Start the engine. As time passes the gauge needle should slowly climb.
4. Shut off the engine/gauge power. The gauge should read near its last reading.
5. Wait a few seconds, then turn on the ignition/gauge power, without starting the engine. Because there is no water circulation in the engine, the temp reading may climb as the water picks up heat from the block/head.
6. Further testing for gauge accuracy can be done by removing the sender, hooking the gauge up to sender and battery, and putting the sender in a pot of water at various temperatures, checked by a known, good thermometer. Don't use the IR meter to measure water temp. The emissivity of water is .67, far below the .95 of most inexpensive IR meters. S-W claims their temp gauges are 5% accurate. They don't say if that's 5% of reading or 5% of full scale. 5% of a 180°F reading is +\- 9°F. 5% of 230°F full scale is +\- 11.5°F.

Using an IR meter to compare with the gauge sender temp is problematic. The sender sits in the head surrounded by a large mass of metal. The actual sensing portion of the sender projects a bit and is surrounded on 3 sides by slow-flowing water. The sender tip is measuring mostly water temp. The IR meter is measuring the temp of a large mass of metal separated from the sensor tip by at least 1/2 inch of iron. I expect the metal will be cooler than the water.

[mary]

Thank you for the replies, everyone.

I do have a thermostat. I pulled it last night and soaked it in vinegar. Should I put it back in or leave it out? I'm thinking I will leave it out, close the valve and run it the same as I did yesterday for a comparison, though I'm open to suggestions..

I have the bypass valve kit installed and ran the engine with the valve closed and open. When I ran it last, the valve was open. Temps also got hot (less hot) when I ran it with the valve closed, but I don't remember the power setting.

John, I checked the gauge like you describe awhile back with someone in the cockpit looking at the gauge. It tested OK. I should have mentioned that in the first post.

tac, I'll check those points when I start it next. It reads 180 when engine off and no power to the gauge. When I turn the key (power to gauge), it drops down around 100 and when engine is running it slowly climbs to a temperature too hot for comfort. I'll have to watch for the rest of the items you listed. Thank you for the IR info.

As for the water flow.. if I have the cap off of the heat exchanger and I can see coolant moving through with the engine running, would that indicate flow?

There is water coming out the exhaust as it should.

Should I pull the fittings from the manifold and check them for blockage? Would krap buildup be an issue with a freshwater converted engine, or am I looking for a piece of an impeller?

[joe_db]

When I ran it last, the valve was open

That makes the engine as hot as possible.
I would try valve CLOSED and thermostat OUT and see how you do.

As for the water flow.. if I have the cap off of the heat exchanger and I can see coolant moving through with the engine running, would that indicate flow?
Yes, that indicates coolant flow.

There is water coming out the exhaust as it should.
That indicates raw water flow.

Thank you for the replies, everyone.

I do have a thermostat. I pulled it last night and soaked it in vinegar. Should I put it back in or leave it out? I'm thinking I will leave it out, close the valve and run it the same as I did yesterday for a comparison, though I'm open to suggestions..

I have the bypass valve kit installed and ran the engine with the valve closed and open. When I ran it last, the valve was open. Temps also got hot (less hot) when I ran it with the valve closed, but I don't remember the power setting.

John, I checked the gauge like you describe awhile back with someone in the cockpit looking at the gauge. It tested OK. I should have mentioned that in the first post.

tac, I'll check those points when I start it next. It reads 180 when engine off and no power to the gauge. When I turn the key (power to gauge), it drops down around 100 and when engine is running it slowly climbs to a temperature too hot for comfort. I'll have to watch for the rest of the items you listed. Thank you for the IR info.

As for the water flow.. if I have the cap off of the heat exchanger and I can see coolant moving through with the engine running, would that indicate flow?

There is water coming out the exhaust as it should.

Should I pull the fittings from the manifold and check them for blockage? Would krap buildup be an issue with a freshwater converted engine, or am I looking for a piece of an impeller?

[tac]

Infrared Thermometers

For more stuff on IR guns, see:

http://www.moyermarine.com/forums/showthread.php?p=97787#post97787

[mary]

I closed the valve and left the thermostat out.. I was able to compare it against yesterday running it with the valve open and thermostat in. I was curious if the check valve supplied enough back pressure to cool it or if I had to completely close the ball valve.

I gradually ran it up with more RPMs in forward gear and watched the temp closely. 1500-1600 RPM in forward gear got the temperature to rise above 180 after several minutes. The RPM maxes out at about 1700 RPM in forward. When it got to 190+, I reduced RPM and the temperature cooled.

It seems like the temp gauge is working.

Is it OK to always run with the valve closed?

[joe_db]

190 is OK for FWC. It is fine to always leave the valve closed, that forces all coolant through the engine.
We have a couple more issues to sort through. One is 1700 RPM is very low for max RPM. I can hit around 2400 or so at full throttle. What is your manifold pressure at 1700? What RPM do you get at 5 inches (25 inches aircraft type gauge)?
I am also a bit concerned at hitting that temp at low power in winter. If I run for one hour at 2100 RPM/5" with a fully closed valve I will see about 110-120 degree temps in chilly water. I literally cannot get my engine anywhere near 180 right now if I tried even at 0" with the valve at full cold. You also mentioned coolant spitting out of the cap? If my cap is on, it takes 7 PSI to open it and then the coolant will go through a small hose to the overflow tank.
We're getting there - keep at it

I closed the valve and left the thermostat out.. I was able to compare it against yesterday running it with the valve open and thermostat in. I was curious if the check valve supplied enough back pressure to cool it or if I had to completely close the ball valve.

I gradually ran it up with more RPMs in forward gear and watched the temp closely. 1500-1600 RPM in forward gear got the temperature to rise above 180 after several minutes. The RPM maxes out at about 1700 RPM in forward. When it got to 190+, I reduced RPM and the temperature cooled.

It seems like the temp gauge is working.

Is it OK to always run with the valve closed?

[mary]

Thank you joe

I don't have a manifold pressure gauge.

My best guesses are that the prop is limiting the RPM and/or it has a garden of seaweed growing on it. It gets more RPMs in reverse. The water temp here is about 50F. Not sure the relevance of any of that!

I found that the coolant cap wasn't on all the way when the coolant spurted out. It didn't seem to go into the overflow much.

I just added some MMO (a couple glugs to a 1/4 full tank) to the gas with the engine running and after a few minutes, blueish smoke (don't think it is steam) began to escape out of the exhaust and I saw oil on the water. Should I pull the spark plugs to check them, do a compression check and add some MMO to the cylinders while I'm at it? I don't see any oil in the coolant or water in the oil. I did notice a very tiny seepage of coolant where (I think) the head gasket is below the thermostat housing and to the left of the water temp sender. I've attached a pic. It only appeared when the engine briefly got quite hot yesterday and is no longer seeping. Is this cause for worry about the head gasket?

I'm beyond my scope of engine knowledge here, but I do want to understand it and learn. I really appreciate the help!

tac: your SW gauge description is spot-on and clears up some confusion. thank you

[joe_db]

I cannot tell from that photo if the seepage is old or new. I would do a compression check and check the oil for water contamination. If those two are fine, I would not worry about it for now.
You do need to check your running gear to see why the RPM is so low.
Also note heat exchangers can get clogged on either the raw of fresh side. I had to clean mine out.

[mary]

Here's a video of the smoking exhaust and raw water exiting. There's also a bit more seepage of coolant in that same spot that I uploaded a photo of again.

https://www.dropbox.com/s/9kehl18ivxshgoe/IMG_2566.MOV?dl=0

[mary]

I removed the spark plugs. The inside of the cylinders and spark plugs look dry. I put some MMO in the cylinders.