150 degree operating temperature too low?

[thegreatjustino]

I've always been told that an engine running too cold is a bad thing.

I have a 351 in my '74 that was in there when I bought it. According to the stock temperature gauge, the operating temperature is around 150 degrees.

Thinking this might be a gauge issue, I used an infrared digital thermometer to take the temperature reading at the intake manifold near the temp sending unit. Sure enough, digital thermometer reads between 150 and 160 degrees.

I have no idea what thermostat is installed or if there's even a thermostat in there.

On top of this temperature issue, the oil pressure is pretty low. Stock sending unit and gauge. At 70mph on the freeway, the gauge reads in the lower quarter to one third. In my experience, it should be about halfway up the gauge at freeway speeds.

I'm curious if the low temperature of the engine is not heating the oil up enough to flow correctly and is negative impacting the oil pressure.

Curious what the experts here think about both of these issues.

 

[B RON CO]

Hi, I would put in a new thermostat. Now the engine is not fully warming up. I like 180* Motorcraft thermostats. I know a lot of guys run hotter thermostats. All in all, the engine will run cleaner at a higher operating temperature.
The oil will run thinner and oil pressure will be lower in a hotter engine. If the pressure is really low at idle, when warmed up, verified with an oil pressure gauge, the engine MAY be showing wear. The only way to tell is to drop the pan and inspect some bearings.
On many engines an easy way to raise your oil pressure is to use a thicker oil. I would try 20W-50 oil, and a bottle of Lucas oil treatment and see if you get more oil pressure.
Good luck

 

[BroncoJimbo]

The stock gauges are little more than "idiot lights that sweep". I use one of these on my older vehicles. Cheap, reliable and you can hide them almost anywhere. Why guess?

 

[Broncobowsher]

Does the gas gauge read low as well? Might be a bad IVR (Instrument Voltage Regulator). It outputs a semi-regulated voltage to the 3 gauges. The gauges move due to heat, there is a tiny heater that warms a bi-metallic spring. This heating causes the gauge to rise. If the regulated output is low, all the gauges read low. If it sticks closed, all the gauges will peg and eventually burn out. There are modern solid state ones that hold a steady reference voltage. These work pretty good, but if you operate in extreme temperature it doesn't have the temperature correcting characteristics of the original style, and most people never notice.

Stockton California, the 180 thermostat is probably the better choice. If you were someplace where you really wanted a good heater, the 192 thermostat will make that heater really perform well and is not too hot.

 

[armynavy17]

Engine temp is definitely low indicating a bad/stuck/missing thermostat. Most people on here run 180 or 195 degree thermostats it seems, I lean towards running a 195. Before you put your new thermostat in, make sure and test in on the stove in a pot of water first. It's not uncommon to have them be bad out of the box. I personally see no reason to go with a "high performance" thermostat as long as you test it first, but some people swear by them.

Your oil pressure issue is unrelated to engine temp, and is likely to get worse when you get the engine operating at the correct temp. If you confirm your oil pressure is low with a manual gauge, I'd recommend installing a high volume (not high pressure) oil pump.

 

[nvrstuk]

Cheap easy test to see if you have a tstat w/o pulling the housing. Cut a pc of cardboard the size of your radiator with 3 extra inches at the top. Slide the cardboard in front of the radiator and fold the 3" over the top of the radiator to hold it in place.

Shut the hood and drive off and see if your temp gauge reads hotter or stays exactly the same. Same temp and you have a 160 tstat.

Gauge reads higher - - like maybe 180 or 195 but doesn't overheat and STAYS there then your engine just runs cold.

Check your heater temp with your bare hand to compare it. If it's really running at 160F your heater will feel warm.. If the cardboard takes your engine temp up but stays at a higher temp you will definitely notice the increased temp thru your heater core (if it's working properly- you do live in sunny Cali

I had a 180 tstat in my Bronco for close to 20 yrs and my Bronco would never reach tstat w/0 cardboard. Had buddies with 351's we couldn't get to run cool and mine was the exact opposite. I got mine up to 210 once when towing our 18' boat up over a long grade on a mid 90's day because I'd forgotten to remove the cardboard- it was May and it was still in!!

 

[Timmy390]

Buy a set of mechanical gauges and confirm what's going on with both oil and water. I run a set in my Bronco, the 69 Mach 1 and my Samurai. I do not trust those old gauges or "idiot" lights. Too much invested to not know the true facts of what's happening.

I run a 195 but I'm EFI and it likes the 200-210 operating temp range.

Remember, the temp rating of the stat is where it STARTS to open. It should take 12-15 degrees hotter for it to open all the way.

Tim

 

[Rustytruck]

open the radiator cap and run the engine if there is no thermostat it will start flowing coolant right away if not watch when the radiator starts flowing. in the old days we would check the coolant temperature with a candy thermometer. don't open a hot cap start the engine with the cap off when cold.

the big problem when running the engine cold is the cylinder wears tapered going down from the hot at top to the cold at the bottom. this wears the bottom of the cylinder bigger once that is done the rings cant expand and contract fast enough and the cylinder wears more at some point the rings cant keep up and the engine starts passing oil flooding oil into the rings then the oil burns and sticking the rings now the rings fail and you get old smoky joe.

 

[thegreatjustino]

I got the build sheet for the engine from the guy I bought the Bronco from (see attached photo). If I'm reading the second line item correctly, it appears they installed a 160 degree thermostat, which would correlate to both the gauge and the intake manifold temp measured with the infrared thermometer.

To answer Bowsher's question, the fuel gauge isn't anywhere close to accurate. The crappy aftermarket sending units never work with a darn.

I will need to get a manual pressure gauge for the oil and see how accurate the stock gauge is.

Thanks for all the replies so far.

 

[MarsChariot]

A useful graph for thinking about operating temperatures that will make you seek 190F thermostats from now on. ***Warning**** Once sen it cannot be unseen.

 

[nvrstuk]

Sounds like you figured out the tstat temp easily- that's great. No need for the cardboard test!

Do you need your heater? Bump up that tstat temp and enjoy some heat if you'd like it or need it! Makes a world of difference.

 

[SHX669]

Both my Broncos run better with 190* t stats than they did with 180s and Like they said ^^^ your heater will work better with the 190 T Stat

 

[thegreatjustino]

Sounds like you figured out the tstat temp easily- that's great. No need for the cardboard test!

Do you need your heater? Bump up that tstat temp and enjoy some heat if you'd like it or need it! Makes a world of difference.

The guy who built this Bronco bypassed the heater. The box is still under the dash, but the heater hoses going into the heater core have been removed and the ports plugged. One of these days I plan to get it operating again, but that project is way on the back burner at the moment.

 

[Rustytruck]

It would be on the front burner if you lived up north. its not a bad job with a new heater core and the foam rebuild kit. use 3m super 90 spray adhesive and for the heat control valve use the plastic one from Napa. once done your defroster will work great as long as your ducting and vents are intact well worth the weekend investment.

 

[thegreatjustino]

It would be on the front burner if you lived up north. its not a bad job with a new heater core and the foam rebuild kit. use 3m super 90 spray adhesive and for the heat control valve use the plastic one from Napa. once done your defroster will work great as long as your ducting and vents are intact well worth the weekend investment.

The defroster duct has been removed from behind the dash, so that needs to be replaced as well. That endeavor will require removing the dash or attempting to get it installed without removing the dash. Neither is an option I'm looking forward to.

I drive this Bronco only five or six times a year so the heater isn't a high priority.

 

[nvrstuk]

I'd drive this beautiful red cruiser of your's 4-5X/week! I like it!