Hot on startup

[LEB Ben]

Alright fellas...let me first state, this is in my 79 Bronco, and no I don't have real gauges yet.

Now to the business part...I set the choke on my Bronco with a 351M, and the normally reliable dumby temp gauge jumps to the hot side instantly. The gauge has never gone past the 'O' in Normal even on the hottest days towing. I can manually bring down the needle if I keep my foot on the gas at around 2k rpm, but as soon as I let off the gas, the needle jumps up to hot again. Now as the engine begins to warm after about 3 minutes, the needle will start coming down on its own. And when the truck is fully warm the needle stays in it's typical spot that I said above.

That said, I'm running 20w50 because it needs it until the rebuild. So with the recent cold snap in single digits is this oil too thick upon start up? It was just fine 5 days ago when it was above freezing. So when it's as cold as it's been, should I just swap to a thinner oil?


Next I was thinking a possible sticky t-stat...but I've never had one stick at start up...so is this an option too?

Lastly, the radiator is on it's last legs with pinholes patched with JB Weld. Is it just time to replace the radiator, or should I just try flushing it? Although it's been my experience that flushing is the final death sentence allowing the crud to dislodge and show all new problems.

Another avenue is, I know that the cold can cause quirks to pop up in these rigs, and is it possible that the dumby temp gauge is gonna be one of those quirks? (I know reaching for straws)

So to recap...the truck runs really hot upon start up, but when it warms up, it's perfectly fine. So in advance, thanks for any tips, pointers, info.

 

[Mil1ion]

Verify you have a temp sending unit for GAUGES and not for a warning light.

They are different.
Because they work on a ground out with power signal.. I would suggest the SU is either wrong or pooched.

The other possible is the ICVR could be corroded and is causing problems.

That's why after 20-25 years the the cluster should be removed and the corrosion removed.

 

[LEB Ben]

Thanks Dennis...it is a SU for the temp gauges. However, I noticed the wire was crimped a few weeks ago and tried to patch it up...so that could be an issue. I wouldn't doubt corrosion would be an issue, because I've only had the rig a few months and haven't really gotten a chance to tear into everything I would like. I just thought it was odd that a few days ago everything was working perfectly perfectly, and last night and today I've had the same issue.

 

[fatherdoug]

Would a problem with the ICVR cause problems for the other gauges as well? I.E. Gas gauge jumping around, etc?

 

[john112deere]

The truck actually pegs the gauge instantly?

Sounds more like your gauge is just wrong...like it's reading backwards.

Even if you start the thing with no water pump belt in the summer, it won't go full hot instantly.

 

[LEB Ben]

The truck actually pegs the gauge instantly?

Sounds more like your gauge is just wrong...like it's reading backwards.

Even if you start the thing with no water pump belt in the summer, it won't go full hot instantly.

That's kinda what I'm leading towards also. The gauge doesn't instantly peg, it moves up the range to the hot side within 2-3 seconds. Maybe I didn't actually fix the wire I had some issues with. But I gave the radiator a check, everything is good. Seemed like there was good oil flow. Since I haven't had oil that thick in conditions this cold, I didn't know if 20w50 would be so 'sludgy' that it would cause such a nasty dry start that it would cause instant temp rise. And it got too dark out before I could pull the t-stat out or really get a good look at the pinched wire. So I'll get on that tomorrow.

 

[Mil1ion]

If a gauge PEGS it means a DIRECT ground with no resistance on the SU
(Faulty SU)/

If a ICVR grounds out on the Pulsing Power signal then it can cause ALL gauging systems.

Oil,Temp,Fuel

Fuel gauge problems are usually the opposite. they usually appear NOT working because the ground at the tank circuit loses ground from rust/corrosion

 

[LEB Ben]

So meaning the wire was pinched and exposed and wedged in a crevice would cause it to have a direct ground resulting in my gauge problem? So then yeah...that's gotta be the problem and I'll fix it tomorrow. Thanks fellas.

 

[73F100Shortbed]

Sounds like the wire is the problem to me. Before reading all posts I was going to suggest sending unit

 

[bucks77ford]

I agree with what others are saying. See what happens with the SU replacement first, then check out the cluster, but I'd also maybe get a "real gauge" to see exactly what the temp is. I'm sure you are going to get a set of guages eventually, but maybe just get a temp gauge and temporarily hook it up to see.

 

[LEB Ben]

Yeah buck...I was plannin on gettin some real gauges but was hopin to put it off until the engine rebuild. You know I'm a HUUUUUGE advocate for real gauges, but just didn't have a use/need them until now. Ain't that how it goes. But I guess O'Reilly's is callin my name and I'm sure I can wrangle something up under $30. I'm gonna get right on that SU tomorrow, only have one class in the morning so I got all day to work on it. Thanks for all the help and replies fellas.

 

[LEB Ben]

Alright fellas...finally got the Temp Sending Unit in, and it reads perfectly, never knew how far off my other one was, and there is no eradic readings either. However, the old SU screwed in flush with the block, the new one doesn't. I put pipe tape on it, and it has flared threads, so I got it as tight as I could but didn't wanna over do it and strip it out. It has about 2-3 threads still showing, but it reads just fine. Should I keep tinkering with it? or leave it as is? And no, it is not cross threaded, and yes it is reading just fine.

I do have to say, it was a little more time consuming than I thought it was gonna be, took me about an hour. It's about 3" behind a bracket and has tons of hoses all around it. So first I realized I couldn't get a socket on it, then my 11/16 BE/OE was too long. Then I got a shorter one and could only get about a 1/4 turn at a time. The most time consuming part and most irritating was trying to get the new SU in, big hands and tight spaces don't go together. So after about 20 mins of dropping the SU and not being able to get it to line up, I finally got it threaded in a little. Then back to 1/4 turn at a time and I got it as snug as possible.

 

[bucks77ford]

If it's not cross-threaded and it's snug, I wouldn't mess with it. Maybe just look from time to time to make sure it's not leaking.

 

[LEB Ben]

If it's not cross-threaded and it's snug, I wouldn't mess with it. Maybe just look from time to time to make sure it's not leaking.

Yeah Buck I figured that's what I'd do. Seems to be holding fine now after about 60 miles worth of driving. I just didn't know if someone here would give me a 'Duh-Huh' answer and tell me I did something wrong. But it seems fine as is.

 

[bucks77ford]

Good thing now is, you can wait a bit to get a nice gauge setup since you now have the factory one fixed because you need a different set of tires.

 

[73F100Shortbed]

It should be fine Ben. I've installed some sending units on various cars and some didn't seem to sit exactly like original but have never run into a problem leaking or anything like that. As long as it is snug you sbould be fine. The pipe tape always helps too.

 

[LEB Ben]

Good thing now is, you can wait a bit to get a nice gauge setup since you now have the factory one fixed because you need a different set of tires.

Thanks for always looking at the positive Buck. I think I got something in the works from an NC 4x4 forum I'm part of. 5 36x12.5x15 TSL Radials with 1000 miles on them for $500, doesn't sound too bad to me.

It should be fine Ben. I've installed some sending units on various cars and some didn't seem to sit exactly like original but have never run into a problem leaking or anything like that. As long as it is snug you sbould be fine. The pipe tape always helps too.

Thanks for the reassurance man, exactly what I was looking for to make me feel better.

 

[Mil1ion]

When using teflon tape one has to realize not to use too much as it will hinder the grounding out the S/U has to do to work properly.

One layer of tape is sufficient.

 

[LEB Ben]

Well I think I used 2-3 layers. You think having 2 threads exposed is worth redoing the job Dennis?

 

[73F100Shortbed]

2 layers should be ok Ben. I wouldn't worry about it too much. If your gauge starts acting up again then maybe consider doing it over, but personally I would leave it alone. Just my opinion