Running too cold?
 

Picked up my 68 Firebird this past Feb. It's a numbers matching car with a 400 HO. Spent the past 3 months cleaning up, replacing some parts and fluids, rebuilding Quadrajet, etc. Been taking her out on some road test cruises. I'm running a 180 thermostat. The rally temp gauge in the dash is reading 140 after driving around for awhile. Also running a Thermocap radiator cap that reads the same thing. Put in a new 180 thermostat today and got the same 140 reading after driving over 40 miles. I did see it go up to 150 during some stop and go traffic in today's 80 degree weather.

I am running distilled water with Water Wetter in the radiator for rust prevention. Initial timing is set at 14 degrees BTDC w/ vacuum advance disconnected. 93 octane, no knocking. Using manifold vacuum for distributor advance.

Is it ok to run at that temp?
Thanks

No. 160 is the minimum recommended, hotter is better for longevity, within reason. Newer vehicles with electric fans sometimes don't turn the fan on until 210+ degrees

I'd like a "third opinion" on how hot the engine is REALLY getting. A QUALITY mechanical gauge plumbed into the intake manifold would be best.

Get a laser thermometer and point it at the spot your gauge is measuring. Need to make sure your gauge is right first.

Basically if your thermostat is actually working it's impossible for it to run 20 degrees below the rating of the thermostat. It could be neg 20 outside and it should still run within 5 degrees of the thermostat rating.

At the cap is a bad place to check temp ... it's on the "cold" side of the radiator. If you have a infrared thermometer ... I'd try to shoot the driver side radiator tank to get a feel for average temp of water leaving the engine.

If it truly is running that cold then it's not good for the motors longevity, no less fuel usage and power, because heat is power!
A internal combustion engine is running on expanding hot air, so always keep this in mind.

Running that cold means the motor is likely taking longer to warn up then it should and test conducted long long ago prove out that 70 percent of all the ware a engine acquirers takes place between the time its cold and up to normal a normal temp.

The oil temp in the motor needs to atleast get up to the boiling point of water so that the normal condensation that is a byproduct of combustion gets sucked out of the motor.

If your just crusing around with light throttle at 2500 rpm even with a water temp reading of 160 it's unlikely that your oil temp will get up to above the needed 212 degrees for a much longer time then it should!

And the size ( cid ) and main jurnal size of the motor makes a difference also.
On my oil temp gauge I found that my 455 got up to 230 degrees of oil temp near 5 minutes faster at 3000 rpm then my 400 did!

We prefer to run our engines on the cool side. Not 140 cool though.

Technically it's impossible for an engine to run 140 if you're running a 180 stat because it won't even be close to opening. A stat forces the engine to run at or near it's rated temp give or take about 5 degrees. The only thing possible in this scenario is the engine running way "above" the rated temp which means you have other issues.

I'd like to see the temperature measured with another gauge and/or shoot the hot side with a temp gun. Something is off.

Something like this: https://www.summitracing.com/parts/sum-g1054?rrec=true

What thermostat did you specifically put in the car? During the cooler months I have the same problem, car refuses to heat up.

I went with one of those high flow thermostats and it’s junk. On the list right now is to get an oem style/quality stat in there.

I'm using a NAPA premium thermostat. The housing is marked MotoRad. Both thermostats are marked 180.

What do your spark plugs look like?

Try turning on the heater .... at 140 it would just produce luke warm air.

Like everyone else ... I would suspect the gauge. The cap gauge should read around 140 or less ... it's on the cold side of the radiator, and the factory gauge, unless it's been rebuilt is probably no where close to correct.

Spark plugs look good.

Blower motor not hooked up yet. Car originally had ac. Has ac delete now.

Car is down for this week. Rag joint needs replacing and have brake fluid leaking from between back of master cyl and booster.

Going to get laser thermometer as suggested and take readings after repair work is done.
Appreciate the replies!

From what I've read, that's typically the temperature sending unit's fault (even
GM replacements). I'm just parroting info I've gleaned from Peter Serio's posts,
he likes Lectric Limited for senders, and he's THE gauge guru. :hail:

My '72 LeMans ran at 160 °F today with an outside temp of 72 °F, on the highway running 70 mph. I used to run a factory 7 blade fan with a Hayden clutch, 160 °F Tstat and it would get over 200 °F idling on a 90+ day. I took the stock fan/clutch out and replaced it with a 7 blade flex fan and it would not get above 165 °F on a 90 °F day. I changed the Tstat to a 180 °F and now it gets up to 175 °F on a 90 °F day. The heat is hot even when it's running at 140 °F on a 50 °F day so it is opening. I am going to try a 190 °F Tstat to try to warm it up.

I have a 5 blade flex fan and no shroud. Also tried another sending unit.

Does a '68 Firebird have a vertical-flow, or a cross-flow radiator?

The big advantage to a cross-flow rad is that the pressure cap is on the cool side, where a vertical-flow rad has the pressure cap on the hot side.

That's nonsense, and not even close to accurate.

Heat is power? LMFAO. Why the hell are racers doing everything they can to keep their engines cool? COLD AIR makes power, because it is more dense. The cooler the engine, the cooler the carb and the intake, which makes more power. Good grief, you couldn't be more wrong.

Oh, and oil doesn't have to reach the boiling point to release any condensation. Ever spill water on a sidewalk on a hot day? What happens to that water? Do you think the sidewalk is 212+ and the water sizzles off? No. And that's at atmospheric temp, not at a vacuum like any crankcase should be (which lowers the vaporization point).

The temperature that modern engines run at has nothing to do with heat making power. It has to do with emissions, and CAFE standards. 140 is a little on the cool side, but it isn't going to hurt anything.

I'm sure Peter is correct .... and yes the obvious far easier to replace the sending unit than rebuild a gauge.

Navy horn your comments prove that have no clue as what in accutality takes place when a air and fuel charge injested into a cylinder gets ignited and the burn / flame front starts to expand.

The level of heat that is produced when the flame front starts is the sourse of power!

When steam locomotive engines where able to get away from the old slide valves they used and go to poppet valves engineers then found they where able to do / apply what they called super heating.
This is where they send the 400 degree steam back thru the boiler again and bring its temperature up to near 700 degrees, this in turn allowed a given volume of steam to do more and more work equals more power, and it's the same dam thing as it relates to the burn rate in a combustion engine cylinder!

Yes you need to injest the coldest air and fuel possible into a combustion engine cylinder, but at that point of ignition things change over to a whole other set of factors!

And if we are talking about maxing out power then emissions and CAFE standards needs to stay out of the picture.

170* T-Stat
 

This is any interesting topic. I started my Pontiac Journey acting as ‘scrub nurse’ for my older brother and his best friend on the weekends while they worked on their Pontiacs. This was circa 1983. Back then, HO Racing and Nunzi were the only players at the table for aftermarket Pontiac Performance. And I remember both offering ‘cooling kits’ as an introductory upgrade that included 4-row factory style radiators and 160* T-Stats. My brother and his buddy both had 160* T-Stats in their cars - which ran notoriously ‘warm.’ Maybe the 160 stat was a crutch for an inefficient water pump? I will say, my brother’s car had quite a bit of compression for the street by today’s standards: 670 heads on a 428. There were no aluminum heads available back then. I believe his friend’s car was a ‘bit’ more pump-friendly with a set of heads from a 350 on his 400.

Fast forward - when I first got my Red 73, she got SO hot the first night I took her to a local cruise night that she literally vapor-locked and died right there in 4-lane traffic. I limped onto a side street, threw the hood, and sat for about a half and hour and then limped her the rest of the way to the event. By the time the sun went down (along with ambient temps) she ran fine - albeit pretty warm - all the way home. Of course, I did the kitchen sink routine: 4-row factory style radiator, Flow Kooler water pump and 160* stat. That car will run virtually dead on 160* (verified with a heat gun) form the coolest days in fall and early spring all the way up to the hottest day of summer that I’m willing to sit in a car with black vinyl interior and no AC. Point is, the current low-tech cooling system is incredibly reliable.

But I have often wondered if the car would run more efficiently at another 10* of operating temp? I just have never wanted to leap back into a 180* stat only to find that she pings and chugs after I turn the key off on a hot day. I always wished there was an option for a 170* stat rather than taking a 20* step to see what happens.

In reading this thread, I did a bit of a dive reading posts on other forums and I found a supplier who sells Custom in-house built 170* stats for virtually all makes including GM / Pontiac. If you back track from this link, there is a ton of info on this site about how coolant temp affects performance:

https://www.lethalperformance.com/re...hermostat.html

Thermostats start to open at their stated temp and open all the way 20 degrees later.

Just for grins, I was having issues with t-stats. I had a 180 deg. but the car would never get to that number. I thought it was the factory gauge. I experimented with different coolant levels in the radiator and of course it went above the 180 so I knew it wasn't the gauge.

No real reason to be afraid of a 160 stat. An engine will only run at that temp if the cooling system and everything else about the engine is up to snuff and capable of holding that temp.
In most cases, with stock cooling systems and warm climates, the engine will still run well above that thermostat temp rating. It will just settle in with what your system is capable of.

I have one car here with a 160 stat, with it's original 50 year old radiator, stock cooling system, clutch fan, etc... It generally runs around the 175 mark most of the time, and on the hottest days here in AZ 185 is the hottest I've seen it.
I've since put a Cold Case radiator in it, left everything else the same, and it now does run closer to the stat rating and has a more consistent temp on the hotter days. Hasn't seen 185 since.

Most of our other cars are also 160 stats and efforts made to keep them at or around that temp for various reasons. The biggest being that we push the compression envelope with our engines, and have to run this crappy 91 octane pump gas. Tunes have to be spot on but also just as important to maintain and have good control of engine temps. Especially here in AZ where our summer temps are over 100 degrees. We don't care about emissions, I'm not looking to burn off all the hydrocarbons, I'm looking to control combustion chamber temps and detonation, with sharp tuning, tight quench, proper camshaft, and controlling the engine temps. There is no real downside to it that I've found after doing this more than 30 years.

Actually, not to be nit picky, but interesting none the less and fitting for this discussion, from my testing, I've found that stats actually start to crack open roughly about 5 degrees before their rated temp. Pretty easy to experiment on the stove top with a temp probe.

Then when put in service, if you have an excellent cooling system, you can actually see and maintain that crack open temp.

For instance my chevelle has an excellent cooling system, Griffiin rad etc... and the 160 stat in that car actually cracks open at 155, and is fully open around 165. However, as soon as that stat cracks open, on cooler days of 80 or less, it will maintain 155 degrees and is rock steady. Higher rpm on the highway can make the temp rise to 165 but as soon as I slow down it will pull the engine back to 155. Never any colder than that. So most of the time cruising around, this thermostat never even really opens completely, but it does make the engine run at a minimum of 155, and with a good cooling system, the thermostat just barely cracking open is enough to keep the engine at that temp, and will open more if the temp rises. It's doing what it's supposed to do. It's pretty interesting how this stuff acts with a good cooling system.

Yep, a properly sized and well maintained cooling system should be as spot on and invisible in operation as a central air system in a home. Typical modern auto cooling system will get to the proper temp and stay within a couple of degrees of that in pretty much any outside conditions or load.

I second the suggestion of a mechanical gauge in the intake manifold. I'm not buying that the car is running 140 with a new 180 thermostat.

I must have done that demonstration 100s of times when I taught auto mechanics at a high school.. (And it was in the book.) But what do I know?

Good grief dude, are you seriously referencing STEAM ENGINES to try to justify your nonsense?

The heat being created by combustion goes out your exhaust. Power isn't measured in exhaust gas temp, or exhaust manifold temperature, nor is it related to the cooling system's inlet temperature. These things aren't related in any manner what-so-ever.

If what you said was correct, bigger motors would need smaller cooling systems to run as hot as possible TO MAKE BIG POWER. That's exactly opposite of how builds go. Sorry you don't understand the relation between heat, complete combustion, and emissions. I don't have time to teach it.

Steam engines...LMFAO. I've heard it all now.

It's important to remember that what you get on your gauge is only reading the temperature at one point in the entire cooling system. It should be on your water crossover which is essentially your water inlet temperature. That tells you how hot the water is when it goes back into the motor. If your cooling system is being overwhelmed, it will be really hot at this point.

So you are going to have a pretty big split between your inlet and outlet temp, which is why all these comments about needing to boil water out of your oil are nonsense. Your water temp reading isn't your oil temp, or your exhaust manifold temp, and darn sure isn't some kind of "power" equivalent. A well cooled engine runs better, lasts longer, and makes more power. I run a 160 degree thermostat, and it never gets above 175 unless I'm sitting in traffic in the summer (in Texas).

Before I got my Cold Case radiator, I got stuck in the staging lanes and did a pass with the motor around 205, and was .2 slower than the previous run. Go to a drag strip and ask people if they run their engines as hot as possible or as cool as possible.

Yep, even my sons fuel injected mustang doesn't like heat. We were at the track a few weeks ago and I tried hot lapping it, the car slowed down. It ran it's best times with a full cool off. I keep a 180 stat in that one with a cold case radiator. Preferably I don't like to see the temps above 190 in it because it will ping and complain on our 91 pump gas when the temps get that high, and it's just a bone stock 9:1 engine assembled by Ford. I don't dare run cheaper gas in this one during the summer months, especially with the AC on. Matter of fact when I was hot lapping it, it had some slight ping during the longer pull in 3rd gear. The slow drive back to the pits cooled the car down, a testament to the efficiency of that Cold Case radiator. Then a 20 minute cool down in the pits with the hood up was the ticket for best times. If I had ice I would have been icing down the intake.

While thermostats technically open and close they actually modulate.

OP, did you drill a hole in the thermostat to bleed air?

No. Both thermostats I tried were left stock.

Mine stays at 150 with an aluminium radiator and a stock (no clutch) five blade fan.. car seems happy enough at this temp. Outside temp was around 65-70 degrees..

First thing I'd try is a new gauge.

True.

Clearly NOT. The water crossover is the last point before the thermostat, where the coolant LEAVES the engine for the radiator. The water INLET temperature would be measured at the lower radiator hose area in the water pump.

Because the coolant has already picked-up heat from the engine, and is about to exit the engine to be cooled in the radiator.

The mistake in logic you're making is largely the result of having no practical way to keep the inlet air/fuel as cool as possible while running the cylinder block nice 'n' hot.

Cold intake air/fuel = high-density, good power, reduced detonation
Hot "short-block" = lower friction, less wear.

Folks over-cool the block trying to keep the intake manifold and cylinder head intake ports (and therefore the intake air/fuel stream) cool. As far as the intake air/fuel mix, cooler is better until you have fuel vaporization problems. It needs to be "just" warm enough to deliver a proper mix of fuel with the air to each cylinder; if it's too cold the fuel falls out of suspension in the air stream, doesn't vaporize very well, and too much goes out the exhaust unburned. Welcome to needing a choke and intake manifold heating methods in cold weather--you have to put so much fuel in the air because lots of it is not vaporized and is wasted. This is hardly a problem once the engine warms up.

Good. Drilling holes in thermostats is nuts unless you've disabled the OEM coolant-bypass system.

There's a reason thermostats don't come from the factory with bigass holes in them. True enough, some do have tiny stamped vents, or a "hole" that gets plugged with a "jiggle valve" when the water pump flow increases.

Any air in the system is moved to the radiator as soon as the thermostat opens the first time after cooling system service. At that point, it's seen as a "low coolant level", and the radiator is topped-off. In a properly-functioning cooling system, there is no other source of air that needs to be blown out of the engine.

You are correct, I had the flow backward in my head for some reason. Still, the temperature of the head and combustion chamber being cool is an important aspect that you are overlooking. It isn't just the temp of the air/fuel mix as it goes into the chamber..the temperature of the combustion chamber is important as well.

EngineMasters has done extensive testing on this, and they showed that the temperature of the fuel and air, and the temp of the head itself are what make the difference. The air/fuel mixture is going to fast between the carb and head to have significant heat transfer.

By having a cooler engine, you have cooler fuel, and avoid all the problems that you end up with by having an over-heated cylinder head. It's the whole reason aluminum heads exist (other than weight).

While the car is 52 y.o. this month it's still "new" to me. Before I change anything else I going to order a "heat gun " this Friday. I'll post my findings here after i get some readings.

I've always believe you want a cold(condensed) fuel/air charge to the "hot" combustion chamber. The heat causes rapid expansion of the condensed charge, increasing compression and power.

That is not correct. The spark plug provides the ignition source. Hot combustion chambers can cause pre-ignition and other problems. Hot chambers make less power. The rapid expansion of the burning air/fuel mixture pushing against the enclosed space is what makes the power. Every interaction the particles have prior to the ignition of the mixture favor COLD to make power. Heat is managed and dissipated, it's never desirable. If it was, you can put chemicals that burn WAY hotter than gasoline in your tank. They will just destroy your motor.

Keep in mind the purpose of the thermostat is the set the minimum operating temperature. The thermostat has absolute control over that by preventing circulation until it's preset temperature is reached. Once open, it's up to the efficiency of the remaining components - radiator, water pump, fan - to prevent the temperature from rising above that level. I always chuckle when I read that someone is switching to a cooler thermostat because the engine is running hot when the two issues are not related.

The only way for an engine with a properly functioning 160 degree t-stat to continuously run at 140 degrees, would be for there to be a route for the coolant to be bypassing the thermostat and traveling to the radiator. Are you sure the thermostat is fitting tightly in the intake manifold recessed groove and there's not excess corrosion in this area that could allow a bypass? Are you using the correct "water neck" that fits properly and keeps the thermostat clamped tightly against the intake manifold? Are your heater hoses connected to the standard locations at the rear of the right head and lower water pump housing?

Timing, vacuum advance and thermostat are correct. I wouldn't run distilled water, I'd run filtered tap water, and 50 percent green anti freeze. Reason: altered waters are all ineral starved, and will begin to eat any mineral they encounter, such as gasket materials, cast iron, aluminum.

To confirm, I suggest obtaining, or borrowing a hand held laser type temperature reader, and take a look at block, head and radiator temps. It sounds like either the temp gauge, or sender, or both, are out of whack.

The recessed groove in the manifold is in good shape and clear of all debris. I replaced the thermostat housing at the same time I put in the replacement thermostat using correct OEM style bolts to hold the housing down. Checked bolt protrusion thru the housing against the depth of the threaded holes in the manifold. Bolts were torqued to 25 ft/lbs then re-torqued after running the engine. Heater hoses connected to pressed in head fitting and water pump housing.

When I brought the car home there was no thermostat and the sending unit was not hooked up. Looked like it had been disconnected for some time.

The radiator appears to be original. Not a closed system. Water level is staying at the cold fill marks when cold. No water puking out that I can see.

When testing to see if the rally temp gauge works it went all the way up to 250. Don't know about the accuracy yet, especially with original wires, connections and gauge..

I believe it is just coincidence that the radiator cap thermometer and rally temp gauge are both reading the same. Ordered an infrared thermometer today to find out what's really going on.

Using a candy thermometer wrap the probe end to the upper radiator hose with aluminum foil and duct tape (foil because you don't want that tape glue melting on your hose). On cold start and watch the gauge to see if the needle jumps when the thermostat opens and see just how hot it's really getting, sounds like the thermo stuck open or opens too fast. If you remove it, put it in a pan of water on the stove with the candy thermo, heat then watch when it actually opens. It's odd that the thermo cap would read same as the gauge as the thermo cap gets the water cooled by the radiator and the gauge gets the water heated by the engine (assuming your sending unit is on the intake coolant crossover). At least one or both of your temperature sensing devices is defective, and possibly the thermostat as well.

Update:
Finally got a chance to go out for a cruise today. Avg. air temp 65 degrees. Went almost 50 miles, most on the bypass. Got home, let her idle for 3 minutes and took readings with the infrared thermometer at several locations. Avg reading was 180 degrees when the rally gauge only read around 140. Next plan is to run new wiring to the gauge.

If this does ultimately trace back to the sending unit, I highly recommend the Lectric Limited unit for accurate resistance and calibration:

https://www.lectriclimited.com/tempe...ng-unit-115857

I have the Lectric Limited sending unit in my 72 Formula with 455. Before the switch to this sending unit, the stock sending unit had the gauge reading 210. After the switch to the Lectric Limited unit the gauge reads 140-160 depending on the outside temps and how long I'm idling. Car is equipped with Griffin radiator and Milodon aluminum water pump.

Your system is working perfectly. Just send it.

If your wiring has enough resistance to alter your gauge reading then there is a pretty serious problem. I would be more inclined to make sure you have the correct sending unit for the car. The sender is a thermistor that simply changes it's resistance with temperature. The resistance range of the sender needs to be a match to the gauge that it is driving. If the sender is correct and working properly, I would look at the gauge itself. Not positive, but I assume there is a shunt resistor on the back of the gauge terminal posts just like the fuel gauge has. Most of us have been around long enough to know how the fuel gauge will read way off if the shunt resistor goes bad. Back in the day, all the auto parts stores carried replacement shunt resistors in the card mounted HELP! section.

If you don't mind spending some money, you could send the gauge cluster and sender to Pete Serio and he will calibrate everything and rebuild the gauges as needed. Pete likes to change the way the rally temp gauge works so that there is more degrees of freedom between normal and overheat, since the gauge as originally designed only provides a relatively small area between say 200-250.

However, that requires you to remove the dash to get the rally gauges out.

I wouldn't tend to think that the wiring is the issue since you are getting a solid reliable reading. That's not where I would spend my effort at this point, FWIW.