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I started my Broco today and noticed that the temp guage went to half way right away. I drove it and less than a mile it jump past H. Then a couple of min it fell back down to normal and stayed there. I did not think much about it. I drove about 20 miles and did what I was there to do. On my way back it did the same thing so I did not think nothing about it. I got about half way back and I stop at a red light and looked down and noticed it had jumped past the H. I drove it a little farther and it did not come back down. I pulled into a Home Depot and lifted the hood. I was not boiling over, steaming or even making a gurgling sound. I thought if it was running that hot it would be doing one of those. Could be the sending unit? Or, did it realy run that hot? The reaon I thought it was the sending unit is because of how it did this morning and when I was coming back. I left if there just to be on the safe side.:banghead
 

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is there enough coolant in it they will do stuff like that when rather low, if it stays on hot all the time running or not (as long as the key is on) it is probably the sender
 

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Discussion Starter #3
it has enough coolant. I forgot to mention that it did it the same thing on the way back from work. So when I got home I checked the level. It was a little low and I filled it up.

When I looked under the hood after pulling into the Home Depot parking lot I tuned the radiator lid and fluid came out so of course I tightend it back up.

The surge tank was on the full mark also.
 

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if you go out and turn the key on after it has sat awhile does the gage read all the way Hot or all the way Cold
 

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mine is also having a similar problem, it gets up too normal very fast, than if im reving it on the higher side for some time it starts going up, so i let up and it goes back down again. Its going up and down a lot and doesnt seem so great, my levels were fine, no boil over. I was on the highway going 65 @ 2200 rpm and it started heating up so i had to get in the slow lane going 55. Kinda sucks, dont know what the problem is. thermastat or need a radiator flush or something?
 

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Do a resistance check on your temp sending unit. Check it with the engine cold and note the reading and then warm up the engine and check it again. I don't remember if the resistance is supposed to up or down after warming it up but check the Hayne's manual it tells you in there. If that checks out ok then it's probably a sticking T-stat, if it's bad then replace it.
 

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Mine does exactly the same thing. If you pull the sending wire off the sender, and ground it, the gauge should peg all the way hot when the key is on (don't do that for too long). It's possible that your sender is bad, but mine does it with a new sender also. I think it's in the gauge itself. After pegging it by directly grounding it, it works properly for about a week, then starts up again.

Make sure you didn't put teflon tape on the sender when you installed it. It's a heat sensitive variable resistor, which is supposed to be grounded through the intake manifold (or wherever it's screwed in on your truck). The teflon tape messes that up, insulates it from the ground.
 

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colinlesser said:
sounds like a blocked passage, maybe a blocked water jacket

if a passage was blocked then it would probably over-heat and stay overheated. as there wouldn't be any coolant circulating.

edit: if you test the gauge, do NOT hook it up to a 12volt source, you will blow up the gauge, i believe they are only designed to run on 4 volts or some-where around there.
 
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