[Roadsters] 1500 Radiator Cap.

Mon Apr 6 15:18:57 MDT 2015

I also had overheat condition that developed originally developed over about 75 miles of driving, then eventually 50 then down to 25.  It kept doing the burping of coolant out just as described by Charlie and just couldn't go anywhere without overheat. 

I of course refused to believe it could be the head gasket because otherwise the car seemed to run just fine and passed a leak down test as well.  Once I finally decided that it could be nothing else, I tore the head off and it was very obvious that it had been seeping for some time when looking at the head bolts, etc…  A complete rebuild of the head was done and I used the ARP studs to put it all back together (which I highly recommend).

Guess what? it runs right on the money with the temps and creeps a few degrees higher when pushing it at 80 on the interstate but then it cools right off to normal just like its supposed to.

Sorry Charlie, but I think you have a head gasket issue and the only thing that solves that is to take the engine apart and replace the gasket.  Since you have been running this thing at nuclear reactor core temperatures, don't be surprised if you need new valve springs and some other stuff.  But it will be worth it as once done properly, the little engine will just behave itself and drive nicely.

Dave Sommers
Dive Hatteras LLC
www.divehatteras.com
703-517-3724 

From: Datsun Roadster List
Sent: ‎Monday‎, ‎April‎ ‎6‎, ‎2015 ‎11‎:‎46‎ ‎AM
To: Graeme S., Datsun Roadster List

I had the same issue on my 67 1600.  Problem was not anything to do with radiator or cap. (I run stock cap).  Problem was head gasket.  Exhaust gas getting into the coolant and over pressurizing the system, pumping the coolant out of the overflow tank and eventually overheating.  I had my head cleaned up, used a hi quality gasket and sprayed everything with copper coat before reassembly.  Problem solved and car has never overheated or run hot since.

Good Luck.

Roy H.

From: Graeme S. via Datsun-roadsters <datsun-roadsters at autox.team.net>
To: datsun-roadsters at autox.team.net 
Sent: Friday, April 3, 2015 5:03 PM
Subject: Re: [Roadsters] 1500 Radiator Cap.

Been through this recently.
My cooling system and engine are all fully reconditioned and I have no overheating problem, BUT, it was belching coolant just the same.
Now, bear in mind the early cars were designed for a low pressure 7psi[50kpa], non-recovery type system.
The cap is not easily converted to a high pressure13psi[90kpa], you have to swap the neck of the radiator to get the new cap to work properly.
Low pressure cap uses a long neck, high pressure cap uses a short neck.
All the research I did showed that there is no long neck high pressure cap :(
My Radiator Shop advised to retain the low pressure system because that was what it is designed for: what the weak link is I know not!
Anyhoo, I decided to fit a blanking cap to the radiator and plumbed in a pressurised aluminium recovery tank from the radiator overflow connection, using a low pressure long neck recovery cap [7psi], on the tank.
Works a treat and if you didn't look between the front cross member and the radiator core, you would never know :)
The system can burp all it wants but it is able to syphon it back in to the radiator.
I posted some pics. on the 311s.org site, have a look here: -
http://www.311s.org/phpBB3/viewtopic.php?f=3&t=23012&hilit=recovery+tank
The final version is at the end of the posts.

Regards,
Graeme S.

nissanman.shutterfly.com

On 4/04/2015 09:07, Charles Hubbard via Datsun-roadsters wrote:

 My 1964 SPL310 (1500)  has run hot since day one. It has a fairly pristine 3-row radiator core.  I live in the Dallas Texas, area, and  it gets pretty hot around here.  The stock idiot gauge steadily pegs on the highway at about 65 mph.  I put an after market gauge in which showed the temperature close to 290 deg.  Slowing down to 55 MPH brings the temperature down but it still runs at 275deg.  After running around town and turning the motor off, it often blows most of the coolant from the upper tank through the overflow tube.  It often vapor locks after it gets turned off.  I took my radiator to the local old school radiator guru today. He did a flow test and it was fine.  However, he noticed that my cap was pretty week.  He thinks my stock cap may only be a 3-4lb cap and suggested that I purchase a 12 lb cap.  .  He's thinking that that my roadster may be continuously be losing coolant when it gets pressurised and allows air into the system, which makes the car run even hotter.  A tighter cap would hold coolant better and help the cooling.  The temperature would stay lower, even under more pressure. The stock radiator caps are not exactly growing on trees, so getting a 12 lb cap to give it a try may not be obtainable.  The radiator shop says they can put a new cap assembly o the unit, but I hate doing that before I even know if it will solve my issue.  Does anyone know a source for a 12lb cap that will fit a 1500 radiator?  Feedback from those in the know would be appreciated.

.Charlie Hubbard

Flower Mound, TX
cehubbard at verizon.net

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