Water Pressure Gauge Questions - Older Johnson O/B

[Pmccraney]

Quick couple of question for you outboard pros:

For reference, I am working on a 1974 Johnson 85 h/p; Model No. 85ESL74B. I have the original OEM service manual.

I have done a fair amount of searching, but I am posting a thread to try and get a little more guidance. This boat came without any gauges hooked up. Since I will be installing a new water pump and impeller this winter, I would like to install a water pressure gauge so I can get the readings on a new impeller and be able to monitor things better going forward. I'd also like to install a water temp gauge.

1. On the water pressure gauge: I have read several threads that say to tie the pressure tester into your tell-tale line. The problem: this older o/b doesn't have the tell tale. I think from reading the shop manual and watching it run on muffs (when I bought it) that water recirculates until the engine reaches operating temperature and then the T-stat opens and some water bleeds out the exhaust ports on the back of the engine (but its not a spray like the pee line from a tell tale)... So, any guidance where to install the pressure fitting on this type of outboard?

2. On the water temp: The manual says that there is a buzzer switch in the remote that will indicate excessive engine temps. However, I'd still like to have a gauge. Any guidance on where to attach the sender would be most appreciated...

Thanks very much for helping me out!!

P.S. I posted THIS THREAD when I acquired my project boat last summer... You guys were a big help with some of the initial check up.... (the boat restore is going well so far).

 

[emdsapmgr]

Re: Water Pressure Gauge Questions - Older Johnson O/B

Since your engine was made prior to the telltale (came out in 78,) you have a couple of options on the water pressure. You can drill out the rear exhaust cover and thread it for a nylon hose barb, similar to the ones the factory used. Or, you can locate a 1978-newer used rear (outer) exhaust cover from a later flatback crossflow and just replace the cover. You should find nearly any marine salvage shop may have on of these covers-they are very, very common. The overheat warning system on the engine will not provide the correct signal for a temp gauge. Teleflex makes a wide range of inexpensive marine temp gauges and senders which will work on that engine. You'll need one of each. You'll have to fabricate a "Z" bracket to hold the tip of the sender flat against one of the heads. It's not sold with the sender. Make sure the sender and gauge are compatible with each other. The hot horn will sound when the cyl head temp gets to 212 degrees, so you will need a gauge that will typically measure from 100 to 250 degrees. 143-155 degress is "normal."

 

[Pmccraney]

Re: Water Pressure Gauge Questions - Older Johnson O/B

Many thanks Emdsapmgr! That is very helpful info.

 

[jasoutside]

Re: Water Pressure Gauge Questions - Older Johnson O/B

Any guidance on where to attach the sender would be most appreciated...

Hey broham, here's where I bolted mine on...

 

[Pmccraney]

Re: Water Pressure Gauge Questions - Older Johnson O/B

Thanks Jas; Exactly what I needed to see. Did you fab up that z clip to hold the temp sender flush to the head, or did it come with the unit?

 

[jasoutside]

Re: Water Pressure Gauge Questions - Older Johnson O/B

Nah, came with the sensor, piece of cake to install:eagerness:

 

[orbanp]

Re: Water Pressure Gauge Questions - Older Johnson O/B

Nice boat!
I would rather have temp gauge (possibly for each bank) than a water pressure gauge. You need water flow to remove heat from the block.
Granted, if there is no water pressure then there is possibly no water flow, but, if there is water pressure, the water passages could still be partially blocked, resulting in overheat.

Good luck, Peter

 

[Silvertip]

Re: Water Pressure Gauge Questions - Older Johnson O/B

Nice boat!
I would rather have temp gauge (possibly for each bank) than a water pressure gauge. You need water flow to remove heat from the block.
Granted, if there is no water pressure then there is possibly no water flow, but, if there is water pressure, the water passages could still be partially blocked, resulting in overheat.

Good luck, Peter

Water pressure gauges do not indicate whether the engine is overheating or not. They merely tell you how well the pump is working. Engines overheat for a multitude of reasons, most of which are not related to water flow. Timing advance and lean fuel mixture issues, bad thermostats and bypass valves top the list. Then there are the manufacturer specific issues like the diverters in some JohnnyRudes. So both instruments are essential if you really want to keep an eye on things. But then one needs to actually take a look at the gauges once in awhile.

 

[Pmccraney]

Re: Water Pressure Gauge Questions - Older Johnson O/B

Engines overheat for a multitude of reasons, most of which are not related to water flow...... So both instruments are essential if you really want to keep an eye on things. But then one needs to actually take a look at the gauges once in awhile.

Yeah, I was originally going to do a temp gauge only. Out of ignorance, a pressure gauge wasn't even on my radar screen. Then I read some stuff that Silvertip and others had posted (similar to the above) and decided I would try to install both if at all possible. My engine is old, but its a runner, and anything I can do to monitor her health (within economic reason), I'm game for...

So, temp sensor gauge looks easy/no brainer to install given the simplicity and piece of mind. Now, back to the pressure gauge for a sec:

Since your engine was made prior to the telltale (came out in 78,) you have a couple of options on the water pressure. You can drill out the rear exhaust cover and thread it for a nylon hose barb, similar to the ones the factory used. Or, you can locate a 1978-newer used rear (outer) exhaust cover from a later flatback crossflow and just replace the cover. You should find nearly any marine salvage shop may have on of these covers-they are very, very common.

Sounds like I have to drill into my outer exhaust plate or swap one out from a new model from the tell-tale years. Sounds a little more involved. Think I need to do some more reading before I tackle that one...

 

[phillnjack2]

Re: Water Pressure Gauge Questions - Older Johnson O/B

It seems a lot of people are relying on water temp guages that are t-in the the tell tale pipe.

well this is no good at all realy, as the tell tale will not let you know if water is getting round the engine.
Most tell tales ive come across are fitted to the exhaust where the water goes first !!!!!!!!!!!!
on my 3 cylinder the water enters the exhaust before it goes to the cylinders and the tell tale pipe comes
from the top of the side exhaust.
so ok i have water pumping up the pipe and into the exhaust then out the tell tale, but this has not told me
the engine is getting water around the head !!!!!!!!
the water pressure guage is the same as tell tale, very misleading, ive heard many people say i know ive got
water going round the engine because the tell tale is very strong...........
very strong can mean no water getting to the head/heads, in can mean the engine has a blockage and the
pressure is building up in the exhaust housing and its gonna give false impressions.
Head temp has got to be the safest way to go, just fit the sender high up like in photo above,its gonna be
more accurate than pressure guage unless you can be 100% sure your waterways have no blockages in them !!!!!!!!!!

we never see water pressure guages on cars ???????? but we always see temp guage, it realy the only way to be sure.
if you like a gadget then fit both.


phill