Mystery Gauges

[snook91901]

The PO of my boat collected various odds and ends during the years he was planning on fixing her up himself. I am grateful that all of these things came with the boat at purchase (new teak handrails and tiller, ground tackle, replacement fuel tank, spare carb...etc), but some have been a little confusing or not suitable for my boat (set of wooden spreaders not even close to the correct size). Among these things is a rather handsome instrument panel with tach, ammeter, oil pressure and temperature gauges.

Knowing that some sending unit/gauge pairs use different resistance at the sending unit for a given oil pressure/temperature, is there any way to identify an appropriate sending unit for these gauges, or at least to identify the gauges themselves in order to order the appropriate senders?

[jpian0923]

Can you post a pic?

[Dave Neptune]

Snook, are there no names on the gages or panel? If you can identify the "brand" you should be able to find the info on line.
Per jpian post a pic if you can, perhaps someone could identify them.

Dave Neptune

[snook91901]

There is no brand information on the gauges. I'll post a pic soon.

I suppose I could go buy a set of cheap resistors and test the readings on the gauges with simulated resistances from the "sending unit." 33 ohms at 0psi, 230 ohms at 80, for example. That just sounds like more work than I want to do

[snook91901]

After deciding to just scrap the old gauges (never could get them to work) I tried to remove the temp sending unit, but she wouldn't budge, even with the breaker bar and penetrating oil. I suppose I could probably put more force on it, but I was wary of damaging the head. Drilling the sending unit out does not seem fun, so now I am left with using it as is and finding the matching gauge.

The resistance at about 70F was around 2.5 K ohms and this decreased to 500 ohms around operating temp. Can anybody help me guess at a gauge brand? I've spent countless hours trying to match these resistances to gauges online to no avail.

Alternatively, is there any other reliable way to keep an eye on engine temp? Other places to install temp sending unit? Surface temp readings? Oil temp readings? Sticking my hand on the block?

[jpian0923]

Did you try heating the unit before removing it? Mine was hard to get out too.

[Marty Levenson]

Couldn't you leave it as is, and install a tee fitting where the hot water enters or exits the manifold? Then put a new sensor in one side of the tee....?

-Marty

[snook91901]

JPian-
I tried it with a hot engine. I will try with cold or cooling engine next time I'm down there.

Marty-
good idea. Would that water be roughly the same temp as the water going across the original temp sender location? I would imagine if there is a lot of water going through the bypass loop it would give falsely low temperatures.

[jhwelch]

I'd try the T solution too. You don't need to have the T location match the temperature range you get where the current sensor is. You are interested to know if there is some departure from "normal" numbers. Once you have the T installed you will get some experience what those "normal" numbers are and then can watch for overheating.

-Jonathan

[hanleyclifford]

http://www.moyermarine.com/forums/pi...tureid=826Here is one suggestion.

[jpian0923]

or,

http://www.moyermarine.com/cgi-bin/s...rebuilder.html

[Marian Claire]

Alternatively, is there any other reliable way to keep an eye on engine temp? Other places to install temp sending unit? Surface temp readings? Oil temp readings? Sticking my hand on the block?
I have my temp sensor in a T where the water exits the manifold as suggested earlier. I also have a simple oven thermometer sitting on the head, the base is wedged between the head and manifold. Both give very consistent reading but the oven therm is about 20 deg higher. Pics in profile A-4 album. Dan S/V Marian Claire

[Jesse Delanoy]

Snook, I had a temp sending gauge that wouldn't budge, too. I wore off all the edges on the hex bezel trying to get it out, until it was perfectly round. I had a new gauge and sending unit ready to install, but just couldn't get the old unit out.

One day, when I'd been working on the engine and it was nice and hot, I took my biggest vice grip, clamped it on the sending unit as tightly as I could, and gave it a couple of whacks with a rubber mallet (remember -- righty-tighty, lefty loosey!!!). That loosened it, and it came out like a dream.

If you still have hex edges on yours, you should be able to do the same thing with a socket wrench. Just start tapping on the wrench handle, gradually increasing the force. It should work.

[snook91901]

I'll try again to remove the old sending unit, although it is a shame because it works fine.

My concern with installing a sending unit in an alternative location is that the engine I am working with sat out in the rain for years before I began resuscitating her. I've no idea if the current normal operating temp is overheating or not. Also, I have pretty low flow through the cooling system so I need a way to check if it is sufficient or not. Maybe I'll buy an infrared thermometer and measure the engine surface temp directly in a few spots to get an idea that she's not overheating, then I'll install a sending unit between the thermostat housing and the manifold.

Can anybody give me an idea how hot the surface of the engine should be in a few locations? I've read on a few threads that the head temps can vary greatly depending on the flow around the head and this isn't as much as a concern as block temps. Is this true?

[roadnsky]

Originally Posted by snook91901

Can anybody give me an idea how hot the surface of the engine should be in a few locations? I've read on a few threads that the head temps can vary greatly depending on the flow around the head and this isn't as much as a concern as block temps. Is this true?

At fully warmed up running temp, my cockpit Temp Gauge reading at 170°...
my laser temp readings of the head and block vary from 140° to 200°

The UHS and around the plugs are always the hotter readings.

[JOHN COOKSON]

Don't use a open end wrench when you remove the temp sending unit. It will only round the soft brass.
I had good luck with a closed end wrench and a hammer.
The best bet is vibration + heat from a running engine + a closed end wrench + a hammer. If the sending unit hex is rounded you'll have to use a pipe wrench or vice grips or some other method.
My personal perference is a flat hand wrench rather than a socket to loosen stuff because I have a better feel with a wrench.

TRUE GRIT

[Loki9]

Use a 6-point box wrench or socket, not 12-point. An impact wrench might help.

Or, leave the sender in place and hook up a temp gauge to it. It might work alright, and if not you were going to remove that sensor anyway.

[snook91901]

How much of a risk to the head is there in taking a breaker bar/using an impact driver on the sending unit? Can I really wrench on the thing, or will I wind up cracking the head, damaging head gasket and so on?

Also, any suggestions for a surface temperature sensor to attach directly to head or old sending unit?

[Loki9]

Cracking the head is unlikely, but there is always a risk. More likely, if it doesn't come loose, is that you'll round the corners off the sending unit and be forced to drill it out.

On mine, the sending unit is threaded into a brass reducing bushing to change it from 3/8" NPT to 1/2" NPT (or 1/2 to 3/4 I forget). Is yours similar? If so, you have two options to unscrew it, either unscrewing the sender from the bushing or the bushing from the head. I'd guess it might be easier to get the sender out of the bushing, if you haven't tried that already.

Again, are you sure you need to remove it?

[JOHN COOKSON]

Originally Posted by snook91901

I'll try again to remove the old sending unit, although it is a shame because it works fine.
I've no idea if the current normal operating temp is overheating or not. Also, I have pretty low flow through the cooling system so I need a way to check if it is sufficient or not.

When I removed my temp sensor unit after many years of service here's what I found: The sensor was coated with some kind of white minerals. I was able to remove this grunge with a tooth brush and lime away.The port where the sensor sat was full of crud. I was able to ream this out so I got good water flow past the sensor. I doubt that my temp readings were very accurate. It also made me realize I was past due for an acid flush.

While I had the sensor out I put a 6" nipple (fun to type that) in the sensor hole, attach a tube to it and clamp the tube. Next I started the engine and ran it untill the thermostat was open, clamped the bypass hose and unclamped the hose on the nipple. I was able to flush quite a bit of crud out of the engine by doing this.

TRUE GRIT

[snook91901]

Loki -

My sending unit is threaded directly into the block, with no reducing bushing. I'm not totally sure I want to remove it, but I need some place to sense engine temps that is actually reflective of whether the engine is overheating or not.
Alternatively, if I can get an idea of what normal surface temps are with my ir thermometer and compare them to observations from people in the a4 community, I'll get an idea of what healthy temp readings from an alternate location (T in the hose between thermostat housing and manifold for instance) should be. This way, I'll have some way to monitor for overheating during normal operation, without having to remove the sending unit. So please keep those readings coming and thanks to roadnsky.

I should also mention, that my thermostat housing is highly corroded. I can not use a thermostat, instead I have check valve/ball valve combo in the bypass.

[snook91901]

I have found this thread with some temp readings
http://www.moyermarine.com/forums/sh...d+thermometer?

Seems like anywhere on the head, except right next to the plug, 140-200 is a pretty safe range.

[Loki9]

You need to get your motor cleaned out and cooling/running well. Then you'll learn what the "normal" temp rang on your gauge is. You don't need to have exact accurate numbers, just a normal range. Most temp gauges found in cars just read "L" to "H" and that's really all you need.

I have two temp senders on my A4. There's one in the head that feeds an over-temp alarm. There's a second in a tee where the coolant exits the manifold that feeds the temp gauge in the cockpit (reads 180 normally).

[Marty Levenson]

I think in your shoes I might set up the alternate sensor in a tee somewhere off the head, as described in other posts, without connecting the wire. Leave your original sensor hooked up, run the engine to fully warmed up, in gear, and note the temp reading through your old sensor. Then switch the lead over to your new sensor and compare. Voila: you have the info you need to know what reading you want on the new sensor.

I think sooner or later you will want to be using a sensor you can remove and replace.

I hope that's a useful thought!

-Marty

[edwardc]

Originally Posted by Loki9

...I have two temp senders on my A4. There's one in the head that feeds an over-temp alarm. There's a second in a tee where the coolant exits the manifold that feeds the temp gauge in the cockpit (reads 180 normally).

Interesting... I have just the opposite. The sensor in the head feeds the gauge, and the one on the tee in the manifold's water outlet feeds the overtemp alarm. The gauge runs steady at 180 under load, with fresh water cooling.

For what it's worth, using a heat gun and an infra-red thermometer, I determined that my overtemp sensor closes at 200 deg F. I've found that if I shut the engine down after reaching steady running temp without idleing for a minute, the overtemp alarm will go off as the latent heat in the engine quickly raises the coolant temperature. On the other hand, if I idle in neutral for a minute, the engine cools ( as indicated by the gauge dropping from 180 down to 160), then I get no alarm after stopping.

(Note: the alarm only actually happens when I switch the ignition back on, as its wired thru the ignition power).