My coolant gauge might be possessed

[jam sandwich]

So, Im preparing this truck for a 400 mi trip and I want to be sure I don't end up broken down on the side of the road.

I've noticed my coolant gauge NEVER gets above the N mark while driving (I drive 40-50 miles roundtrip to work)
However, this morning, I looked down and noticed the gauge was at the halfway point (around the O and R) I watched closely, and then all of a sudden the gauge just drops below the N again out of nowhere
I was going about 70-75mph @ 2600 rpm or so (4.10 gears) I maintained the same speed during all of this.
If I idle the truck the coolant reading never goes above the N mark either.

I know these old ass gauges arent very accurate, but should I be concerned with such fluctuations? I recently had a coolant flush and added SCA back in. My overflow tank looks relatively normal, its a little offcolor but not as bad as it was when I had oil leaking in the coolant (I replaced cooler o rings)
I've never seen the temp gauge go past the halfway mark.

I just want to be sure this truck is roadworthy before I make such a long trip in it.
Would replacing the temp sending unit be worth it? The rest of my gauges work relatively well, and I've replaced both battery ground cables and a couple more ground cables in the engine bay.. Are there any other grounds I should inspect or replace?

 

[Agnem]

It would be real helpfull if you had a signiture that listed your truck, but since you don't, I'm going to say you have an 83-86 with the cluster that uses the IVR. The IVR is usually the culprit, and you will notice your oil presure and fuel level vary at the same time your temperature gauge is fluxuating, but those gages won't move as much so you won't notice it. Replace the IVR.

 

[jam sandwich]

I'm sorry I have an 89 7.3 idi N/A 5 speed. (I'm making a sig now )

 

[jam sandwich]

Bump. Sig test

 

[icanfixall]

Might be a thermostat going bad. Do you knoe what thermostat is in the engine... There are plenty that fit but wont cool these motors because they can't pass enough coolant.... Only the Ford or International thermostat will work correctly. It starts to open at 192 degrees and is fully open at 212 degrees...

 

[jam sandwich]

I'm not sure whats in there... I assume it might be stock.
I've never had the engine overheat YET. But again I've never driven the truck more than 90 minutes continuously.
My heater core is NOT hooked up because it was leaking, so i bypassed it.
I might be overreacting, but I just want to be absolutely certain these fluctuations are OK and not a sign of imminent failure.

 

[jam sandwich]

I just wanted to follow up to this issue.
I went to the auto store and bought a replacement coolant gauge sensor (8$) and now my temperature readings are ALOT more accurate now. The gauge stays around the O in Normal with slight fluctuations.

 

[fuzzydog]

My experience with my 91 7.3 idi and the coolant gauge is this.

When I first bought my truck, the needle would be just barely off the bottom on the left side (cold). I could run around all day, idle all day and that sucker would barely move. I started thinking I better look into that and get a new sensor or gauge or both. Until one day I was taking the kids snowboarding and was pulling a trailer with two snowmobiles on it. Pretty steep grade up to the ski hill and suddenly the truck starts making this roaring sound and I'm thinking "uh, oh, something gave out" I look down and see the temp gauge at the halfway mark and dropping rapidly. ! the roaring noise was the clutch fan kicking in. Since then I have repeated that many times - I have hauled an older 10.5ft camper (loaded for a week) while pulling a 16' flatdeck with a jeep cherokee on it. The temp gauge would get up to halfway on the hills, the turbo fan propeller on the front of the engine kicks in and the temp drops right down. Now I just don't worry about it. I have a pretty good feel for when the temp gauge 'should' start to rise and if it doesn't when I expect it too, that is when I will change things.

 

[nyteshades]

get a mechanical water temp gauge and take the guess work out of it.

 

[itsacrazyasian]

get a mechanical water temp gauge and take the guess work out of it.

i 2nd that! After i did the swap, the stock coolant temp gauge never went past O in normal no matter how hard i beat on it. With the mechanical gauge i can watch it get up to 210, cool off, theromstat close and open again all while the stock gauge stays at O. I think it should say DUH behind the needle.

 

[crazy4wdracer]

get a mechanical water temp gauge and take the guess work out of it.

This will be my next gauge for sure. They aren't expensive at all either. Around $10-15...

 

[5.0bronco]

i have a mechanical temp guage in mine and it runs at about 160 idleing and wont hit over 190 pulling a load

 

[88beast]

the stock gauges are idiot lights tis that simple
on off or way on and way on aint an option for the temp gauge so... any info you get from it is useless

 

[Kevin 007]

Is there a fix for the factory gauge?

I just installed an aftermarket one just to find out that it didn't work and im not going to drain a bunch of coolant to take the sendor out so I will just leave it for now.

 

[Diesel JD]

Is there a fix for the factory gauge?

I just installed an aftermarket one just to find out that it didn't work and im not going to drain a bunch of coolant to take the sendor out so I will just leave it for now.

Good question, but I have no idea if a good fix can be had or not. Maybe a real electrical sender hooked up to it? I've heard this suggestion for fixing the factory oil pressure gauge as well or at least that was my understanding.