The Quick/Small/(Stupid?) Question Thread.

[C.Costine]

I happen to have my radiator and overflow tank out as part of my head rebuild and timing chains and sprockets project.

Can someone explain to me how the radiator pressure system works on the roadster?

it seems to just have a cap (no pressure releif valve) on the radiator and then has a hose that goes from the middle top of the radiator (not the cap) and is unregulated presumably and runs to a metal overflow tank, it enters from the bottom but then there is a push button on top of the overflow tank's pressure cap that when pressed would maybe allow pressure out of an overflow tube at the top of the bottle and runs it down to under the roadsters engine bay. that would allow opening the pressurized cap for toping it off. that reservoir tank's cap also is spring loaded and rubber sealed and would release if there was too much pressure as well and allow fluid or air out the overflow dump hose.

so it appears that the metal overflow tank is pressurized?
that would be different than all my other vehicles I have ever owned.

so does the overflow tank run all the time pressurized evenly with the radiator pressure?

how many pounds of pressure does it run at?

im guessing it is critical to have a well seamed overflow tank, it seams horizontally in the middle. I think mine has a leak but I have never noticed an issue with it in the past with loosing water. I have also never noticed the overflow tank having any pressure but im not sure I ever checked it hot.

im trying to decide if I need to get the seam brazed as I think it leaks. if I do I will need to repaint it too but I should get that done before reassembling everything.

it will probably cost more to braze it than the tank is worth!

or are there other alternatives to use to seal the seam on the tank?
maybe running a bead of JB Weld on it?

All of my other vehicles except for my antique tractors have a coolant recovery tank which is under the same pressure as the cooling system, which then comes under vacuum as the engine cools off, and the coolant gets sucked back into the cooling system. My tank was leaking, it was not brazed it was just soldered. I just heated it up, got it apart, cleaned it up good, and soldered it back together.

[svwilbur]

For the 4 years I have owned the roadster I am assuming that it has had this leak in the overflow. I never had an issue with it over heating or getting at all hot or losing water as the air leak is at the halfway point of the tank where the seam is. And I guess I have kept the level below that. The main radiator has always been full when I check it cold.

So what negative happens as a result of having an air leak in the recovery tank?
Does it make it boil at a lower temp or something as a result of less pressure?

[fj20spl311]

Maybe!
You need to check to see if it holds pressure.
Many times a seam leak will seal under pressure and only seep after the pressure is removed.

[pebbles]

So what negative happens as a result of having an air leak in the recovery tank?
Does it make it boil at a lower temp or something as a result of less pressure?

yes, if it isnt holding max pressure it will boil at a lower temp.
Also, after driving, as the engine cools, it draws the water from the tank. If there is a leak it might draw air. You may end up with an airpocket in the block, radiator hose, or waterpump.
Most new autos have a HOT/COLD line on the clear plastic tank.

[mraitch]

I think it all has been explained - but to be clear. (Others can always chime in)

The pressure in the system is controlled by the cap on the overflow tank (and I don't know what that pressure limit is - probably 7-13PSI)

The cap pressure on the 'tower' is 'fixed' - merely a place to introduce coolant (BTW NEVER use the overflow tank to TOP off the coolant - ask me how I know) - when the coolant heats up it expands into the 'overflow' tank - perhaps not the best word (expansion would be better).

When the engine cools down, coolant is sucked back from the tank into the overall system. (Thus it is important NOT to have the tank FULL - half way at cold seems to work)

Thus when COLD - the level in the coolant tank should not have significantly changed.

If it is significantly lower, then coolant has gone somewhere. Either the engine is running too hot and pushing coolant out of the overflow tube, or there is an increase in internal pressure - (exhaust gas getting into the system (head gasket)) or there is a leak somewhere.

Personally, I think this is one of the most effective systems, over a pressure cap on the radiator, since the latter merely expels coolant into the outside world, and there is no indication of internal issues. Clearly IMHO.

Any breeches/leaks in the system - hoses, heater system, freeze plugs in the block or the intake manifold (again ask me I know) will compromise the pressure/amount of coolant in the system, impede the natural flow of coolant and likely compromise the water pump (again ask me)

FWIW

[greydog]

Does Jim(JT68) have a wesite where I can see all his products?
Dan

[svwilbur]

Does Jim(JT68) have a wesite where I can see all his products?
Dan

I am not sure about that but he does have 20 posts in
New Reproduction Parts
http://www.311s.org/phpBB3/viewforum.php?f=61
just look on the left to see if jt68 created the post.

and he also uses ebay some
http://www.ebay.com/usr/jt68
you can go there and click on "items for sale" link or contact him through ebay.

and you can send him a PM or email from 311s as well.

[cktrap]

Just contact him and ask what your looking for. Great guy easy to deal with.
Keith

[greydog]

Occasionally, I enjoy looking at Datsun Parts site just as a sort of daydream.
Jim offers many cool items. I was wondering if theres a catalog where I can scan thru and dream.
Dan

[car_cursed]

Does anyone know off hand the length and thread pitch of the stock fuel pump studs for the 310?

[car_cursed]

Does anyone know off hand the length and thread pitch of the stock fuel pump studs for the 310?

5/16 x 18 FYI.

[svwilbur]

What is the correct way to install a temperature sender on a 1970 U20?

I had issues with the temp sender the PO installed. He added a ground wire on the retaining nut to try to make it work better but that did not help. I checked the guage and if I ground the sender wire the guage goes slowly up to full hot so I think the guage is ok and the wire.

I have a new temperature sender to install as I am putting things back together after changing out timing chains, sprockets and tensioner stuff and shims and a rebuilt head and painting the engine bay.

so I took the old temp sender out, cleaned its housing, threads and the base ring where the sender pushes against it. and cleaned corrosion and dirt build up around where the sender base cylinder rides.

but when you assemble the sender part, is it just done bone dry?

I know when assembling the housing to the head you need use a gasket that has metal ground chip in it on the head side of the housing.
I have heard you need to use sealant on the gaskets but not on the sender area?

I have heard in the past that using sealant around the sender will often make it fail to work as it may insulate the sender from the housing ground through the block.

So around the sender no sealant?
no teflon tape?
nothing?

what keeps the sender from leaking?
just the pressure of the brass base against the aluminum?

how much torque do you put on the retaining nut?

how much torque on the nuts for the studs that hold the housings together?

any other suggestions?

[JT68]

Teflon tape or antiseize on the nut threads only. The tapered seat creates the seal.

You can also put an aluminum crush washer in there as well if you can find the right size, but typically not needed.

You could also use a very thin film of gasket sealer on the seat, but you would want to keep it to a minimum.

There is a lot of metal-metal contact, so you would have to go overboard with silicon to fail that.

Just hand tight on the nut, so maybe 5-8lbs or so. (tighten a little more if it drips)- don't overdo.

Hand tight on the 8mm nuts, 8ft-lbs would be fine if using antiseize. Hand tight with a short wrench.

The housings often get broken when/if the thermostat slips out of the groove during assembly (couple small dabs of silicon will prevent that) j

[svwilbur]

Thanks Jim (JT68), for all of your help during all these various protracted projects!

I am getting close to initial fire up for the head gasket.. I just have this sender and thermostat, the intake and exhaust manifolds, carbs and fuel line, and oil pan and oil left to go. maybe get there by Monday or Tuesday if my schedule permits. it will be interesting to see what ends up needing more attention as everything under the hood was touched as a result of taking stuff off for cleaning, painting, wiring or replacement /refurb etc.

[svwilbur]

is SAE30R7 the correct type of fuel line for our stock engines in roadsters?

I have some in my roadster and some of it has gotten hard so I am going to replace it. I was wondering if there is anything better that does not harden over time?

I think all the fuel line was replaced about 6 or 7 years ago.
the stuff going up to the fuel filter is fine but the stuff from the stock fuel pump that goes around the front of the engine to the.carbs on my 2000 has somewhat hardened.

my thought is that it is closer to the engine and heat maybe hardens it.

anyone else notice that?

any brands better than others?