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temp needle stuck on being maxed out

E

equalizer

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Currently in Northern Alberta. Soon to be heading
Hey guys, I've finally decided to post my question after three days of frustration. My temp gauge starting going haywire last week (in addition to that hidious squealling), so I deicded to replace both the water pump and thermostat. Today, after getting both of those in, it continues to jerk back and forth quickly right at the start, but then after a few minutes, just staying on the maxed out right side...Funny thing is that when I left it idling for about five minutes with the rad cap off, nothing happened, it didn't seem to overheat as shooting coolent would indicate /forums/images/graemlins/smile.gif As well, the top rad hose doesn't seem to be getting any fluid right at the start, so I'm wondering if the water pump belt isn't tight enough or whether it takes a while for the top hose to have any fluid go through it....Anyway, its a 305 72 K5 and any help in identifing the problem would be great....Could be just the gauge itself but I don't want to be taking any changes if someone might have an idea of what I might have screwed up in my lastest fix it gig /forums/images/graemlins/thinking.gif
 
On the driver's side plugged into the cylinder head is the water temperature sender. It will have a single wire (green maybe? I forget) coming off it. Trace that wire and make sure it isn't grounding out on something. It goes down and follows along the spark plug wires to the back of the motor.
 
most likely some kind of wiring problem such as a bad ground in the dash...maybe /forums/images/graemlins/confused.gif
 
Here is what I would do... First, test the green wire with a voltmeter and find out if it's grounded or stripped anywhere! Second(or first cause it's probably the problem...) Change the sending unit that green wire is attached too! It will cost you about $5 and more than likely the spring in it is sprung! No preasure with the cap off means no reading... When you put the cap off, the gauge goes haywire! Sounds like the gauge is fine, but you have a short or a bad sending unit! /forums/images/graemlins/thumb.gif
 
For some reason that wire from the temp sensor is attracted to the header like flies on Sh$t.
 
dark green wire driver side front of engine and that sensor in the head there at front driver side is temp sensor yep and the wire is shorted out on metal somewhere if the temp guage needle is pegged over to hot, trace the wire(back to firewall wiring harness main plug) from the sending unit


in the 78 shorty out here that i put 250ci engine into the brake warnigng light comes on and the temp guage paegs over to hot when you step on the gas pedal with engine running,

anyone explain this phenomenom ?
i cant, but i thinks its pretty funny and interesting

hehe
 
Temp gauge stuck on max

I'm still trying to fix this broken gauge. Bought a new temp senser, put a new spade on the green gauge wire, made sure it looked ok. Replaced all the grounds at the battery going to the frame and the radiator support. Still nothing, the gauge is always maxed out, never twitches or anything. Someone said that it may be grounded out, so I unhooked the battery, and no change. If the gauge itself was working, when the battery is unhooked, shouldn't it return to the low reading?
 
Trace the wire going from the sender back to the gauges. They get brittle and ground out to practically anything.
 
Temp gauge stuck on max

But wouldn't unhooking the battery return it back to zero?
 
Not necessarily. Try the green wire first. If the gauge works and the sender works, then it is the path to get from the sender to the gauge.
 
temp gauge maxed out

Problem is I don't know if the gauge it good, bought it like that. Is there a quick way to tell if it will work?
 
temp gauge

Just a side note, none of the gauge lights work when the headlights are on. Could it be related? All the other gauges work fine, except for the fuel gauge, it kind of bounces around.
 
Then try pulling the cluster. It will give you a chance to test the gauge or replace it, and check the printed circuit board. Some of the connections get messed up after a while, because they are paper thin, and repeated removal or replacement messes them up. It sounds like a ground problem, but it would be easier to start by tracing that green wire to make sure that is good FIRST.​
 
Easy test of the wiring/gauge.

Pull the sender wire off with the key in run. The gauge should max out one direction. Now short that connector to ground. Should peg the other direction.

If it fails that test, you've definitely got a wiring or gauge issue, not sender.

You should be able to run a continuity test on the green wire to ground with the sender disconnected, and get nothing.

I agree, it's pretty likely in the printed circuit board or the gauge itself, but not a sure thing.
 
Thanks for all the advice, I've got access to another gauge cluster that I know was working, I'll see if it does the same thing and go from there.
 
Temp maxed out - found problem

This is one for the books. Got another gauge cluster from a diesel/no overdrive/with clock. Mine was different, so I thought I would just swap the temp gauge since I knew all the other gauges worked. Getting the cluster out found a lot of broken tabs, etc., evidence of tampering. No big deal, who know what they needed back there for. So I procede to take my cluster apart, pull the temp gauge, and see that some PO had wrapped up some plastic tape around one of the legs of the gauge. No amount of electricity was getting through that mess. Got it all back together (same gauge, just no tape this time) and sure enough, BINGO, gauge works. However after letting it sit running for awile, got it to edge up to about 240 before shutting it down. The engine that I thought probably needed a tuneup, has probably been royally cooked. I don't think the guy I bought it from knew this because of all the evidence of trying to fix the sensor, but along the line somewhere, someone pulled a fast one.
 
I'd want to verify the gauge is right. If the engine is still running, unless ithe overheating problem JUST started, a cooling problem that bad would likely have killed it in short order.
 
temp gauge

It appeared to work correctly, it was cold when I started it and the needle was all the way cold, then after a couple of minutes it very slowly started climbing. When all the way up before I shut it off. Heater was blowing hot air, all the radiator hoses felt hot except for the main top one, still felt cool, and the radiator itself didn't feel hot except for the cap. There is blue silicone around the thermostat housing, and around the water pump, not sure if either is working properly though.
 
I've got a 71 with I assume the stock temp guage and they are not all that accurate. Mine would peg like yours as well when it got to be about 210+ degrees. Once I put a 180 degree thermostat and electric fan, it would come down a little bit from full, but not much. When I swapped an autometer temp guage and sender in, it reads a perfect 195 degrees all day long.
 
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