Engine running cool

[dhendriksen]

I’ve got my 1971 back from the restoration shop, and giving it a couple hundred mile shakedown before it goes back for a punchlist.

It’s the stock 302…we didn’t do any engine work other than replacing all the gaskets, having the heads checked and valve seats replaced, then all new accessories (water pump, thermostat, alternator, etc…). It has the factory 2100 carb.

As part of the restoration, it has a brand new painless wiring harness. It also has a brand new temp sending unit. It’s the factory gauges - we just cleaned them up.

The temp never gets above around 150°. What’s the best way to validate the real engine temp, and should I be concerned it’s running so cool?

 

[Lawndart]

Get an infra red thermometer and point and shoot it at the intake near your sensor.
You don't want it running cool.

 

[dhendriksen]

Get an infra red thermometer and point and shoot it at the intake near your sensor.
You don't want it running cool.

What are the possibly bad things that can happen from it running cool, and how urgent is it that I get this addressed?

 

[904Bronco]

There is an early and late Temp sending unit, be sure to check you got the right one.

What thermostat did they install? 180* is standard.

Lawndart's suggestion is good one to start with.
Running at the correct temperature is important to prevent carbon build-up and get good fuel economy, if there is such a thing with a Bronco?

 

[ntsqd]

Where did they install the temp sender? I've learned recently that this can make a huge difference in the temp reported. My Wagon has had it's temp sender installed in the block drain (SBC) down low in the coolant jacket. When the radiator cap is too hot to touch, the gauge says ~150°F

 

[Brush Hog]

You sure it’s reading 150? My stock gauge starts at 120 then the next number is 170. I’d have to get in close and look hard to tell it was 150. The lines are very close. But it is a “stock” replacement gauge from Tom’s.

 

[dhendriksen]

To answer those questions/comments, the temp sending unit is mounted right behind the distributor in the top of the intake manifold.

I did some tests…the thermostat is opening at 195° like it should and the engine appears to be running at a good temp.

As far as saying it reads 150…that’s me taking a swag at the exact number based on its location between 120 and 170 (above 170 and the numbers are more frequent and closer together).

I think the gauges need to be calibrated, so getting the cluster to an expert who can send known values and make sure everything is calibrated appropriately. If it’s still reading wrong after that, I can diagnose further but with everything else being new, and both the fuel and temp gauges reading low, I think it’s a cluster issue.

Thanks for all the input.

 

[DirtDonk]

Where does the oil pressure gauge read? And the fuel?
Before going to the trouble of calibrating the gauges, you might measure the output voltage of your instrument voltage regulator.
Is it original? Is it an electronic replacement?
Most of them can be adjusted. If your temperature is reading cool, and your rebuilt engine has a possibly low oil pressure reading, and the fuel is reading a little low, you might increase the output a little bit.
But measure first.

 

[m_m70]

Before going to the trouble of calibrating the gauges, you might measure the output voltage of your instrument voltage regulator.

Best advice right here^^^^

 

[dhendriksen]

Where does the oil pressure gauge read? And the fuel?
Before going to the trouble of calibrating the gauges, you might measure the output voltage of your instrument voltage regulator.
Is it original? Is it an electronic replacement?
Most of them can be adjusted. If your temperature is reading cool, and your rebuilt engine has a possibly low oil pressure reading, and the fuel is reading a little low, you might increase the output a little bit.
But measure first.

Thanks for the advice. You’ll have to forgive me, but where would I do that? I do have a multimeter.

It’s a brand new painless wiring harness. It’s a brand new alternator. It’s the original instrument cluster.

 

[904Bronco]

https://classicbroncos.com/forums/threads/bench-testing-instrument-voltage-regulator.281521/

It is on the back of the instrument cluster... Looks like this:

https://www.wildhorses4x4.com/early...tdKrls-1mUSXgmatV9MuykU2AFKJPrwJUuSGtfCkVyypw

 

[dhendriksen]

https://classicbroncos.com/forums/threads/bench-testing-instrument-voltage-regulator.281521/

It is on the back of the instrument cluster... Looks like this:

https://www.wildhorses4x4.com/early...tdKrls-1mUSXgmatV9MuykU2AFKJPrwJUuSGtfCkVyypw

Thanks. I found a schematic that shows where it is. So I’m just looking for the gauge on the multimeter to bounce all around between 3 and 7 Volts? How will I know if it’s bad if the value is jumping all over the place?

 

[DirtDonk]

Since it's original, yes it will bounce/oscillate. Unfortunately for those with digital volt-meters. Which are pretty much all of them these days!
I think I might have one analog meter left that has not given up the ghost. If you can find one, try that. If you can't, I think the digital type must have a very fast response time, or it will just give you gobbledygook readings.
Hopefully someone has a better answer, short of using an oscilloscope!

Good luck,.

Paul

 

[Jakedog]

I love the way the stock cluster looks, but I don't trust them for accuracy.
I run a manual temp gauge, and a manual oil psi gauge.
My current gauge set up is not what I had in mind, but a PO cut the dash by the stock cluster. So I just used a flat plate for now.
I will change the set up eventually.

 

[matts460]

Last I remember the Voltage regulator should be reducing voltage to 5volts for the instruments. I wouldn't have figured it would be bouncing around on the reading. To answer another question, usually when an engine runs cool it is most likely a stuck open thermostat. Although that doesn't seem to be the problem anyway. Oh also a 190/195 thermostat was stock through most of the 70's. Mine is 190, but once open runs 180 always with no shroud. (302)

 

[DirtDonk]

Last I remember the Voltage regulator should be reducing voltage to 5volts for the instruments. I wouldn't have figured it would be bouncing around on the reading.

The factory original IVR was an electro-mechanical device, similar to an old-school points type voltage regulator.
It was also referred to as a “constant voltage supply“ which was kind of a funny term for something that oscillated the way it did.
It had high and low readings that averaged out to be 5v or 6V. But it was not constant because it was opening and closing the contacts. Because the gauges themselves were dampened, you didn’t see the oscillations on the needle. Just an average based on the voltage.
It was also temperature compensating, I believe it could be termed, which corrected for the normal variations in system voltage you see during normal operations. Keep engage readings consistent.
In other words, your temperature gauge for example would read 180° whether the input voltage was 12.6 with the engine off, or 14.8 with the alternator charging.
Pretty slick actually…

I’m sure I’m not describing it correctly. Others with more electrical knowledge have described it clearly here.

 

[dhendriksen]

There’s a local vintage gauge restoration expert - I’m just going to pull the cluster and give it to him. I will let him sort it all out and make sure everything is good as gravy with the IC.

 

[m_m70]

There’s a local vintage gauge restoration expert - I’m just going to pull the cluster and give it to him. I will let him sort it all out and make sure everything is good as gravy with the IC.

Cool. When you get his diagnosis please post up. It will be interesting what he finds.

 

[dhendriksen]

Cool. When you get his diagnosis please post up. It will be interesting what he finds.

It’s going to be 3-4 weeks before that happens, but I will report back.