Gauge Issues

[salfd]

I hope this is correct place to post this problem. here goes..
My second season with this. I Installed two Crusader 270 engines in my boat - they were 3 years old and run very good. The boat itself is a 1972 28' Scotty Craft.
Anyway - the boat needed a new set of gauges Oil and Water - Both Stations. I purchased 2 sets of gauges and sending units - ALL Teleflex - Matching - from the same Marine Supplier ( Jersey Shore ) and 2 new Thermostats.

Running both engines - the starboard engine appears to be ok showing 180 deg water and 50-60 psi oil on both stations - bridge and lower helm. The water temp is closer to 165 using a laser temp gun - I'll accept the 180 For Now on that engine.

The Port engine reads just a bit over 120 deg. water and 20-30 psi oil !! on both sets of gauges upper and lower !! This is not correct or acceptable.

After trying all the testing suggested by Teleflex Tech and a bunch of other sources - I got nowhere !! I even ran dedicated wiring from the senders to each gauge and each station - completely bypassing the boat's wiring harness. Still getting very low incorrect readings on port engine. All things point to incorrect senders although they were purchased matched to gauges and verified packaging said DUAL STATION. I even went back to the marine shop - purchased another water sender - SAME results.

There are the Teleflex 1/2 inch NPT thread and installed on the manifold plug close to the thermostat housing on this engine. The Oil gauge is on a tee with thelow pressure alarm.

I experimented a little and found that if I remove one set of gauges from either the bridge or the lower helm - THEN the one set still hooked up reads the same as the starboard gauges - around 180 deg water and 50-60 psi which is very close to actual.

My question is - other than install a second Temp sender ( there is a spot I can use but can't find one for second OIL gauge ) has anyone else run into this and how did you resolve it. Could it be that the senders I am buying are actually SINGLE station !!???

Teleflex Tech gave up on this. Can anyone out there help ??

 

[flargin]

Re: Gauge Issues

have you researched a bad ground?

 

[Silvertip]

Re: Gauge Issues

You can install a "T" fitting in the port that the current oil pressure sender is installed in. Then install both senders into the "T". Use a very short nipple to connect the port to the "T". This will reduce the possibility of vibration breaking a long nipple. Senders are resistance elements. Putting them in parallel upsets the electrical characteristics of the circuits (two 250 ohm resistors in parallel for example results in a circuit resistance of 125 ohms). Do you have a separate gauge for each engine at both stations (four gauges total). You either have both gauges paralleled or the sender you have is not a dual station. Check it with an ohmmeter.

 

[salfd]

Re: Gauge Issues

I did hook up a new ground wire to each gauge. this didn't change anything.

I purchased all new gauges and all new senders for these engines. Each engine has full set of gauges for lower helm and bridge. 2 oil and 2 water temp etc. for Port engine - same for Starboard. They were installed in place of the old gauges wire for wire. I wanted to start off with correct matching New gauges/Senders when I repowered the boat.

I've been wrestling with this for some time on and off. It is frustrating - I even tried a new water and oil sender - thinking it had to be a sender issue. I checked with an ohm meter at the senders - I am getting very close readings on both engines in the 50 ohm range for the water and about the same for oil. According to Teleflex diagram - those readings should be around 120 ohms for dual st. senders !! confusing me even more - the gauges should show 240 degrees water and 80 PSI oil - FULL READINGS - but don't. I did the tests on the gauges and they seem fine.
It's when I hook up the port engine's gauges to their senders - I am getting about half the readings I should get which does seem to fit with your parallel resistance explanation. If worse come to worse - I will install the T fitting for 2 oil senders and I do have 2 spots where temp senders can fit - at least I'll know how that engine is running from either station.

What is making me crazy is that I bypassed all the harnesses and ran dedicated wires to the both stations - and change senders a couple times - Although what you say makes sense - nothing is making sense.

I'll go one more time - check wire for wire - connection with connection - if all fails to reveal the problem - separate senders - for each gauge !

 

[Silvertip]

Re: Gauge Issues

Using your resistance meansurements it is obvious you have a parallel issue either at the gauges or the senders. Paralleling the gauges results in the same resistance issue that paralleling the senders creates. Disconnect the wires from the sender. Measure resistance from each of the two terminals to the engine block. They should be the same. If not, you do not have dual station sender or the sender itself is defective. If the sender is defective and you got the replacement from the same source, an entire batch could be defective. It has been known to happen.

Back to basics here: With the key ON (not RUN), measure voltage on the "I" terminal on the gauge. Should measue battery voltage. If not, there is a wiring issue. This terminal is the 12 volt feed for all gauges.

Disconnect the wire at the "S" (sender) terminal on the gauge in both stations. Measure resistance to ground and repeat at the other station. This reading should be the same as when you measured the sender. If not, you have a wiring issue. Use a known good ground reference -- such as the ground bus -- not the ground terminal on the gauge.

Lastly, measure resistance from the ground terminal on the gauge to that same known good ground reference. If the ground is sound that part of the circuit is ok.

 

[salfd]

Re: Gauge Issues

Guys - I believe we can close this out ! I disconnected all the harness connections for both engines and both stations. I wire-brushed the terminals male and female until then were clean and shinny. Then I traced all the wires are made sure their connections were clean. The boat is old and had a lot of wiring that went "no-where" so I got ridof all the dead stuff. In short. Except for one small glitch with the upper gauge lights - the temp gauges are reading 160 degrees and the oil is at 40 psi - so - I have to say that all the hard work and testing, at answers from this forum all payed off.

Thank you all - we can put this one to bed!

Sal

 

[flargin]

Re: Gauge Issues

Guys - I believe we can close this out ! I disconnected all the harness connections for both engines and both stations. I wire-brushed the terminals male and female until then were clean and shinny. Then I traced all the wires are made sure their connections were clean. The boat is old and had a lot of wiring that went "no-where" so I got ridof all the dead stuff. In short. Except for one small glitch with the upper gauge lights - the temp gauges are reading 160 degrees and the oil is at 40 psi - so - I have to say that all the hard work and testing, at answers from this forum all payed off.

Thank you all - we can put this one to bed!

Sal

Sal,
Great to hear.

It is nice to hear the solution, because someone will search for the problem and be able to see the answer as well!