'75 280z made it out of the garage.. briefly

[Neb]

Well I finally got my Z to (almost) ambulatory status. Unfortunately after about 5 minutes of idling and a very brief trip down the driveway and back, coolant started streaming out of the vent tube originating by the radiator cap. And continued for a couple minutes after shutting it off. 

Kind of a sad end to it's first self-propelled journey, but was curious if anyone had any ideas on why it would be dumping coolant. I don't think I had it running long enough to get anywhere near overheating. Is that where it would purge if I had maybe over-filled it?  Or is it possible that it did overheat after a couple minutes if idling..

I have also recently replaced the thermostat. And I also took the two coolant lines running through the firewall (I was assuming one was going into the heater core, and one was coming back) and just hooked one output into the other input so the heater core is omitted (picture included; had a leak somewhere above the passenger side floorboard and saving that for later).  I also just replaced the radiator cap.

Any obvious answers here? I'm worried I screwed up those lines. Or maybe something is funky with the thermostat.. or maybe I'm being paranoid and I just over-filled it. Thoughts?

Thanks!

 

[Patcon]

Does the temperature gauge work? What did it read?

Yes they can overheat quickly if there is a problem. Overheating these aluminum headed engines is a no-no.

[Zed Head]

14 minutes ago, Neb said:

 Unfortunately after about 5 minutes of idling and a very brief trip down the driveway and back, coolant started streaming out of the vent tube originating by the radiator cap. 

Kind of a sad end to it's first self-propelled journey, but was curious if anyone had any ideas on why it would be dumping coolant. I don't think I had it running long enough to get anywhere near overheating. Is that where it would purge if I had maybe over-filled it?  

 just hooked one output into the other input so the heater core is omitted (

I also just replaced the radiator cap.

Any obvious answers here?

The radiator cap is just a pressure relief valve.  If the pressure is exceeded the coolant is purged through that tube.  Could be that you got the wrong cap or that you just didn't have it inserted right.  Check that cap closely, make sure it's seated so that it can hold pressure.  If it's not seated the coolant will just flow out as it expands.

The heater cores are best if they are blocked, not connected.  By connecting them you're creating a short circuit for the coolant and it doesn't pass through the head.  It just circles around in that useless loop.  It reduces the overall flow through the engine.

Where'd you get that cool looking "FUSIBLE LINKS" cover?  Is that what they used in 1975?

[Neb]

30 minutes ago, Zed Head said:

The radiator cap is just a pressure relief valve.  If the pressure is exceeded the coolant is purged through that tube.  Could be that you got the wrong cap or that you just didn't have it inserted right.  Check that cap closely, make sure it's seated so that it can hold pressure.  If it's not seated the coolant will just flow out as it expands.

The heater cores are best if they are blocked, not connected.  By connecting them you're creating a short circuit for the coolant and it doesn't pass through the head.  It just circles around in that useless loop.  It reduces the overall flow through the engine.

Where'd you get that cool looking "FUSIBLE LINKS" cover?  Is that what they used in 1975?

Hmmm alrighty. I'll try the old radiator cap and see if it happens again. And I'll block that line; thanks for the input! I hope the 'short circuit' didn't cause it to overheat..

I 3D printed it ? want one? 

48 minutes ago, Patcon said:

Does the temperature gauge work? What did it read?

Yes they can overheat quickly if there is a problem. Overheating these aluminum headed engines is a no-no.

This is what I'm worried about. I need to troubleshoot the temp guage; it either isnt working or it didn't get hot enough to register. I think tomorrow I'll take it out and put it in some hot water while still electrically connected and see what I get. It's a new sensor so I was hoping it would work ? but I'm yet to actually see it register anything 

 

[Pop's Z]

I have found that when first starting up any work on the cooling system that it is preferable to use just plain water. Less mess and less coolant in the driveway. When everything is AOK then drain and replace with distilled water and the correct anti-freeze mixture. I had a freeze plug blow out on a fresh rebuild and was glad I just used plain water. Just my 2 cents.

Cheers, Mike

[siteunseen]

You could remove the radiator drain and run a hose pipe into the top of the radiator, balance the flow and let it idle for a few minutes to see if it overheats.

This is a 240 diagram but it should help.

[Neb]

Success!  I swapped out the radiator cap and that seems to of resolved the coolant purge issue.  Ran it for a good 10-15 minutes last night and didn't have any coolant leaks.  Also did a temp fix on that coolant hose to block the bypass for now. 

Also also took a quick look at the water temp sensor; still nothing on the gauge.  Pretty sure its wired up correctly.  Sensor is new.  More troubleshooting to follow..

Probably would have gotten more done, except I also changed the oil and had some serious difficulty removing the old oil filter.  And while I was at it, I got the oil pressure sensor swapped and functioning.  Good to see at least that gauge is doing what its supposed to ?

Definitely appreciate the replies!

[Zed Head]

5 hours ago, Neb said:

Success!  I swapped out the radiator cap and that seems to of resolved the coolant purge issue.  Ran it for a good 10-15 minutes last night and didn't have any coolant leaks.  Also did a temp fix on that coolant hose to block the bypass for now. 

Also also took a quick look at the water temp sensor; still nothing on the gauge.  Pretty sure its wired up correctly.  Sensor is new.  More troubleshooting to follow.

I think that you can test the gauge itself by grounding the harness wire at the sender to the block through a small resistance.  You can also measure resistance through the sender prong to the block to see if it's good.  The sender ground through its threads I think.  Sometimes people use Teflon tape and don't get the ground.

Found a procedure in the 1972 FSM -

[jonathanrussell]

On 9/3/2018 at 10:36 PM, Zed Head said:

The heater cores are best if they are blocked, not connected.  By connecting them you're creating a short circuit for the coolant and it doesn't pass through the head.  It just circles around in that useless loop.  It reduces the overall flow through the engine.

 

@Zed Head ..... I have read this many times also. I don't understand the logic though. Maybe you or someone else can help me understand. How is connecting these two and bypassing the heater core different from running the heat in the cabin and therefore having coolant flow through the core....essentially connecting the two hoses?

Thanks...

 

 

[Zed Head]

I think it's mostly the volume.  There was a thread very recently showing the inside of one of the water c ocks and you can see that it's a very small orifice, compared to the size of the water hose.   The volume through the heater core is small.  Connecting the hoses lets a large volume of coolant pass through the block then right back to the pump inlet.  Big hoses.  It would be like running a smaller water pump.  Plus the coolant is hot from absorbing block heat but doesn't pass through the radiator or the heater core.  So you end up with a large portion of the pump volume absorbing heat but not releasing it to the radiator.

Somebody actually did some dyno runs with temperature measurements to show the effect.  The infamous Tony D.  The engine got much hotter with the hoses connected, than with them blocked.