Coolant Temp Gauge Weirdness

[91Pioneer]

So I've got a pretty weird situation with my coolant temp gauge. When the truck is started from cold, it reads fine, as it warms up it the gauge moves up normally like it should.

 

But, apparently just before it hits normal full operating temp, it "wiggles" or flickers for a minute or two. It fluctuates between just above the low point on the gauge to about the center mark. After that it works 100% solid again. It fluctuates a bit normally during normal operating conditions, but never moving too far. I can see it drop a bit when the engine is running higher (the water pump is flowing more), etc.

 

So it's the weirdest thing to me. I don't get how it would be unreliable just for a minute or two during a specific stage of warmup, and it does it pretty much every time.

 

Since buying it, I have replaced the block heater and the coolant pressure reservoir. I have also done a full flush using the Prestone super flush and drain, disconnected the heater core, back-flushed it, all that good stuff.

 

I'm a bit stumped on this one. I can't seeing it being an electrical problem since it happens at the same point all the time. The only other thing I can think is that their is an air bubble in the system, but shouldn't it work it's way out and cause other problems like overheating? That was over a month ago that I did that flush so it's had quite a number of startups and runs to full temp.

 

Edit: I realized that I still have that upgraded NAPA (Volvo?) cap to install. I had it on there before I got the new tank, but just used the new Dorman cap that came with the tank. I think I will swap to the tighter fitting cap next and see if that helps.

[91Pioneer]

I posted a short video of what it's doing:

 

[HOrnbrod]

It's electrical. Try a new sender, or remove the one you have, clean the threads and screw it back in tightly. Looks like it may not be grounding well until the head expands with heat and "grips" the sender threads better.

[91Pioneer]

OK. I found out the new NAPA cap does not fit the Dorman reservoir, but it does the OEM one. The Dorman tank has a bit bigger lip so the new cap doesn't even fit at all, I'll have to trim it slightly to get it to work.

[cruiser54]

It's an electrical issue. Sender, as Don said, threads grounding, connection......

[91Pioneer]

I've done a bunch of your Renix tips but have not tackled the 6 brown wire grounds yet. Sounds like I need to put that higher on my to-do list  :thumbsup:

[cruiser54]

I've done a bunch of your Renix tips but have not tackled the 6 brown wire grounds yet. Sounds like I need to put that higher on my to-do list  :thumbsup:

Could be...

 

And Post 18 maybe? 

[91Pioneer]

Need to do that one too. Good thing is it's not affecting driveability.

[91Pioneer]

I swapped out my valve cover gasket with the top notch Fel-Pro PermaDry one (it's awesome by the way), and discovered in the process I guess the temp sender at the very back of the block by the VC, the wire came off. And I looked at the connector and it was too big/loose. I crimped it down tight and reinstalled it, cleaned up the threads with brake cleaner, and so far the weirdness has not come back.

 

So all along it may have just been a loose connector on the sender. I'm not sure if I made the connector loose when I bumped it when removing the VC or if it was loose before. Anywho, thought I'd post an update in case someone else has the same problem in the future.

[cruiser54]

I swapped out my valve cover gasket with the top notch Fel-Pro PermaDry one (it's awesome by the way), and discovered in the process I guess the temp sender at the very back of the block by the VC, the wire came off. And I looked at the connector and it was too big/loose. I crimped it down tight and reinstalled it, cleaned up the threads with brake cleaner, and so far the weirdness has not come back.

 

So all along it may have just been a loose connector on the sender. Anywho, thought I'd post an update in case someone else has the same problem in the future.

What's the bottom line in my signature? LOL.

[91Pioneer]

LOL I know, I'm still tackling the list. Slow and steady wins the race. At least I didn't replace anything first, I just happened to be taking things apart in the area :-)

 

I picked up an exhaust manifold today (used OEM) to replace my cracked one so having more things apart will give me another good opportunity to check wiring/connectors/grounds/etc.

[cruiser54]

LOL I know, I'm still tackling the list. Slow and steady wins the race. At least I didn't replace anything first, I just happened to be taking things apart in the area :-)

 

I picked up an exhaust manifold today (used OEM) to replace my cracked one so having more things apart will give me another good opportunity to check wiring/connectors/grounds/etc.

I meant the R*C*B*R*C one!!!!

 

You're all over this, I know. LOL.

[91Pioneer]

I know what you meant, that's why I said I didn't replace any parts first.

[cruiser54]

I know what you meant, that's why I said I didn't replace any parts first.

Gotcha. I misunderstood.