175 blackmax water pressure gauge

[tbird175]

I want to install a water pressure gauge on my 1978 175 HP V6. Where is the best place to install the sensor on the engine and what type gauge should I use? It now has a temperature switch for an alarm that is no good and I can not find a replacement for it.

 

[j_martin]

Re: 175 blackmax water pressure gauge

I want to install a water pressure gauge on my 1978 175 HP V6. Where is the best place to install the sensor on the engine and what type gauge should I use? It now has a temperature switch for an alarm that is no good and I can not find a replacement for it.

The OT switch should be an easy to get part, either OEM or aftermarket.

On top of the engine, just behind the flywheel, there is a pipe threaded hole with either a plug in it, or a hose going down to the poppet. That's where you install the gauge. There's a stock Mercury gauge, and many oem gauges, and they are all fine. Cost about 50 bucks.

hope it helps
john

 

[tbird175]

Re: 175 blackmax water pressure gauge

The OT switch should be an easy to get part, either OEM or aftermarket.

On top of the engine, just behind the flywheel, there is a pipe threaded hole with either a plug in it, or a hose going down to the poppet. That's where you install the gauge. There's a stock Mercury gauge, and many oem gauges, and they are all fine. Cost about 50 bucks.

hope it helps
john

Thanks for the help john. I have had no luck finding a replacement water temp switch. All the ones that are available are held in place with a bolted bracket or clamp. Mine is secured with a molded epoxy or simjlar material, no mechanical retainer. Even Mercury parts could not help me, their books do not go back far enough according to the tech that I talked with. Do you think that I will be safe using the pressure gauge instead of a the original temp alarm system?

thanks,
tom

 

[usskydvr]

Re: 175 blackmax water pressure gauge

the temp sender should be p/n 78799. also water press should be 5 PSI

 

[dezmond]

Re: 175 blackmax water pressure gauge

don't know why the tech would say that. Seloc even makes a manual for that motor.. I have a 1977 175 BlackMax I am working on now to install on my boat.. You should have no probs getting the temp sender like ussdydvr said

 

[tbird175]

Re: 175 blackmax water pressure gauge

the temp sender should be p/n 78799. also water press should be 5 PSI

Thanks, can you tell me how to replace the unit? There is no retainer clip. It appears to be cast in the hole in the head with epoxy or similar material.

 

[j_martin]

Re: 175 blackmax water pressure gauge

Thanks for the help john. I have had no luck finding a replacement water temp switch. All the ones that are available are held in place with a bolted bracket or clamp. Mine is secured with a molded epoxy or simjlar material, no mechanical retainer. Even Mercury parts could not help me, their books do not go back far enough according to the tech that I talked with. Do you think that I will be safe using the pressure gauge instead of a the original temp alarm system?

thanks,
tom

You don't run with your eye glued to the pressure gauge. If you wrap a plastic bag on your LU the alarm goes off in about 4 seconds at WOT. You have about another 4 to throttle down without damage. My alarm has saved my bacon a couple of times idling through mucky channels.

Get, or guess the temp specs and physical size of the switch. Find a klixon (tm) auto-reset switch to approximate it. (try mouser.com) Clean out the old one with a dremmel tool. solder 2 leads to the new one and glue it in place with jbweld or whatever you have laying around. A metal filled resin conducts heat better than a clear one. Wire one lead under the nearest ground screw, and the other to the alarm circuit.

Another option would be an electronic temp gauge with an alarm function. You will still have to find a way to mount a sensor.



hope it helps
john

 

[usskydvr]

Re: 175 blackmax water pressure gauge

Someone must have epoxied it in. It didn't come from the factory like that.
You will need to CAREFULLY grind it out. Rather than epoxy in the new one, I would try to make some sort of cover plate with a rubber gasket under it to hold the new on in place.

 

[tbird175]

Re: 175 blackmax water pressure gauge

Someone must have epoxied it in. It didn't come from the factory like that.
You will need to CAREFULLY grind it out. Rather than epoxy in the new one, I would try to make some sort of cover plate with a rubber gasket under it to hold the new on in place.

I bought the engine new myself in 78 and the switch has never been changed. I am very puzzled by this. I am supposed to meet with a mechanic tomorrow that has experience with the old mercs., hopefully he can help. I will post my findings.

 

[j_martin]

Re: 175 blackmax water pressure gauge

I bought the engine new myself in 78 and the switch has never been changed. I am very puzzled by this. I am supposed to meet with a mechanic tomorrow that has experience with the old mercs., hopefully he can help. I will post my findings.

If you look close, you may find a screw busted off flush near the switch. I must say I've never heard of one epoxied in either. It doesn't make any sense except as a baling wire fix.

At any rate, it shouldn't be hard to fix with parts that are available.

 

[tbird175]

Re: 175 blackmax water pressure gauge

At last, the "mystery" about my temp sensor has been solved. After several phone call to Mercury and e-mails, I received a call today from an experiened technician. On some of the older V-6 with two piece heads the sensors were installed without retainer clips. They were retained witrh a sealant. He told me how to get out and which sensor to order to replace it. He was very helpful and I now have more confidence in Mercury customer service. Thanks for all the comments.

 

[tbird175]

Re: 175 blackmax water pressure gauge

FYI Just got my camera working again. Here is a pic of the temp sensor that I have been talking about.

 

[usskydvr]

Re: 175 blackmax water pressure gauge

Good Deal. Learned something new today. So how did he tell you to get it out and what p/n did he give you?

 

[tbird175]

Re: 175 blackmax water pressure gauge

Good Deal. Learned something new today. So how did he tell you to get it out and what p/n did he give you?

You gave me the right part number(78799) in your previous post. He said to just prise the old one out, and push the new one in the hole. It is self sealing but is good to use some sealant to be sure like the factory did. I will try this as soon as I find a new one, he said that they are out of stock at the present time at Mercury. I am going to try some of other supply houses.

 

[usskydvr]

Re: 175 blackmax water pressure gauge

So the sealant was more like RTV Silicon than epoxy...correct?

 

[tbird175]

Re: 175 blackmax water pressure gauge

So the sealant was more like RTV Silicon than epoxy...correct?

Thats right, it is still flexible.