Temp Gage Quit Working

[RonD]

If you have the IR temp reader then test the upper and lower hose, should be about a 20deg difference, after warm up
And test it with RPMs at say 1,500 and at idle

 

[franklin2]

A radiator guy showed me how to check a radiator to see if it's clogged;

1. Drain the coolant

2. Take the lower radiator hose off

3. Get a garden hose

4. Hold the palm of your hand over the lower radiator outlet to seal it off.

5. Fill the radiator with water.

6. Pull your hand off the bottom outlet.

The water should flow out full volume and smooth from the lower outlet. If it's only half volume or gulping, then the radiator is clogged.

 

[ford4wd08]

I'll work on it and report back this weekend.

I bought some flush and the kit for the heater hose to fill/flush.

I'm going to do that first just so I can clean out the block too.

Then I'll probably remove the radiator and clean it with CLR and check for a clog.

If that doesn't fix it, sounds like it might be time for a water pump.

 

[ford4wd08]

I flushed the radiator.... I don't think that was the issue. Radiator seemed to flow out water well, it needed to be flushed for sure.

I'm leaning towards water pump now, I filled it up and let the bronco idle to get the thermostat to open. I could feel the upper radiator hose get warm. I would squeeze it and hold it tight, but I never felt pressure build up and never heard noise of water rushing when i let it go. I also watched it when i had the radiator cap off. I couldn't really see any coolant flow...

Any suggestions or further test?

@RonD @franklin2 @19Walt93

 

[RonD]

Well upper rad hose doesn't have flow when thermostat is closed, right..............
So squeezing it closed when thermostat is open would be the same as thermostat closed, there would be no changes, no pressure build up

Open Thermostat and upper rad hose are just an easier path for coolant to flow than heater hose, so some of the coolant goes that way, some goes thru heater hose, more does when thermostat is closed
Some always flows back to block

 

[ford4wd08]

Well upper rad hose doesn't have flow when thermostat is closed, right..............
So squeezing it closed when thermostat is open would be the same as thermostat closed, there would be no changes, no pressure build up

Open Thermostat and upper rad hose are just an easier path for coolant to flow than heater hose, so some of the coolant goes that way, some goes thru heater hose, more does when thermostat is closed
Some always flows back to block

That's true now that you say that... I just read online that was a way to test for water pump issue.

What is another way to test the flow of the water pump?

 

[19Walt93]

Early 2.8's had the thermostat in the lower water inlet, not in the upper outlet like most everything else. If you ran flush chemicals through it, make sure you pulled the block drains and got it all out or you'll end up with corrosion problems. I've seen a few of the bi-metal gauges fail but the constant voltage regulator failed way more often. If the CVR is the problem, the gas gauge will also read high. I'd also look closely at the radiator cooling fins, if they're dirty or corroded the radiator's ability to cool is reduced dramatically.

 

[ford4wd08]

Early 2.8's had the thermostat in the lower water inlet, not in the upper outlet like most everything else. If you ran flush chemicals through it, make sure you pulled the block drains and got it all out or you'll end up with corrosion problems. I've seen a few of the bi-metal gauges fail but the constant voltage regulator failed way more often. If the CVR is the problem, the gas gauge will also read high. I'd also look closely at the radiator cooling fins, if they're dirty or corroded the radiator's ability to cool is reduced dramatically.

Yes, my 2.8's thermostat is in the lower water inlet. It is a pain to change.

I am still thinking of doing the water pump... It is 36 years old and it sat for 7 years. Just sounds like a good idea to me.

I did find a NOS stock one on ebay for $21, so I just went ahead and ordered it.

 

[RonD]

And you would use a 180degF thermostat on lower hose, even 170degF would be OK
Upper hose used 190-195degF thermostats

A lower hose thermostat should be rated 15deg lower than upper hose/engine desired temp

 

[ford4wd08]

And you would use a 180degF thermostat on lower hose, even 170degF would be OK
Upper hose used 190-195degF thermostats

A lower hose thermostat should be rated 15deg lower than upper hose/engine desired temp

Really? I had no idea about that. I don't remember what the one I had it in was rated, but I believe I put a 192 degree in the lower housing.....

That could contribute to my issue I'm sure.

 

[RonD]

Yes, the radiator provides 15 to 20degF of cooling, and that's also the difference between upper and lower engine coolant temp

And best operating temp is with coolant at 190-195degF at upper engine, from SAE study
So when lower engine coolant is at 180deg upper is at 190-195deg and radiator should start to be used

So yes, check the box or part number of the last thermostat installed, should be max. 180deg
The 2.8l did have hot spots in the heads, just a design flow goof, so 170deg certainly wouldn't hurt in Tenn.

 

[ford4wd08]

Yes, the radiator provides 15 to 20degF of cooling, and that's also the difference between upper and lower engine coolant temp

And best operating temp is with coolant at 190-195degF at upper engine, from SAE study
So when lower engine coolant is at 180deg upper is at 190-195deg and radiator should start to be used

So yes, check the box or part number of the last thermostat installed, should be max. 180deg
The 2.8l did have hot spots in the heads, just a design flow goof, so 170deg certainly wouldn't hurt in Tenn.

I know it was a 192 that I installed, I can remember..... Guess it is time to buy a cooler one.....

I'm trying to find one with a jiggler in it too. I assume that can only help with it being a lower mounted thermostat.

 

[RonD]

Wouldn't hurt but the jiggle valve/hole is to let air out which wouldn't be an issue with lower thermostat like it is with upper
Water/coolant will flow down in rad and engine side to lower thermostat displacing any air because upper hose and rad cap is open to let air out

With upper hose thermostat the water/coolant flows down into lower rad hose to fill engine side but air gets trapped in upper engine because thermostat is closed so air can't get out, jiggle valve/hole lets air out, or pulling off 1 heater hose(or both) from fire wall, lets air out faster, lol

 

[ford4wd08]

Wouldn't hurt but the jiggle valve/hole is to let air out which wouldn't be an issue with lower thermostat like it is with upper
Water/coolant will flow down in rad and engine side to lower thermostat displacing any air because upper hose and rad cap is open to let air out

With upper hose thermostat the water/coolant flows down into lower rad hose to fill engine side but air gets trapped in upper engine because thermostat is closed so air can't get out, jiggle valve/hole lets air out, or pulling off 1 heater hose(or both) from fire wall, lets air out faster, lol

Makes sense. I went ahead and ordered a 160 thermostat for now. I couldn't find anything but 195, 180, & 160. I'll see how the 160 does.

I plan on fixing the AC on this rig soon and hopefully the 160 stat will help with that....

 

[RonD]

Yes, nothing wrong with that at all, racers always run 160deg thermostats

Thermostats set minimum operating temp, so can't help much with overheating, but 160deg should be open all the way after 8-10min so should keep the temp gauge below 1/2 full time
And 170-180deg(upper engine temp) is plenty warm for heater