Aluminum Radiator issues?

[jayd]

I just replaced a brass radiator with an aluminum one and getting some weird temp ranges. First thing I noticed was that during the first heat cycle the temp would rise to over 210 then drop to about 185, then to about 195. I installed a new 195 thermostat and get the same results, first heat cycle goes from 0-210+ before dropping to about 195.

The temp fluctuates oddly compared to the brass radiator, with the brass it would hit 195 and stay there, with the aluminum it varies a little with driving conditions. Seems to cool ok.

I put an aluminum radiator in a 1937 Dodge pickup I'm building, it has a thermostat controlled electric fan. I noticed the fan didn't run very often but the engine temp was very stable.

[pro70z28]

Sounds like air pockets in the cooling system.

[jayd]

I ran it up to running temp a couple of times without the cap while setting on the drive, looked like the air was cleared out of the system. I've driven it several miles since then.

[Itoldyouso]

That's not the way to clear the air out. If you have a recovery tank you have a closed system. What you need to do is run the car for a while and do not open the main radiator cap, just refill the recovery tank. It will purge itself and suck only coolant back into the radiator. Also, make sure your radiator cap is higher than the rest of the system so the air will go to the highest point.

Reason I sort of know about this is we have run into the same problem burping the Olds engine in my Sons rpu. Whenever we would remove the radiator cap for any reason it would introduce air into the system and the car would immediately go to 230. But after it cooled for a bit and sucked the recovery tank almost dry it would never go over 190-200 again, and that was on a hot day (90+). All we would do is keep the recovery tank 1/2 full so it wouldn't puke and it cooled fine.

Don

[west_coast]

Sound like air in your system. See this link,
Erratic temperature swings | FlowKooler Automobile Water Pumps - Chevy, Dodge, Jeep, Ford, and more

I just replaced a brass radiator with an aluminum one and getting some weird temp ranges. First thing I noticed was that during the first heat cycle the temp would rise to over 210 then drop to about 185, then to about 195. I installed a new 195 thermostat and get the same results, first heat cycle goes from 0-210+ before dropping to about 195.

The temp fluctuates oddly compared to the brass radiator, with the brass it would hit 195 and stay there, with the aluminum it varies a little with driving conditions. Seems to cool ok.

I put an aluminum radiator in a 1937 Dodge pickup I'm building, it has a thermostat controlled electric fan. I noticed the fan didn't run very often but the engine temp was very stable.

[jayd]

It was air in the system, I had just installed a new thermostat and did not get all the air out. I removed a plug right next to the thermostat and that seemed to get all the air out.

[Itoldyouso]

Cool !! (Pun intended )

Don

[pro70z28]

Who would'a guessed.

[rspears]

It was air in the system, I had just installed a new thermostat and did not get all the air out. I removed a plug right next to the thermostat and that seemed to get all the air out.

I always drill a 1/8" hole in the T-stat and put that on top (Ford mounts vertical) in the housing to let trapped air out during fill. Works for me.

[sunsetdart]

On many motors, the sending unit for the gauge is located near the outlet to the top hose of the radiator.
What many do not understand is the temps you are seeing are temps of coolant that is leaving the motor, not what's in the motor. The coolant is at hottest point as it is leaving. So if the pump, fan, radiator are doing there job then the coolant temps coming in at the bottom hose should be 15-20 degrees cooler.

[Itoldyouso]

While we are on the subject of cooling, what causes a motor temp to rise when you turn off the engine? As an example, my Son Dan has a 455 Olds in his rpu and if it is running at 200 for example when he shuts it off to get gas or something, the temp gauge goes to 230 or 240 in a few minutes. I know there is something called heat soak, but I always equated that to a component like a starter absorbing heat from the headers or block.

I know that Olds has a lot of cast iron in it, but the sbf in my roadster will start cooling down the moment I shut it off. If it sits there for 15 minutes the temp will have dropped maybe 20 degrees.

Just puzzled by what is going on with his engine.

Don

[rspears]

Is Dan running aluminum heads, Don? The temp rise you're describing is caused by the residual heat stored in the mass of the heads, intake and to some extent the block, but to a lesser degree than the heads. When you're running you're in balance, with the heat generated by combustion flowing through the mass of the block and heads to be taken away by the coolant flow, cooled in the radiator and returned for more. At the momemt you shut down flow stops, and all of the heat in the heads & intake goes into the coolant that is trapped in the passages. Then when you start up your sending unit sees that spiked temperature of the trapped coolant until all of that hot fluid gets pushed out into the radiator. That's why systems with marginal cooling will "boil over" on shutdown, puking fluid into their overflow bottles or onto the ground - heat generated in the final combustion cycles is still moving into the metal, and nothing is being taken away from the coolant. Aluminum flows heat much faster than cast iron, better heat transfer.

[Itoldyouso]

Great explanation, thanks Roger. No, he is running cast iron heads and I am thinking aluminum ones might help somewhat. I do have aluminum heads on mine and and like I said, when I turn off the key on mine it starts cooling down right away. Of course, I am running a sbf and he is running a big block Olds, so there is a lot more cast iron mass in his.

One thing he is going to do is get rid of the SPAL fan controller and go with a simple relay and switch like I have so he can cycle the fan while he is getting gas, etc. The controller has never worked right and we have had a few conversations with SPAL tech dept with no fix yet. He is able to watch the fan blades while driving and sometimes the fan quits even though the temp is in the "fan on" range. He has even bypassed the on off range by running current to the ac wire on the controller (a suggestion by SPAL) but it still quits running sometimes when it is needed most.

Just a few new car bugs to work out.

Thanks again for that information, Roger.

Don

[TooMany2count]

Don, my 40 Chevy did the same thing and at times would puke.
What I did was add a windup timer switch into the circuit for the fan so I could let it run for 5-10 minutes after I shut the mtr down.
This in itself would cool the mtr down in the 5-10 minutes the fan would run, but I was running a hood on my car also. Which may have played in w/the cooling down since the mtr was in an enclosed area.......joe

[Itoldyouso]

Joe, that makes sense. Even my daily driver has that sort of delayed running fan from the factory. Sometimes I walk by it and the fan has come on all by itself, or sometimes it will run after the car is turned off for a while. When I first got the car I thought something was wrong and the fan was sticking on, but when I called the dealership they told me that is the way it is programmed into the computer. It senses that the temp has risen or that humidity is in the interior that needs removed, so one or several fans will come on.

So I guess even the car manufacturers realize the need to provide this sort of extra cool down.

Don