75 HP water pressure guage?

[coktoastin]

The boat and 1977 chrysler magnapower 75HP motor are new to me. No guages installed so I figured temperature would be a good place to start. There appears to be a probe in the water jacket with an orange wire coming form it. Is that for a temp guage? Also, I removed the 1/8 npt plug at the top of the water jacket/head and installed a male tube npt adapter. I ran tubing to a water pressure guage. Fired up the motor...no pressure. I pulled the line off the guage and fired her up again. I felt just a slight amount of air (somewhat exaust smelling) coming from the tube. Is that normal??? Is there supposed to be water coming from the engine into the tube and then to the guage. Again, I'm a newbie so any advice would be much appreciated. Thanks -Steve

 

[novicetech]

Re: 75 HP water pressure guage?

Hello and welcome to i boats, you say you installed a water pressure guage on this motor? <br />I am not trying to insult you but you did have the boat in the water or at least had the motor running on a set of muffs? Do you have a service manual for this motor? If you did not have a water source hooked to the motor your waterpump impeller was probably picking up exhaust from the motor leg. If you did have it running without a water source you will have to change the impeller.

 

[Realgun]

Re: 75 HP water pressure guage?

That the overheat sender. Try grounding it and see if the horn under the dash goes off. There is also a test to see if it closes when at the proper temperature also.<br /> <br />Best bet is test the overheat sender and make sure it works. You may glance at the guage to late to really know the motors too hot!<br /> <br />Would be better to get a tach to know what RPM you running at WOT.<br /><br />You may need a 20 pole and they are hard to get.

 

[coktoastin]

Re: 75 HP water pressure guage?

Novice tech and realgun...thanks for the replys. As I am new to the world of boats and outboards, any and all advice is much appreciated and I will not be at all offended or insulted. That being said, I did have muffs and a hose hooked up to the engine and there was no water pressure indication. After removing the hose from the guage and running the motor with a water source, there was nothing coming from the hose. I didn't run it long for fear of overheating. As far as the manual is concerned...one is on the way! <br /><br />Regarding the overheat sensor...there is an orange wire coming from it through the wiring harness to the dash but it isn't connected to anything. Will a normal temp guage work or is that just ment to set off a buzzer at a predetermined temp? <br /><br />Finally, regarding the tach. I keep reading about a 20 pole tach or tach adapter. How to I determine if I need one?<br /><br />Again, much thanks! -Steve

 

[novicetech]

Re: 75 HP water pressure guage?

There is a hole in the middle of the motor leg about six inches below the cowl, did you have any water coming out of this hole.

 

[coktoastin]

Re: 75 HP water pressure guage?

novicetech... No, I did not have any water coming out of that hole...??

 

[roscoe]

Re: 75 HP water pressure guage?

Sounds like it is time for a waterpump.

 

[Realgun]

Re: 75 HP water pressure guage?

I just replaced my pump and it was is good shape just two or more years old. I never got any water outa the holes in the rear till I put it in the water.<br /><br />The alternator you have is a 20 pole alt. You will need a 20 pole tach. <br />You will need to search for 20 pole in the catalog HERE there are 2.<br /><br />AS I stated above you will need the key on then ground the overtemp sender. This will cause the alarm to go off. That how you check the circuit. To test the sender you need to heat it up and monitor the temp to see if it does what it is supposed to do.

 

[coktoastin]

Re: 75 HP water pressure guage?

Thanks for the info and replys. As the engine is new to me and I have no maintenance history, I figured it might be a good idea to replace the water pump. <br />I ordered a maintenance manual but it hasn't arrived yet. Any suggestions on how to start the process of replacing the pump? Thanks -Steve

 

[chuckz]

Re: 75 HP water pressure guage?

The orange wire from the sensor goes to the orange wire on the terminal strip on the side of the engine. That connect the overheat sensor to the alarm. The alarm sounds when the sensor grounds the orange wire. You can test the alarm by grounding the orange wire at the terminal strip with or without the sensor connected.<br /><br />It sounds like the previous owner had an overheat problem and disconnected the sensor instead of fixing the water pump.<br /><br />The SS plug you removed is the port for the pressure gauge. If the water pump is working, water should have been squirting out of that port.<br /><br />Buy a water pump rebuild kit, not just the impellor. It sounds like the pump has been running dry. Hopefully, no engine damage was done by overheating.

 

[coktoastin]

Re: 75 HP water pressure guage?

L.I. Chuck, <br />Thanks for summing all that up! I traced the orange wire and it does go from the sensor, to the terminal strip, then through the wiring harnes to the instrument panel where it was conected to nothing...the end of the wire was taped off. It appears the engine wasn't originally mated with this boat and there are no guages or alarms installed on my instrument panel...they've been removed. Is there a special alarm or will any 12volt buzzer work? Also, can I put an actual temperature sensor i.e. one that will send a full range temperature signal to a temperature guage? It sounds like the one installed won't show a range of temperature, and that it just functions when it reaches a certain (too hot) temp...is that correct? <br /><br />Also, any idea where I can order a water pump rebuild kit at a good price? <br /><br />Thanks, -Steve

 

[novicetech]

Re: 75 HP water pressure guage?

Steve, the water pump impeller is not that hard to replace, if I am correct i think there is just five bolts holding the motor leg on. there is four that you can see, and then one longer one that runs through the exhaust snout. My motor is a 1970 and chryslers did not change that much in the seventys once you get away from the ignitions. Any way tilt motor forward as far as possible then remove those bolts and lower unit should come down. hold on to the lower unit, when removing the last bolt. Then when you get it off. in the middle of the drive shaft there will be a square looking thing, with four bolts holding it down remove the bolts, and pull up on the water pump housing. Under this housing is the impeller. There is a key that holds this impeller onto the driveshaft be careful not to lose it. To install new impeller make sure you lubricate the fins with dishsoap and when replacing the housing on the impeller turn the drive shaft in the direction of motor rotation ( clockwise} while applying light downward pressure on the housing. You never want to turn the fins tin the opposite direction of normal motor rotation. As for the muffs, I have never found a pair that seem to fit my motor very well, i use a very large plastic tote with water filled up past the water pickup on the lower unit and i do get water out of my motor when idleing on that setup. I also installed a tell tale on my motor, just a small piece of eigth inch hose hooked to the same eigth npt in the thermostat housing and another eigth inch adapter screwed into backside of cowling support.

 

[novicetech]

Re: 75 HP water pressure guage?

Steve you can get the impeller at your local mercury dealer, part number is 47-F84065.

 

[novicetech]

Re: 75 HP water pressure guage?

steve, try this for parts www.mercruiserparts.com, I think i may have given you the wrong part number although they are constantly changing their numbers.

 

[DC698]

Re: 75 HP water pressure guage?

Steve, Also, before removing the lower unit, you will have to remove a cotter pin from the shift rod mechanism to be able to slide the lower unit off. It's located below the cowling on the transom side of the motor leg. Be careful when reinstalling the lower unit that the shift rod and lower unit line up correctly and that the water pick up tube stays in.

 

[coktoastin]

Re: 75 HP water pressure guage?

Novicetech and DC698, thanks agian for the info and detailed replys! I'm going to begin the tear down first thing tomorrow (tuesday) morning, and it's nice to have some guidance before I begin. Being somewhat of a handyman, but new to the world of outboards, it's nice to have folks such as yourselves that are willing to offer some direction.<br /><br />Since I have no maintenance history on the engine, even if the impeller isn't the problem, I figure it will be a good place to start...<br /><br />Thanks again!<br />-Steve

 

[Realgun]

Re: 75 HP water pressure guage?

This might be of assistance

 

[chuckz]

Re: 75 HP water pressure guage?

Don't replace just the impellor. Buy the water pump rebuild kit.<br /><br />You should repair the temperature alarm and install a separate water temperature or pressure gauge if you like. One side of the alarm horn connects to the orange wire, the other side to +12VDC.<br /><br />Personnaly, I prefer the water pressure gauge. I think it lets me keep track of the health of my water pump better than temperature.<br /><br />The reason for both the alarm and a gauge, you're not always looking at your gauges. If the engine overheats the audible alarm lets you shut it down before damage occurs.

 

[coktoastin]

Re: 75 HP water pressure guage?

Realgun, thanks for the parts link. It has some good info and prices. <br /><br />L.I. Chuck, I will take your advice on the pump kit. Again, not nowing the maintenance history, I figure better safe than sorry. Also, I'm going to go with the temp alarm and water pressure guage combo. I like the idea of monitoring the water pump health as well as having an audible signal. Thanks for the advice! -Steve

 

[Realgun]

Re: 75 HP water pressure guage?

Realgun, thanks for the parts link. It has some good info and prices

While iBoats has a lotta parts and good prices they don't have the low volume or old stuff availible.