Datsun Roadster Forum-311s.org

I'm driving my '65 SP310 in earnest now that she is road registered
We are experiencing days of high 30C and my cooling system is only just coping.
The '65 has a low pressure system, 7psi, and no recovery tank.
What I am thinking of doing is adding an expansion tank connected to the radiator overflow tube, fitted with a 7psi non recovery cap and fitting a blanking cap to the radiator.
Still a low pressure system but able to vent and siphon/recover coolant instead of weeing it on the ground
Has anyone done anything like this and can share any design they used?

BTW, what dictates that a cooling system is low pressure, 7psi[50kpa] as opposed to high pressure 15psi[90kpa], apart from the rating of the pressure cap?????
I was advised NOT to fit a 15psi recovery cap to the radiator as the "system" was not designed to run at that increased pressure.
Why?
What is the criteria, Hmmmmmmmmmmmmmmmmmmmm?

P.S. Apparently a long neck 7psi recovery cap doesn't exist, I would have to replace the long neck on the radiator with a short neck design and use a short neck recovery cap.

When I had my 1500 it would run hot. I had them change the core to a 3 row truck core and the problem went away.

I also cleaned up all the waterway passages on the head and block to remove any casting material restricting the opening between the head and block. Used the head gasket as a guide on how much to open them up.

Great to hear the car is on the road!

Have you considered simply copying the later cooling system expansion tank?

I'm trying to think of why NOT to go to a 15 psi cap. The 1500 shares so much of the same parts. I mean, the hoses are the same construction. The only thing that would concern me would be the heater core as the weak link...although 15 psi is squat when it comes to pressure in a brass tube. The pump seal would have to work harder but the pump itself wouldn't care...it's about differential pressure not total pressure.
7psi to 15psi from a mechanical strength standpoint is really insignificant. But maybe there's a component in there that can't take it ??

GeoffM wrote:Great to hear the car is on the road!

Have you considered simply copying the later cooling system expansion tank?

I'm trying to think of why NOT to go to a 15 psi cap. The 1500 shares so much of the same parts. I mean, the hoses are the same construction. The only thing that would concern me would be the heater core as the weak link...although 15 psi is squat when it comes to pressure in a brass tube. The pump seal would have to work harder but the pump itself wouldn't care...it's about differential pressure not total pressure.
7psi to 15psi from a mechanical strength standpoint is really insignificant. But maybe there's a component in there that can't take it ??

Copper head gasket?

Curtis wrote:

GeoffM wrote:Great to hear the car is on the road!

Have you considered simply copying the later cooling system expansion tank?

I'm trying to think of why NOT to go to a 15 psi cap. The 1500 shares so much of the same parts. I mean, the hoses are the same construction. The only thing that would concern me would be the heater core as the weak link...although 15 psi is squat when it comes to pressure in a brass tube. The pump seal would have to work harder but the pump itself wouldn't care...it's about differential pressure not total pressure.
7psi to 15psi from a mechanical strength standpoint is really insignificant. But maybe there's a component in there that can't take it ??

Copper head gasket?

Yeah, I thought of that as well but we're talking miniscule pressure compared to the torque on that gasket and the pressure it is designed to seal at the combustion chamber. Look at banjo bolt gaskets. I dunno...

GeoffM wrote:

Curtis wrote:

GeoffM wrote:Great to hear the car is on the road!

Have you considered simply copying the later cooling system expansion tank?

I'm trying to think of why NOT to go to a 15 psi cap. The 1500 shares so much of the same parts. I mean, the hoses are the same construction. The only thing that would concern me would be the heater core as the weak link...although 15 psi is squat when it comes to pressure in a brass tube. The pump seal would have to work harder but the pump itself wouldn't care...it's about differential pressure not total pressure.
7psi to 15psi from a mechanical strength standpoint is really insignificant. But maybe there's a component in there that can't take it ??

Copper head gasket?

Yeah, I thought of that as well but we're talking miniscule pressure compared to the torque on that gasket and the pressure it is designed to seal at the combustion chamber. Look at banjo bolt gaskets. I dunno...

Don't a lot of people just switch from the copper head gasket due to cost and availability to the 1600 one?

Curtis,
Everything is new and fresh with an R16 head gasket.
I got a quote on a 3 row radiator core and decided I couldn't afford to sell another kidney
GeoffM
Thanks, I'm enjoying the current "shake down" cruise
"Have you considered simply copying the later cooling system expansion tank?"
That is essentially what I have in mind but in a stealthy manner.
I'm interested in any points of view re 7psi V 15psi.
I will discuss it again with my Radiator man but it has me very inquisitive atm

What I am suspicious of, is that the temperature sender, although now the correct type for the 1500, may be reading pessimistic.
After all it is immediately adjacent #1 exhaust port
I am in the process of fitting a CHT to spark plug #1 to cross check to the gauge readings.


Once I determine if it is lying, I'll re-calibrate the gauge to read more accurately.

I would still like to go to a recovery system though

Ive determined my sensor is also very pessimistic, lol. Ill be keeping an eye on this thread to see what you come up with. I was trying to find the post that had a how to on recalibrating the temp gauge but cant find it. I think maybe ted heaton was the OP?

It should only be a matter of adding a trimming resistor either in series or parallel with the sender
I have already done this mod to a late model Fuel gauge to make it work accurately with the SP310 tank sender.
That works just dandy

I remember reading something about 2 small holes in the back of the gauge and using pick tools to adjust the needle position?

Maybe my situation is slightly different. I am not overheating, temp at sensor is between 180-190 degrees However needle will peg to full hot once warmed up....

I'm not convinced my car is overheating either but until I get an independent temperature reading I am unsure.

Agreed! Best to verify for sure. It seems that a lot of 310s have this issue. Btw, very happy for you getting to drive your car! I think i know how you feel and your heading into summer! Lucky you

I also wanted to say that you have been a great help to me with getting my car back in order. Your contributions, handy pictures, and overall knowledge of these cars rock. I always look forward to 310 specific posts since they are different enough that much of the 311 info doesn't apply. Thank you!!

Toptech360,
thanks so much for your kind words, I try to pass on my experience, both good and bad!

The weather is really warm atm, we have broken records for October temps.

The only wrinkle with driving the Roadster, is I have to fill out a Log Book for every day I use it.
Not a big inconvenience but a legal requirement.
The bonus is I get a reduced rate on Historic Registration but I am limited to 90 days travel per calender year.
I'm happy with that

I added a coolant recovery tank to my 1964 1500.
I should not show pictures as it is not stock/correct BUT
it sure is a useful hot weather driving improvement.

The early no recovery coolant systems depended on the radiator finding its own level that
allowed for coolant expansion space in core. For my 64 1500, this worked fine for most conditions
but at 70 mph and 100 degree weather the "level" was about half!. Lots of coolant spit on the ground.
The 1500 roadster engine room has the same space for the recovery tank as the later roadsters.
Added the recovery tank and caps as shown and it works like a "modern" car!.
The tank would not be so obvious in its stock black but I like the brass.

The roadster water temp and fuel gauges are adjustable. There are small openings in the back and
a small "wheel" can be turned to adjust the gauge needle. My motor temp was average when hot but the needle was off
the scale and buried behind the opening!!. Adjusted the needle down to read in the middle and no more "Boiling" temp readings.
The adjustment is difficult with the gauge in the dash and as they are likely the original gauges the adjusting wheel is
likely stuck but can be loosened with a carefully applied small amount of spray lube.
I adjusted my 64 1500 gauge in the dash but used a spare gauge
to practice the technique and you need to make a properly bent pick tool to turn the wheel. Run the motor till it is hot and
adjust the needle to where you want it to read at normal operating temp.
Our Gauge GURU, John Frampton, provided guidance for this adjustment.

Ted.

Many thanks Ted!
I'm learning all the time

So is the radiator cap a blank type and the overflow cap the pressure cap?
What pressure are you running in the system?