Engine Instrument Sending Units

[BMILLER]

For dual station, twin 318's. Are the engine water temp and oil pressure senders something special or will auto senders work? Have oil pressure on port engine running over 65 psi...closer to 80 at both stations. Strbd is at 65 cold, 45 at normal temp. Wondering if I need to replace the sender?

[prowlersfish]

You need to use Dual station senders ( not automotive) Not abnormal for 2 engines to read differently and oil pressure will be higher cold . Best to check with a mechanical gage to see if you have a gage issue .

the sender must match the gage too the wrong one not matching or singe station will throw of the reading

try swapping the senders

[BMILLER]

Are there any "universal fit" sending units? The instruments are original Trojan. I'll be changing them out sometime in the future to new Teleflex or Faria...........not certain which ones yet. Or perhaps Harkin Marine gauges....their website lists a five gauge set for a resaonable price and I'll eventually need 4 sets. They state 240/33 senders (?).........which is Greek to me.

[Big D]

Like Paul said, the hardware resistances must match. The 240/33 you mentioned is a typical resistance for a fuel sending unit for example. So you must use a gauge that is designed to operate with those resistances. There are a few standard ranges but you must ensure the gauge manufacturer you choose uses the resistances of the senders already on board or you'll need to get new ones. I'm pretty sure Faria and Teleflex use the same standards but check on their web sites. If I recall, VDO for example use different resistances. Also different standards for applications that originated in Europe. And don't forget the dual station application as Paul said, very important if buying new senders. Don't recall what gauges were used on your application, perhaps someone can chime in for that.

Before buying new senders, there is one more thing you should check; probably not an issue for your vintage but check to see if the senders have one or two contacts...also very import. If two contacts, get back to us.

[summer storm]

You need to use Dual station senders ( not automotive) Not abnormal for 2 engines to read differently and oil pressure will be higher cold . Best to check with a mechanical gage to see if you have a gage issue .

the sender must match the gage too the wrong one not matching or singe station will throw of the reading

try swapping the senders

Paul, my starboard temp gauge runs about 15 degrees hotter than my port at the lower station. This was checked with a handheld temp meter so I know it's not the engine. Would that be normal?

The only other thing is I 'think" it show the correct temp if the alt is not charging, but I am not 100% on that one.

[prowlersfish]

Thats a fair difference I would check all the grounds , could be a difference in the senders or the gages it self one could be slightly low and the other slightly high so a slight a difference can lead to a big difference , How do they compared to the heat gun ? heat guns read slightly lower then engine coolant temp due to surface heat loss .

what do the uper helm gages read ?

[BMILLER]

What has caused the concern is a local "marine service center" told me 65-80 psi on any Chrysler 318 is way too high. My concern, am I going to blow an oil filter or do I have a blockage somewhere that's causing the high pressure. According to the service records, the engine had a head gasket replaced about 2 yrs ago, so I don't know how long these 2 port gages have been reding "high" compared to starboard.

[Big D]

Normal for 318 is 45-60, up to 80 at 3000 rpm. If you're getting that high at idle, I would confirm pressure with a mechanical gauge at the engine or do as Paul suggested earlier and swap senders to see if the reading follows the swap. If not, return the senders to original location then swap the gauges or just the sender wire at the gauges and try again. The higher pressure you're reading is within limits as noted above for higher rpm so I wouldn't worry about the filter. But if that's your pressure at idle, I wouldn't want to sublect that filter to anything higher until it's resolved.

[summer storm]

Thats a fair difference I would check all the grounds , could be a difference in the senders or the gages it self one could be slightly low and the other slightly high so a slight a difference can lead to a big difference , How do they compared to the heat gun ? heat guns read slightly lower then engine coolant temp due to surface heat loss .

what do the uper helm gages read ?

checked today, it turns out the starboard gauge is very close +/- 3 and the port is low by about 10 degrees. That also means that the bridge gauges which I thought were close are now low by about 10 degrees.

I think it's got to be a ground.

[alexander38]

Thats a fair difference I would check all the grounds , could be a difference in the senders or the gages it self one could be slightly low and the other slightly high so a slight a difference can lead to a big difference , How do they compared to the heat gun ? heat guns read slightly lower then engine coolant temp due to surface heat loss .

what do the uper helm gages read ?

checked today, it turns out the starboard gauge is very close +/- 3 and the port is low by about 10 degrees. That also means that the bridge gauges which I thought were close are now low by about 10 degrees.

I think it's got to be a ground.

What Paul lead you to happens a lot in our older boats, what you find in your temps now are a norm for me my stbd engine runs 10 degrees hotter all the time but is fine on a temp gun +/- 5 from port I've come to except it as the norm...And don't worry about unless I get a spike in the readings, I do check all the hot spots with a temp gun after the engines are up to temp..
I too have found bad grounds and hot leads, seems Carver saved some money by not using tinned wire on everything

[rossjo]

Temp gauges work on resistance (thermistor). The resistance is:

• > high at low temperatures and
  > low at high temperatures.

In the example given earlier: 240/33 means the resistance at low and high temperatures:

• 240ohms resistance at Low temp (<80 deg F?)
  33ohms resistance at High temp (>=212 deg F?)

So, we have 3 Temp Gauges Troubleshooting Tips:

• 1) BAD WIRING FROM SENDER or TO BATTERY (corroded or bad corrections) will increase resistance and make the gauge Read Low (Not High).
  2) A BAD GAUGE GROUND will make the gauge Read High.
  3) After ruling out wiring, a bad sender or gauges can cause either effect.

As Big D stated earlier, it is important that the gauges and sender are matched. Different manufacturers should not be mixed (might work, but you have to check the resistance ranges).

When my upper gauges starting reading high, I added some small resistors (don't remember sizes, just experimented until all read right) to bring the readings back down. That worked for a year or so, and now the stbd gauges are high again. (I bought new gauges and sending units, but haven't installed yet, but that's another story).

[summer storm]

Well I'm glad I'm not the only one with this problem. It was driving me crazy trying to get all 4 gauges to read correctly. Now I am wondering if my alarms will work at the right temp.

Here are my temps after 15 minutes at fast idle, seawater temp 65 degrees. Temp taken at the thermostat housing

Port gauge about 155


Starboard gauge about 170

[rossjo]

Doug,

I think its probably one of the most common problems we Trojan owners have.

Good thread here ...

If you're reading low, the most likely culprit is the gauge ground.

[TADTOOMUCH]

Make sure nobody put teflon tape on the sending units. They must be installed without any compound or tape on them. You can take them out and see if they have the proper resistance at various temps based on the resistance values given. That will tell you if it is the sender or wiring or ground issues.

[rossjo]

Teflon Tape on the sending unit increases resistance, thus making the gauge read LOW.

If you gauges are reading HIGH, then you have a bad ground on the gauges, or your gauges or sender have gone bad. Its typically the ground wire.