Wildwest
Member
You have a 160 deg. thermostat.
Lehman 120 only gets to 160 degrees
- Thread starter Dave_E
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You have a 160 deg. thermostat.
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Dave_E
Senior Member
No... Dealer sold me a 180 deg thermostat. Read my post, later read 178.
SteveK
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IF you have a 180 t-stat, you should read 180* above it with Infrared
SteveK
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problem solved
Transaxial
Senior Member
I was going to suggest adding a mechanical gauge as a second reading but Larry M beat me to it! I think he is referring to the capillary tube type which is a sealed unit and eliminates some of the inaccurate readings you can get with electric gauges for the many reasons already mentioned. I have added these in vehicles that I don’t quite trust the dash gauge on and the PO added one in the doorway to the engine room in my boat. At some temperatures the two gauges read pretty close and sometimes they are 15 degrees apart. It is peace of mind to have the second gauge to verify temperature.
I had a lot of trouble with low temps (140-160) on my 6.5 liter old school Mitsubishi. Very much like a NA Ford Lehman. There were 4 used but still working thermostats on the boat when I bought it. I added another and still had erratic temps. Too cold. Too hot to the point of boiling over. I think my thermostat housing was not right and not allowing full flow at higher rpm. But at lower rpm the thermostat must not have been closing properly. I finally designed my own system with a new Fernstrum keel cooler and an Amot style bypass valve all plumbed with 2” fittings. Now it is responsive and cools very well but is slow to warm up with full 2” flow when the thermostat is closed. Just saying there can can be more to it than changing a thermostat.
I had a lot of trouble with low temps (140-160) on my 6.5 liter old school Mitsubishi. Very much like a NA Ford Lehman. There were 4 used but still working thermostats on the boat when I bought it. I added another and still had erratic temps. Too cold. Too hot to the point of boiling over. I think my thermostat housing was not right and not allowing full flow at higher rpm. But at lower rpm the thermostat must not have been closing properly. I finally designed my own system with a new Fernstrum keel cooler and an Amot style bypass valve all plumbed with 2” fittings. Now it is responsive and cools very well but is slow to warm up with full 2” flow when the thermostat is closed. Just saying there can can be more to it than changing a thermostat.
GrandBanks42
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Yep. Even at idle speed, if your thermostat is working correctly, the engine should eventually get up to normal, operating temperature.
A lot of people have the mistaken notion that the cooler your engine runs, the better it is. Not at all true! I once knew a guy (who THOUGHT he knew a lot about engines) who said that you should just remove the thermostat, so the engine can run as cool as possible. Dumb, dumb, dumb!
Question only for knowledge sake for me, I’ve heard this many times “cooler is better” and knew that was incorrect but not sure why. Why is that? I’m an old jet engine mechanic with very little gas and even less Diesel engine experience.
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Dave_E
Senior Member
Update on the coolant temperature indicating system on the good ship. This is now a QUEST. Here's what I did, results and where we're headed. Purchased the dual sender recommended by Sierra. Installed and both gauges read 200+ when the engine had only run for 15 minutes and the IR GUN READ 145 DEG F. I tested each gauge (removed the Sensor wire and grounded the terminal, gauge went past 240 (which it was supposed to do), removed ground, gage went back to the bottom of the range (again, what it was supposed to do). Checked ships wiring, found lots of things that needed fixing (like wires twisted together and wrapped with electricaL tape - YIKES 
). Then things started getting weird. I purchased another new sender, and as soon as it hit 150 deg on the IR gun, it's like everything just quite. I got NO signal from the sender. I removed ships wiring and ran a wire from the sender straight to the gauge and got NOTHING. I'm ready to believe I got a sender that failed in an open position, 30 minutes after it was installed? I WILL solve this mystery.
Dave
). Then things started getting weird. I purchased another new sender, and as soon as it hit 150 deg on the IR gun, it's like everything just quite. I got NO signal from the sender. I removed ships wiring and ran a wire from the sender straight to the gauge and got NOTHING. I'm ready to believe I got a sender that failed in an open position, 30 minutes after it was installed? I WILL solve this mystery. Dave
sbman
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Update on the coolant temperature indicating system on the good ship. This is now a QUEST. Here's what I did, results and where we're headed. Purchased the dual sender recommended by Sierra. Installed and both gauges read 200+ when the engine had only run for 15 minutes and the IR GUN READ 145 DEG F. I tested each gauge (removed the Sensor wire and grounded the terminal, gauge went past 240 (which it was supposed to do), removed ground, gage went back to the bottom of the range (again, what it was supposed to do). Checked ships wiring, found lots of things that needed fixing (like wires twisted together and wrapped with electricaL tape - YIKES
Dave
Remember these senders create a variable resistance to ground. You can test the sender directly by disconneting it from any wiring and then using your meter on an ohms positions (1K or 2K range) and then checking from it's terminal to the engine block (for one wire sender). If it's a two wire sender, measure resistance between the terminals. That value will vary based on the temperature of the coolant in the engine. If it's a typical sierra sensor, they are rated at 339 ohms at 100F and 35 ohms at 220F. You can get the other values by charting a line between those two points, it should be a pretty linear relationship, I've attached a chart that illustrates that.
Start with testing the sender directly using your multi meter.
Next you can test the gauge with some resistors if you have them or can get them at a local electronics shop, hook the sense lead of the gauge to a 35 ohm resistor and put the other end to the gauge's ground, you should get a reading of 220F on the needle.
If you can't get a resistor, use the sender itself in boiled water, with direct leads for both ground and the signal directly to the gauge. Be sure not to completely submerge the sender, the signal terminal must be kept dry. You can use vice-grips to clamp the ground wire to the body of the sender.
If all that passes, then you have a wiring issue between the gauge and the sender.
I've calibrated analog-N2K adapters this way. I put the sender on a vice grip with the ground wire clamped onto the body, then put that on top of a coffee cup full of boiled water. The signal wire gets hooked up normally. I put a digital kitchen thermometer in the water and note the resistances of the sender every 20 degrees until the water reaches ambient temperature.
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Dave_E
Senior Member
Done
Well the skinny of the whole thing is Sierra brand senders and equipment are not calibrated instruments. Recreational marine instrumentation just isn't dialed in and calibrated like aviation stuff is (that's what I'm used to). Both upper and lower helm gauges work fine (even got 2 new ones to verify), I've tried 2 brand new Sierra sending units (dual station, same results with both) they read high, 200-210F when the engine is at 160F (using an IR gun). I'm running a 180F thermostat (new and a new tank cap). I also replaced the sending unit wire up to the helm. Then I put the original sender back in and both gauges read 160F when engine is up to temp out on a run (back to where I started). I left the original sender in. Hell of an exercise to come up with this conclusion...
Well the skinny of the whole thing is Sierra brand senders and equipment are not calibrated instruments. Recreational marine instrumentation just isn't dialed in and calibrated like aviation stuff is (that's what I'm used to). Both upper and lower helm gauges work fine (even got 2 new ones to verify), I've tried 2 brand new Sierra sending units (dual station, same results with both) they read high, 200-210F when the engine is at 160F (using an IR gun). I'm running a 180F thermostat (new and a new tank cap). I also replaced the sending unit wire up to the helm. Then I put the original sender back in and both gauges read 160F when engine is up to temp out on a run (back to where I started). I left the original sender in. Hell of an exercise to come up with this conclusion...
