Datsun Roadster Forum-311s.org

Hello everyone! Yeah it's me....again. Lol. I replaced my thermostat, flushed out my cooling system with blue devil, burped it and it still gets up to *220 which is when my cars starts to run bad. But now my overflow is leaking and I think it as a hole in it. I haven't pulled it off and checked yet. So for now let's say it's ok.
Since we need a certain amount of pressure throughout the cooling system, how is any pressure even possible since the overflow tank has that opening/tube to let overflow out?
Why do we even have an overflow tank?
Why don't we just bypass it altogether to keep up the pressure and keep the flow circulating rather than going into the overflow?

The cap on the surge tank is the pressure cap. If your tank is bad, I have a spare

Natenate4s wrote:Hello everyone! Yeah it's me....again. Lol. I replaced my thermostat, flushed out my cooling system with blue devil, burped it and it still gets up to *220 which is when my cars starts to run bad. But now my overflow is leaking and I think it as a hole in it. I haven't pulled it off and checked yet. So for now let's say it's ok.
Since we need a certain amount of pressure throughout the cooling system, how is any pressure even possible since the overflow tank has that opening/tube to let overflow out?
Why do we even have an overflow tank?
Why don't we just bypass it altogether to keep up the pressure and keep the flow circulating rather than going into the overflow?

The tank that you are referring to is an EXPANSION tank.They came into use perhaps in the fifties when cooling systems became closed instead of open to the atmosphere. As the engine warms up and coolant expands, it has a place to go, instead of just running out onto the ground. Then when the engine cools the coolant that had been pushed out is drawn back in, and the cooling system is ready to go again. You need to check coolant only at oil changes instead of adding some every time that you drive. The over flow tube that comes off the top of the expansion tank is open only when pressure in the system exceeds that which the cap is made to hold. If the system overheats, pressure increases and if it goes above the max for the cap, the cap allows some coolant to escape out the overflow. When pressure drops back down the overflow closes back up. The tank is made of an upper and a lower half. most likely yours has a leak at the solder joint where the two halves join. If you can solder, you can heat it up and take it apart, clean, and re-tin the joint and solder it back together.

i'd do a pressure test on the cooling system to see if there are any leaks.
220 is over boiling - I would be concerned at that operating temperature.

Questions:
As the car warms up, are both hoses hot? Once the thermostat opens, boths hoses should be pretty hot to touch.
Once at operating temp, is the top of theradiator tank hot? How about the bottom of the radiator (no cold spots).
Have you verified that the water is actually 220 degrees? (maybe the gauge is way off)?
Are the heater hose (and bypass valve) correctly plumbed so that water isn't trapped?
Have you blown thru the radiator (or weshed it)? They can become plugged from plant (I washed a whole bunch of cottonwood fuzz out of the 1600 radiator fins).

How long does it take to get to 220? Does it happen at idle , on the road, at load only (like going up a seep hill)?
Once it's hot, can you let it idle and cool it off?

Dan

Some good advice above

Well for me, I added water wetter (consider blue ice in antifreeze instead of the red line product).
Have an electric fan in front of the radiator.
I have the larger 2 liter like radiator
And I still had some overheating
My fan belt got lose and I got a new alternator cause the pulley was loose (O'Reilly replaced it after 5 years FOC, a great place to do business if you can!)

Determined mine last overheat was from timing being retarded a little.
Timed it at 3000 rpm at the advance point and my heating issues are/were managable.
Have not driven since mid May.

Best burping method I've found is to raise the front end on jack stands and slowly
fill the radiator. I squeeze the hoses too to get the bubbles out. Got more in after it acted full on level ground.
After you can raise the backend too and add more to be sure it is full.

Sorry as none of this may be your issue.

Thanks everyone. I didn't know the coolent expanded. I was topping off the radiators and the expansion tank. So maybe it had too much. Spl310 I'll check it out better and get back to you. Thanks for the offer!
It'll idol and stay cool for a long time. BUT, once I get going it won't stay cool, then if I idol at a traffic light I'm screwed. Lol. That's the kiss of death.
I'll feel for those spots you mentioned and get back to you. I'm also going to get the timing checked out. I'll let more coolent out as well to see if I overfilled it

Need some suggestion for leaks in the expansion tank. Found the expansion tank that came with my '70 1600 had a leak. Tried to solder the two half's together but found two stress cracks in the side of the brass. Was not able to solder those and hold under pressure. Got a used tank on ebay and ended up with same issue with stress crack on side. Is this common failure? Any way to fix? Do I try another one from ebay or is there another new expansion tank that will fit the car (not original style).

I'd try a copper brazing rod ( have it done by a pro, but it may be shot ) should stop it ,check for a head gasket leak too . using a fill funnel to get the system completely full?
And a rod out or check

I have addressed this subject before sometime ago. It’s critical to the engine that the cooling system maintains pressure, at the atmospheric pressure of sea level water boils at 212 degrees F. If you go up to say 5000 feet, the temperature water will boil at drops to 202 degrees F. If you increase the pressure of the water in the radiator to .9 bar, ie 13 psi you raise the boiling temperature to about 245 degrees F. Note that the factory cap on your radiator has a .9 on it, meaning it’s a 13 pound system. You can’t assume the system holds pressure without verifying it. I recommend to everyone I work with that the buy a used Stant pressure tester on places like eBay or get a new one, as it’s a lot less expensive than an engine.
Other things that can effect overheating are radiators that don’t exchange heat do to blockage, lean fuel mixtures and incorrect ignition timing and advance curve. All important areas to be verified when chasing down problems related to overheating.
Dave

I have nothing to contribute except to say I learned some important nuances from reading the previous posts, so thanks for including that history... excellent discussion and info.

@RedSkull: If you’re not too concerned with keeping it OEM, there are plenty of options out there for new universal coolant expansion tanks.

Thanks for schooling us Dave, very thorough explanation. I knew pressure made a big difference but did not realize altitude factored in so much as well, makes total sense. (my Utah partner sites cannot draw as good vacuum because of altitude, and let's not even start with the extremely low humidity)
I was under the impression that ourselves (and Jag XKE's) were 7 lb pressure systems, and that is why it was so hard to find the correct radiator caps. (not in the typical Stant off-the-shelf inventory)
Perhaps that was just what was on mine when I bought it, so then thought I was replacing OEM unit with same rating replacement.
Thanks for the info.

How hot is in Utah in January?
The pressure makes a big difference in hot weather. but in even 50-60 degrees you should have the thermo nearly shutting just cruzing