Texasmark
Supreme Mariner
- Joined
- Dec 20, 2005
- Messages
- 14,795
As I was tweaking the used boat I purchased last summer, I had a nice set of Farina gauges on the dash but in the center was a 3" unused circle. Thought about what to put there......Since I was not familiar with the engine and the existing water pump was doing a fine job from idle on up, I thought about a monitor rather than fixing something that may not be/didn't show cause to be broken.....replacing the water pump impeller.
Most reading I do on boating forums list "water pressure" indicators fed by the little ⅛" NPT pipe female on the water jacket cover is what's talked about folks installing and using.
We all know that a displacement turned centrifugal pump (as a function of rpm) will have more pressure at high speeds and ram water entries than at low speeds. We also know that most cooling systems on 3-4 cylinder engines (to name a range where I boat) use temperature and pressure to control block temp. We also know that the thermostat controls block temperature till the poppet valve is forced off it's seat with increased pressure where the stat is bypassed and raw water is allowed to flow through the engine.
So I asked myself just what an I interested in knowing. Mercury design engineers, to name a company and my engine, decided that they were interested in engine temperature so they installed an "over temp" SPST switch set some 50*F above the tstat opening temp. So, I figured that I'd get a thermocouple that fit into the above mentioned port and install a temperature gauge. The thermocouple sends the signal on an electrical wire, not on a tube which can freeze or can squirt water in your lap like the speedometer tube did to me when the PO didn't have it connected and I didn't catch that fact till it was too late........, or get clogged with some foreign substance.
I did it and I can now watch my engine warming up, watch the stat open when the engine temp reaches that temp, get out in open water and get on plane and watch the temp drop down to ambient water plus some internal heat....100F with water at 55 at higher speeds after the poppet opens (for a number on my initial shake down cruise), then slowing down to off plane rpms and watching the temp climb back up to the tstat opening temp.
So, the point here, is I don't understand why everybody uses water pressure and not what the engine needs....it doesn't need water pressure per se, it needs to have the heat dissipated removed from the block to keep it at a desired temperature! I really doubt, till you experienced what I did, after all the years I have been boating, what a comfortable feeling it is to know what the temp gauge tells me.
This feeling especially comes from 2 events:
1. Purchased used boat. Maiden voyage just get past the no wake buoys and get an OT alarm.....what to do what to do. Decided to punch it and see what happens. Engine and boat respond and not long after the alarm extinguishes......ok fine. Make several trips around the lake and feel that the rest of things are working properly.....slow back down for no wake buoy and on comes the alarm......result of stuck thermostat shut.
2. Purchased different used boat. PO said the engine was "hot". He meant that the 70 hp Evinrude on the 15' Kingfisher bass boat pushed the boat really nice. What he should have meant was the the thermostat was corded and would stick shut at times. So this was back in the 1970-80 time frame as I recall, well before I knew all that much about mechanicing since my previous engines just didn't have problems and well before I was an iboats participant and had started repairing my engines that would develop problems.
So one day, I'm blasting along at WOT enjoying the ride as I had installed a new SS prop and had jacked the engine up one hole and all of a sudden the engine locked up......overrun clutch on the engine must have been inop also because had the boat had a windshield, I would have been wearing it for braces on my teeth!
---------------------
Yeah I could have avoided both problems but I was young and stupid back then and didn't know any better.
Most reading I do on boating forums list "water pressure" indicators fed by the little ⅛" NPT pipe female on the water jacket cover is what's talked about folks installing and using.
We all know that a displacement turned centrifugal pump (as a function of rpm) will have more pressure at high speeds and ram water entries than at low speeds. We also know that most cooling systems on 3-4 cylinder engines (to name a range where I boat) use temperature and pressure to control block temp. We also know that the thermostat controls block temperature till the poppet valve is forced off it's seat with increased pressure where the stat is bypassed and raw water is allowed to flow through the engine.
So I asked myself just what an I interested in knowing. Mercury design engineers, to name a company and my engine, decided that they were interested in engine temperature so they installed an "over temp" SPST switch set some 50*F above the tstat opening temp. So, I figured that I'd get a thermocouple that fit into the above mentioned port and install a temperature gauge. The thermocouple sends the signal on an electrical wire, not on a tube which can freeze or can squirt water in your lap like the speedometer tube did to me when the PO didn't have it connected and I didn't catch that fact till it was too late........, or get clogged with some foreign substance.
I did it and I can now watch my engine warming up, watch the stat open when the engine temp reaches that temp, get out in open water and get on plane and watch the temp drop down to ambient water plus some internal heat....100F with water at 55 at higher speeds after the poppet opens (for a number on my initial shake down cruise), then slowing down to off plane rpms and watching the temp climb back up to the tstat opening temp.
So, the point here, is I don't understand why everybody uses water pressure and not what the engine needs....it doesn't need water pressure per se, it needs to have the heat dissipated removed from the block to keep it at a desired temperature! I really doubt, till you experienced what I did, after all the years I have been boating, what a comfortable feeling it is to know what the temp gauge tells me.
This feeling especially comes from 2 events:
1. Purchased used boat. Maiden voyage just get past the no wake buoys and get an OT alarm.....what to do what to do. Decided to punch it and see what happens. Engine and boat respond and not long after the alarm extinguishes......ok fine. Make several trips around the lake and feel that the rest of things are working properly.....slow back down for no wake buoy and on comes the alarm......result of stuck thermostat shut.
2. Purchased different used boat. PO said the engine was "hot". He meant that the 70 hp Evinrude on the 15' Kingfisher bass boat pushed the boat really nice. What he should have meant was the the thermostat was corded and would stick shut at times. So this was back in the 1970-80 time frame as I recall, well before I knew all that much about mechanicing since my previous engines just didn't have problems and well before I was an iboats participant and had started repairing my engines that would develop problems.
So one day, I'm blasting along at WOT enjoying the ride as I had installed a new SS prop and had jacked the engine up one hole and all of a sudden the engine locked up......overrun clutch on the engine must have been inop also because had the boat had a windshield, I would have been wearing it for braces on my teeth!
---------------------
Yeah I could have avoided both problems but I was young and stupid back then and didn't know any better.