3000 (gas) temperature gauge

[MJMJ]

The temp gauge on my 70 3000 hasnt worked since I split and took it apart for new core plugs and head gasket two years ago. Always worked before that, so I assume I missed something putting it all back together.
Ive tested a few basic things, but not sure what to check next. I have continuity from sending unit to gauge. The fuel gauge works (sort of) so I unplugged the wire from the fuel gauge and plugged it to the temp gauge and the temp gauge worked. I have a box of sending units and have tried four, so Im confident theyre not all bad. What would be the next obvious thing to check? Thanks.

 

[Sean in PA]

Check for continuity from the head near the sending unit to the negative battery terminal. When you replaced the head gasket you could have isolated the head electrically from the rest of the engine.

 

[johnofnewhaven]

I am no mechanic but how can
that be with head bolts going
into the block? Like I said I am
no mechanic.

 

[Sean in PA]

I'm not sure exactly how it could have happened. You could have painted the outside of the head while you had it off and the overspray could have gotten under where the heads of bolts ride, thus insulating the head from the rest of the engine. Or you could have used a thread lock compound on the threads of the bolts which would insulate things, or it could be any of a number of other possibilities. I wasn't there when you did it.

No need to be a mechanic, or even need to understand how it might happen. Just measure for continuity. It's a simple thing to do. If my guess is wrong then you'll know for sure and it won't cost you anything more than a couple minutes of your time. Arguing back and forth on an internet forum can waste days due to various folks' schedules and the resulting delay in response times. If it is the issue then it's a simple fix to add a ground strap from the head to the block.

If you want to think that you're learning more, measure the resistance from the terminal on the sender to the negative post on the battery, first when the engine is cold, and then several times as the engine warms up to operating temperature.

 

[MJMJ]

Um, I think it was more of a question than arguing, but either way it wasnt me asking. I did go ahead and check, theres good continuity from head to ground.

 

[gears]

Seans got a good point; people post a question, we suggest possibilities without being there to see or test and sometimes the ensuing discussion looks like an argument.

I always ask in case someone has has a similar issue and found a quick solution I didnt think of, stumble across or actually troubleshoot and solve.

We need to read responses with our need in mind rather than our hackles raised looking for a fight.

 

[sotxbill]

also guessing..

if you ground the wire at the sensor wire on the front of the engine, the gauge should move to full hot.... if not...

The sensor wire got pinched, cut, damaged so it no longer conducts electricity?

the plug between the engine and the gauges needs to be pulled apart and cleaned with a contact cleaner and rejoined??

the ground wire on the instrument cluster is bad??

you got the wrong wire on the heat gauge?

Your voltage chopper thingy on the back of the instrument panel is bad or hooked up wrong.... as it affects only the gauges?

the 3 amp fuse is blown and nothing works other than the mechanical tach (assuming it was working)...

the power wire pulled off the key switch and the power to the gauge?

sensor bad?

Key bad?

battery bad?

battery cables bad?

moved to alternate universe where the gauges and sensors are reversed?

whoa... I need some coffee...

 

[johnofnewhaven]

Sean didn't even read who posted
the question and immediately
said it was an argument. Thats
BS!!! I asked the question. It
was just a simple question to
try to learn something. Even the
original poster said it was a
question not an argument. Sean
should of read who sent what
before he got all upset. Even
then it was a simple question
not an argument!!! No one was
looking for a fight.

 

[Sean in PA]

(quoted from post at 08:32:09 06/07/20) Sean didn't even read who posted
the question and immediately
said it was an argument. Thats
BS!!! I asked the question. It
was just a simple question to
try to learn something. Even the
original poster said it was a
question not an argument. Sean
should of read who sent what
before he got all upset. Even
then it was a simple question
not an argument!!! No one was
looking for a fight.

Sorry if I hurt your feelings. As I said, I wasn't there when the work was done, so I could only guess as to why the head might be isolated electrically from the rest of the engine. or even if it was. That's why I suggested measuring to see. I have seen various vehicles over the years that came from the factory with ground straps from the head to the block, or from the engine to the transmission and/or frame because of issues with not all "ground points" being the same without them, sio that is why I asked.

Now back to the original poster:

I did go ahead and check, theres good continuity from head to ground.

What do you mean by "ground"? I specifically said to measure to the negative post of the battery.

 

[Sean in PA]

And sorry if my replies and suggestions seem gruff. I do computer support for a living, remotely, and I sometimes spend hours or days asking questions just to find out something that I could have figured out in minutes if I had been there in person because the person reporting the problem didn't think to mention something at the beginning because they either didn't notice it or didn't think it was important or worth mentioning.

Over the years I have found that asking all possible questions and asking for all possible remedies to be tried up front helps shorten the time to resolution, which is what most people are looking for in the long run. But even then, a vast majority of my customers seem to only read the first sentence of what I send them and therefore only answer one of multiple questions or try one of multiple suggestions.

So when I try to help someone out here I tend to follow the same methodology. It may seem rude to some, but it is effective. My customers always get an automated email requesting them to complete a survey after a case that they have opened has been completed, and I have never received a single negative score on any survey in over 20 years.

 

[MJMJ]

What do you mean by "ground"? I specifically said to measure to the negative post of the battery.

I mean the neg post on battery, bad terminology I guess.
I made some headway, but probably more confused now. Im sure its just my poor understanding of how it all works. I made a wire to run from sending unit to gauge, grounded the sending unit, heated the sending unit with a hair dryer, and the temp gauge worked. To me that would suggest either lack of continuity in wire harness or bad ground to head. Is that wrong?
I again check continuity in the harness from sending unit to gauge, and made sure the head is grounded. I know theres something Im missing, just not sure what.

 

[MJMJ]

Well, one more update. I plugged in another sending unit to the harness wire, grounded it to the neg post, and again heated it with a hair drier. The gauge worked again, so that leads me back to the sending unit I think? I tried this yesterday but probably didnt get a good ground to the sending unit.

 

[MJMJ]

Not the sending unit...

Im going to have to tap out for a while. When I test all the components individually, it all works. As soon as I screw the sending unit into the head, nothing. There has the be a flaw in my methods somewhere. Just not sure where.

 

[GB in MT.]

(quoted from post at 08:20:23 06/07/20) Well, one more update. I plugged in another sending unit to the harness wire, grounded it to the neg post, and again heated it with a hair drier. The gauge worked again, so that leads me back to the sending unit I think? I tried this yesterday but probably didnt get a good ground to the sending unit.

Take a small rat tail wire brush....stick it into the sender hole of the block, and clean the threds REALLY good.
Sounds like maybe the block threds are on again...off again with ground loss to the senders.

My sender was doing that and even with a NEW sender, it was not getting good ground. Once I cleaned the theds up going into the block, it was good ground, and have had no problems with it since!!!

Gary
:roll:

 

[MJMJ]

Ill give that a shot. It really does seem like the sending unit isnt grounded right. I ran a wire from sending unit to neg battery post to eliminate that, but maybe I didnt get good contact. Thanks

 

[MJMJ]

Well, the sending unit is grounded fine it seems. Im about out of ideas, Im all ears if anyone can think of something I may be missing.
Heres a possible dumb question. Is there any chance the sending unit isnt threaded into the head far enough, leaving a bubble of air trapped around the tip? Even then it seems the temp gauge should register something eventually, but Im grasping at straws.

 

[GB in MT.]

(quoted from post at 15:33:47 06/07/20) Well, the sending unit is grounded fine it seems. Im about out of ideas, Im all ears if anyone can think of something I may be missing.
Heres a possible dumb question. Is there any chance the sending unit isnt threaded into the head far enough, leaving a bubble of air trapped around the tip? Even then it seems the temp gauge should register something eventually, but Im grasping at straws.

Unless there is something blocking the sender port, from the inside of the head, you should have a steady stream of water/coolant, flowing from that opening, when you pull the sender out with the water jacket full of coolant.
Have you investigated the possibility of a bad thermostat????
Stuck thermostat, in the open position, may be open just far enough to keep the engine cool enough to not register anything
on the sender???

Gary :?:

 

[MJMJ]

Its worth checking. Ive run it long enough that I ASSumed it would be warm enough to register, but maybe not. Thanks for the idea.

 

[MJMJ]

Well, GB in MT. was correct. Frankly I feel rather stupid for wasting so much time on it when there's nothing wrong. I put in a new thermostat, brush hogged for a while, and the temp gage made it to the middle of the blue. I would expect it to be about centered between the red and blue. In the 30 years I've used this tractor, it's never run this cool. I cleaned out some crud in the block when I changed core plugs, and replaced my old radiator this winter. I never expected that sort of difference. Appreciate the help.

 

[GB in MT.]

(quoted from post at 09:31:52 06/09/20) Well, GB in MT. was correct. Frankly I feel rather stupid for wasting so much time on it when there's nothing wrong. I put in a new thermostat, brush hogged for a while, and the temp gage made it to the middle of the blue. I would expect it to be about centered between the red and blue. In the 30 years I've used this tractor, it's never run this cool. I cleaned out some crud in the block when I changed core plugs, and replaced my old radiator this winter. I never expected that sort of difference. Appreciate the help.

Glad to have helped you fig. it out. Also very glad to hear that you now have it working again.!!!
I have a '73' 3000 diesel That I have only had for not quite a yr, and when I saw your post....I thought maybe I could help someone else for a change!! BTDT, sort of thing, and on the very same problem that I went through.
You don't have a clue how many ??'s I have had to ask of the guys on this forum, just to keep this 3000 running!!



Again....Glad to hear you got it fixed!!!

Gary 8)