Technical Radiator cap and getting hot

Will an engine run hotter without the radiator cap on or with a faulty cap? Asking for a friend! Ha!

 

The radiator cap allows the engine to run hotter without boiling .

 

A couple variables. Is it a pressurized system? With a recovery tank? If so, If the faulty cap is not sealing and letting coolant out upon expansion, there's no difference from no cap. If the faulty cap holds a little pressure, that would be better then no cap. I can only assume the faulty cap is not allowing coolant recovery.

 

Bbdakota I’m just running hotter than I like so researching everything possible avenue. New rebuilt engine with maybe 2 hours on it.

 

Got a known good gauge with real numbers on it?
How hot is hotter then you like?
I get concerned when a pressurized cooling system gets near 230 degrees, or starts boiling over or blowing coolant out. Are you near there (within 5 degrees) yet? Gene

 

- what is that temp Number? - post pic of what you are working on

 

Yes.

 

Also you could have air in your coolant system. It may need burped.
How hot do you consider hot?????

 

A pressure radiator cap allows the boiling point of the coolant to raise in relation to the number of pounds the cap is rated at.
It does not in any way cause the engine to run hotter, it allows a cooling system to operate hotter without boiling over. Yes the engine might run hotter before the radiator pukes than it would without a pressure cap but that won't help the engine run cooler especially if your version of "too hot" is under 212 F.


If the engine is actually running hot you have to figure out if it is coolant flow or capacity or air flow.
The radiator being too small to cool the engine of choice has always been an issue with hot rods as that is what fits in the space even when it isn't up to the task.
Then add in a radiator or cooling system that doesn't flow right due either to a clogged radiator or corroded and somewhat clogged cooling system inside the engine. Or a pump or pump system that doesn't move the coolant right.

Air flow, probably the biggest issue especially if the engine runs at the temp you like but gets "hot" when you slow down. That is normally caused by not enough air flowing through the radiator to carry the heat off. Normally not enough fan or no shroud or fan mounted at a point where it really isn't effective in getting air though the radiator.

All of that simply means that if everything else is right your engine should be running at the temp you want no matter what the pressure rating of the cap is. If the engine is running 220 or 230 with the pressure cap it will puke coolant at anything over 212 and maybe below that with a no pressure cap but it won't run cooler it will just boil over.

 

Gene-Kooning. I seem to keep running around 220 with the needle still climbing so I just shut it down. It’s a fresh rebuild. No boil over but I wasn’t putting the cap on either

 

Jalopy-joker. It’s running 220 after maybe 8-10 minutes of running. So I just shut it down. No boil over tho

 

Petejoe. 220? Needle keeps climbing so I just shut it off

 

What engine? What mods? What thermostat? What kind of car? What radiator/shroud? Where are the pics??????????

.bjb

 

Steal your wife's candy thermometer ( or any good liquid thermometer,) & check the fluid tempo . You can also use an infrared heat gun to check the rad & thermostat housing . put the cap non & if driveable drive it or if not driveable put a good box fan in front of the radiator & test .Make sure the stats in right side up . Try a different stat .

 

2old2fast I’m on my second stat already. Went from 185 to 180. Without the stat it runs 160 all day long

 

Jokester. It’s a 1954 Hemi just rebuilt bored 30 over. That’s it! Everything else is original. Recored radiator, it’s huge! Original shroud. Fan is moving lots of air in the right direction. It’s on a C1 truck. Stat is 180. I tried 185 and had same heat issues. Runs 160 without the stat. I gotta be missing something!

 

Rebuilt engines run hotter until everything has loosened up / bedded in, whatever you want to call it. 1000 miles with no wide open throttle or lugging / laboring and the picture should be different. 220 is getting very warm but nowhere near terminal.

How's the timing??

A belt on the waterpump helps too!!!!!

Chris

 

Have you boiled the stat to confirm its opening? If it ran 160 all day without a stat, that could be an issue.

 

If this is your problem driving down the road, you do not have enough radiator. If it is the problem sitting in the driveway idling, then you do not have enough air flow (fan) across the radiator. The engine is generating more heat energy than the radiator is capable of rejecting to the air at the given conditions. The temp will continue to rise until there is enough temperature difference between the coolant and ambient air to reject the same amount of heat energy that the engine is adding to the coolant.

No amount of dinking around with thermostats or caps is going to change these basic laws of thermodynamics, assuming everything else is correct.

I wonder if that is the correct thermostat? The reason I am asking is, as the stat that you have pictured opens, the bottom half is supposed to block off the bypass line. That type of stat was often employed in later model cars and may not be correct for your '54 Hemi. It may be preventing the stat from opening correctly by bottoming out in the housing, and hence why you don't have a problem with the stat removed, but do with it in.

You may need the style on the left.

 

There is no belt in that picture!

 

Drill a 3/32 hole in the flange of the thermostat. This will allow for steam, and any remaining air to escape.

I have seen engines with air in the block make steam pressure behind the thermostat without opening it. One little hole fixed it.

 

I would get something like this, it's a shorter stat and has a jiggle valve in it.

 

Happy daze. Ha! Yup have a belt on water pump! Timing set to the manual and I’ve played with it a bit. Between 4-7 btdc

 

Gimpyshotrods. Yeah I know. I didn’t have my glasses on so couldn’t see all the detail. It does now. Ha! Good eye

 

Voh when it first got hot with the 185 in there I pulled it and it boiled at 185 but it didn’t seem to open in the truck. Radiator was nice and cool

 

That will make an engine run really hot, really quick.

Anyways, try drilling that hole in the thermostat flange.

 

FrozenMerc. Good points!

 

That Summit photo is not a high flow unit for a MOPAR. I use one in my Y block they have the same outside diameter.
With a heat gun check the temp before the thermostat and after should be the same with a high flow, top of the radiator and at the bottom, there needs to be a drop in temp.

A check when cold.. have the coolant down 1” in radiator, start engine with cap off, keep watching for movement of water, when your sure the thermostat is open you should see coolant moving, if not slightly raise idle, if there is now coolant moving you need a smaller water pump pulley.

I think I saw Teflon tape on your water temp sender. It need to be grounded. Check with a meter. If not, remove the Teflon from the lower half of the threads; the top half will seal the coolant.

Ground the engine to the body and to the frame. 2 separate grounds..

good luck.

 

This^^^^ If the thermostat isn't submerged in coolant it won't open, use a known good gauge or infrared thermometer while warming the engine, when the thermostat opens you will see the temp drop slightly, then increase again .
+ new engine / breaking in as stated previously will run hotter.