running hot/air bubble?

[RuralRoute C-30]

Its been a week since replacing the front & rear seals, then the gauge cluster to get the oil pressure issue figured out.

Now the temperature gauge is running at 3/4 to nearly the red line before the thermostat reacts. Before all this it ran around the middle of the gauge.

Tonight I installed a new 195 degree thermostat, sending unit to the gauge too. Also redid the wire to the sending unit. (when taken off the gauge is sends the gauge to '0'. Even took the gauge cluster apart, (good at that now! and swapped the temperature gauge with the one I was using before all this gauge cluster repairs).

Same thing, gauge doesn't take any time at all to start rising. Reaches 3/4 hot and then the thermostat lets it run to the red and come back down again to around the 3/4 mark.

I read an air bubble in the system might be the cause. Any input on that?

Since the front & rear seal and timing chain was replaced it hasn't been driven more than 20 miles at the most. Now I don't want to take it too far until this is figured out.

Water pump? It is all that is left to replace. No leaks or noise there though and used the old one after the front seal and timing chain was installed. (mistake #?)

Appreciate any input. What is normal for these trucks to run temperature wise? Is the idea of an air bubble a valid one? No sign of water in the oil either. Just suddenly has developed this new "hot" personality!

I swear it just craves for the attention!

Appreciate,
Mark

[RuralRoute C-30]

I let it cool down awhile, it was still warm just not 'hot' when I tried running it in the shop this evening again. Now the darn thing just heats up until the temp gauge hits the red and I shut it down. Doesn't take it any time at all to get hot and it won't back down...almost as if the thermostat is stuck now.

Bad thermostat new out of the box?

Going hot this fast suggest what, water pump not recirculating? Blockage? Bad t-stat? Amazed how it can happen and it didn't even have to leave the shop!

Thinking about draining the system tomorrow after work of fluids, flush the radiator, refill and go from there. With the radiator cap off and running it appears to show signs of circulating. Lower hose is not cold, but not hot either.

But to get that hot at the gauge that fast has it parked for now!

Mark

[kris's66lwb]

youve got your shroud ? check your cap and if your losing coolant if not try parking on a slope up hill facing up hill trun om heater full blast radiator cap off and runn it till the thermostat opens and the water goes down the heater core is usually the highest place in the system i knw this is what i have to do at work on th s class benzs the heater core is the highest point theyre a mother to bleed so try that and see if that helps if not maybe you just got a bunk temp sending unit

[billnorman]

You could have a bad thermostat, or have installed it upside down. You could have a short in the wire or sender problem. You may have a gage cluster problem. Try reading the resistance of the sender with an ohmmeter, and check a friend's sender for comparison if you can't find a factory manual for reading specifications.

[dropd80s]

I have had this happen to me recently in my wifes 99 2dr tahoe. It was an air bubble. To burp the system I had to pull the thermostat housing and thermostat while I filled the rad. As you're filling it make sure you give it a little time for all the air to come up and fill slowly, watch the hole where the thermostat sits, once the coolant level is coming up to the edge of the hole in the intake install the housing ect and top off the rad. When this happened to me the bubble was around the water pump and I ran the motor with the water pump "dry" long enough to burn up the seals. As soon as I got her home from my shop the water pump was weeping horribly. so I had to pull it all back apart to replace it too, something to think about whiole you're in there.

[oldschool18]

I do the same as Kris fill rad up turn on truck turn heater on ful blast and wait for the thermostat to open an add antifreeze.......i do this step twice. I have seen bad cap out of the box from napa and other parts store before...anouther thing,, how close is your cable to your header or mantifold.....if its picking up heat from that then your gauge will read hotter than what is really is.....maybe find someone with one of those infored heat themometors and see what the differance is between the gauge and what you pick up from the engine and see if the two readings are close

[old Rusty C10]

id install the old sender unit and see if that helps it.... if im reading this correct the sender is new but its the only thing you havent switched yet. If that works out then id consider the bubble thing....
Id have replaced the water pump in your shoes when you did the seals
the other thought i had is how are the hoses when the temp guage is pegged? do they seem overly hot?

[RuralRoute C-30]

I've appreciated all the advice. Seems the diagnosis of an air bubble AND a faulty thermostat has made this quite an adventure.

Installed #2 new thermostat tonight with a 1/8" hole drilled in it. Read about this more than once in the search engine here and other places on the net. While this helped it did not 'fix' the air bubble. Yet it did appear to allow the new t-stat to open and close more freely.

Once water flow was guaranteed it has been an evening of run for awhile, add fluids, let sit. Finally took it for a drive and it seemed to start returning near but not quite back to normal from that.

I do happen to have a 45 degree driveway approach so took it out there on the idea there might be an air bubble still lodged in the heater core as mentioned. I think this did the most good. Got it back to the shop, added water and the temp gauge and t-stat seems to have settled down quite a bit from that.

Just waiting on it to cool down once more now and will recheck again, but at least this has been progress!

Even the guy at NAPA today commented when I told him the problem I was having that he just had it happen to an older Buick 350 he was working on that seemed to take forever to get free from a 'bubble'.

Until now, I have never heard of this before being such a pain of a problem.

...and yes, Bob, I knew then and didn't do what I know now was what I should have done and replace that water pump with a new one when that front seal was replaced!

Next time I get into a situation like that with this truck I will listen to what I know is the better thing to do!

Hopefully this is a fix tonight. Letting it cool down one more time to give it a run from the start of the gate so to speak and will let ya all know the final result!

I think I am learning far too much in too short a time since I bought this truck! Definitely a lesson in patience and tolerance! Now if I can catch a break for a few days...a week?

Still happy with the truck...what else matters?

[RuralRoute C-30]

After an evening on this topic and taking it for a few miles out after a complete cool down, the thermostat will open when the gauge needle reaches the 3/4 line then take it down to about halfway to the center line. That's the range it currently is running. Is this an acceptable temp?

Definitely an improvement. Wondering where else to take this cooling issue. Water pump or is it leaning to a head gasket issue?

Truck runs fine, plenty of power, nothing out of the exhaust, just this cooling issue came up now. Since I don't know the truck well enough to know normal everything is suspect. Yet the thermostat is working now and the gauge is not going past the the 3/4 line when the thermostat opens compared to wanting to enter the red zone as it was with no thermostat opening.

A water pump is conceivable. Doesn't appear to be complicated to replace. Just wondering what is left if this is still too hot to run this motor.

Open as always to suggestions or ideas. One way or another this truck is going to work for its keep eventually!

Thanks!
Mark

[RuralRoute C-30]

Just read where the sensor could be wrong for the gauge, yes, Bob, you are right, and I will give that a try!

So I am going to put the old sensor back in tomorrow evening to see if it does or doesn't point the gauge to where the temperature used to be. (used to run around the middle of the gauge and open the t-stat when it went towards the middle of the lines indicating half-way and the 3/4 line.)

And if it doesn't, just one other variable taken out of the equation if this current temp around 220-240 is too high.

(read some opinions on that analysis too).

I may be slow but I am reading!

Mark

[RuralRoute C-30]

Finally had a friend who has a shop test the actual temperature with a laser/infrared thermometer.

It doesn't matter how hot the gauge indicates, the truck is running at 195 degrees. It reached 210 degrees once in the shop then the t-stat opened and back to 195. Checked it more than once at the t-stat, radiator hose, sender unit, and it stayed constant at the 195-210 as it should.

Diagnosis: Cooling system is operating as it should. Probably a bad wire or ground not making a good contact somewhere that is effecting the reading at the gauge cluster. That is why it didn't matter which oem gauge I had, both would read inaccurately with the problem in the wiring from the sender.

His solution/I agree: Install a mechanical temp gauge and do away with the old electric one altogether.

Question: Can I just install a new off-the-shelf mechanical gauge in the oem cluster where the old gauge is? What size is the oem gauge? Any suggestions?

Otherwise I'll just go the route and put one under the dash at this time. It would be nice to take a break from working on this truck and begin using it as it was intended!

Note to self: Ask for laser/infrared thermometer for Christmas!

Glad that is over...I was contemplating worst case scenarios this morning!

Mark

[68Timber]

Did you put the old sender back in?

[RuralRoute C-30]

Couldn't find it but its somewhere in the shop. Even if I tossed it in the trash, the trash can hasn't been emptied.

If I do find it will put it back in just to see. Was in a hurry tonight after work to get over to my friend's shop as he was closing soon.

This truck had mice at some time before I got it, so the electrical issues are not surprising me anymore.

Mark

[Stitch]

I wouldn't cut your dash for a gauge...I had the po do that to mine and it has been a pain in the rear getting it back to factory...I had to replace the black piece in front of the gauges, the gauge lens, and the gauge bezel...what a pain...and then on top of that the stuff that was in the truck was in real good condition besides being cut...I vote for under the dash...or do all the gauges in the dash aftermarket...

[mightyatom]

I just resolved a similar issue with mine. Turned out to be the new temperature senders (PN WT231 - I think) I bought from Kragen (O'Reilly) were not correctly callibrated. I tried 2 different sensors with the same result. Finally got an NOS temperature sender from American Classics and now it does not go above 1/2 scale.

Below is the thread in case you want to take a look.

http://67-72chevytrucks.com/vboard/s...d.php?t=393670

Hope you get it sorted. All the best.

[westofb]

Did you put some type of sealant on the threads of the sender...like teflon tape? If you did, you shouldn't have, the sender goes in without sealant on the threads so it will ground properly to the block, with a sealant on the threads will not work at all or give you errant readings. Just a thought, I did not see anyone mention it in the thread.