Coolant 'overflow' when not overheating.... what's up?

On 'Otto', our '60 Bugeye, 1275 eng, mostly original other stuff....

So, I've replaced all the hoses, and what I thought was a 'leak' doesn't seem to be. Here's what it does...

I filled the radiator with the car cold (I know it says to do it hot, but how do you safely take off the rad cap when it's hot?) I filled it until I could see the fluid in the 'throat' of the inlet... if that makes sense.

I start the car, look underneath... no leaks. I drove about 10 miles on a warm day... 80 ish degrees... no leak, temp nice at 190. Sitting in traffic for the next couple miles temp rose to over 200, maybe up to 210 ish. I got where I was headed and looked under the car while running... no leak. Shut the car off and went inside for about 5 minutes. Came out and there was nice puddle running out from under the car. Nothing was spraying... no fluid up on the rad, engine, hood, fenders, etc... just on the ground. Drove back to my office, less traffic, about 6 miles... car cooled down on the open road to 205-208.... may have gotten cooler if I had more places to go.

Pulled into my office, left him running and looked... again, nothing leaking. Shut it off, and waiting... no leak or overflow.

So.... did I overfill the rad? Or is the cap letting the pressure out too soon? I do have the correct deep rad cap, as discussed in other threads.

Thoughts?
Thanks!

So is it the 948 radiator?
if so it takes a cap with a longer reach to seal
when it warms up it over flows
check the cap reach and make sure it is the correct one

I will also say that these thing burp inexplicably from time to time as well

It's the correct cap... we checked that out when trying to get him to run cooler. And yes, I believe it's the original 948 radiator.

I thought maybe a 'burp' made sense, but the weird thing is that the drive I took is one I take every week on the same day... same route. Office, bank, printer and back to office. It's happened twice while I go into the printer.... strange.

How to do you guys make sure the coolant level is right without scalding yourself? Do you follow the book and check while hot or just fill it till you see it in the inlet like I did?

As a side note..... How fun is it do go thru a bank drive thru in a Bugeye? Smiles from the tellers when I have to reach up to put stuff into the carrier!

Refresh my memory... Is the temperature sender in the head or the radiator.
Honestly, the car shouldn't be going over 200 degrees with casual driving.
If everything is properly in tune, I would replace the water pump with a high quality unit and install a new radiator (probably a chinese made one that they sell on ebay). At the same time I would flush the block. If the problem persisted I would remove the head and try to clean as many water passages as possible.

After filling the Rad it is best to run the car to operating temp to burp the block. This is to insure that you have all the air out. Just run the car without the cap on the rad until air burps out of the rad. Let it cool and then refill till you see a bit of coolant in the neck. You probably have some air trapped in the system that expands with heat soak after you turn off the motor. It forces coolant past the cap and then into the overflow line.
When filling make sure the heater outlet is open, this helps to prevent air from being trapped in the back of the block
I agree that a 1275 with a downflow rad should not run above 200. I have the same setup and I run a steady 190 in NY summer. Make sure that your rad is properly shrouded before going with new bits. if the air has a path around the rad it will take it and not cool.

Maybe a small expansion tank would help?
Works for me

Mm not sure what the issue is with the picture upside down
I have a small tank stainless steel mounted on the side of the radiator

Good point about the shrouding. The early bonnets had no shrouding and many fiberglass units do not have any.

Trevor
I dropped the operating temp at 65 Mph by 10-15 degrees by adding some aluminum aroind the nose plus some foam to seal against.

Ok... so I took a look under the bonnet and there is shrouding in place, though perhaps not sealed up as well as it could be. Also, I'm guessing the 948 had an air intake that lead via hose to something mounted directly in front of the battery... something that the 1275 did not need... thus, the hole is wide open on that side of the grill, which must be sapping some of the air from going thru the radiator.

That should be plugged up, correct? What was it originally connected to?

I'm not sure you have a problem.....If you fill the radiator up to the neck when it is cold, then when it gets hot, the coolant will expand. The expansion then causes the cap to open and it runs down the tube and out the bottom of the car. A puddle!! The trick that I found was only fill the radiator up to just cover the tubes in the upper tank. That gives plenty of room for expansion, and less pissing on the ground.
Cheers,
Scott in CA

Mike
"the something directly in front of the Battery" is the heater. There also should be a fan unit adjacent to the heater box. There is supposed to be a hose from the air intake in the grill to the heater to supply fresh air.
As you are not running this hose , there is a good bypass of air from this opening. You can Duct tape over the opening and see if there is any difference.
Yes, there is some shrouding in the nose to the rad. The issue is does it seal to the rad or will the air just go around.
In jolly old England where it is usually (except this summer) cool there is not much of an issue. Have a look the big Healey board and all the issues with the Rad shrouding on the 100 series cars.
Remember BEs were designed in the late 50ies and there was not a lot of stop and go traffic. The cars were supposed to be driven on winding English roads

Scott
If you continuously are pissing out the rad tube something is wrong. The BE rad uses a 7 pound cap which means that the coolant temp will be about 230 when it pops the seal.

Thanks for the info.... makes a lot of sense. That heater vent opening would surely pull a ton of air away from the rad. I'll cover that and find ways to seal the smaller gaps and holes and see what that does on the next warm to hot day.... hopefully that'll fix it.

So if the temp had to hit 230 to pop the cap..... that means either my gauge is low or the cap is weak / wrong. It showed maybe at the 212 line, but def. not above. And again... it did not overflow until a few minutes AFTER I shut down the car. Seems like it would have started cooling right away... not gotten hotter.

The water in the rad probably starts "cooling right away" but not that in that big hot lump of cast iron.

Bayless said:

The water in the rad probably starts "cooling right away" but not that in that big hot lump of cast iron.

Click to expand...

Right... but likewise, the block should also not get hotter once the engine is shut off. It might cool down very, very slowly, but it shouldn't increase in temp. Yet ..... something makes the coolant overflow momentarily a few minutes after shutdown. And... only once.. then it seems fine... The evidence is anecdotal, tho... perhaps more occurrences would give more info...

Classic heat soak. With the engine running, the water is moving and you are taking heat out of the block. The block is much hotter than the water. You turn off the motor. Now water is not moving and it picks up the heat real fast. There is a big delta T between the block and the water.
The pressure temp and pressure of the water in the block goes up fast and could overpressure the cap for a second or two. also if there is any air in the block the air expands rapidly with heat soak and will burp the cap.

Yeah, what Joe said.