Question about cooling system and heater core

[Eikon]

I have problems with my RB20det overheating.

I had a pressure test done, so it apparently is not a head gasket.

I had a new radiator installed, so that shouldn't be the issue.

I put a new thermostat in... so that should be OK.

I beleive it is the water pump that is the problem... I just don't think it is pushing any coolant through the engine... I don't think there is any flow.

The other day I was driving it to the mechanics (Will soon be doing water pump), and noticed that I was getting NO heat from the heater. Keep in mind, it's very cold here. The temp gauge began to climb high.... still no heat!

I shut it down on the side of the road and opened the hood. In freezing temp, the engine cooled down pretty quickly. Then I turned it back on and wouldn't you know.. I got heat out of the dash... but only for a few seconds, then it sort of ran out and went back to cold/mild air. Had to shut it down one more time to be sure not to get it too hot. Then turned back on, and got heat.. but only for a few seconds... then cold air again.

Is this a sign that I am not getting any flow of coolant through the engine? Does this back up my water pump guess? Is my heater core stuffed up?

I don't understand why I would get a little heat only at start-up, and then have it go away again very shortly after.

My finger's are crossed that the water pump will be the solution.

Please let me know what your thoughts are on the heater issue.

Thanks

[Craved]

was your radiator getting blocked up? this could have also happened to the heater core, low flow through that core would explain the heat at first then cooling off as there is no hot water passing through it to heat the air up again!

as for overheating... usually a water pump would leak through the front when the bearings go.... it may not be the cause..

have you run a flush through the system to clean it out?

[blind_elk]

Have you checked the thermostat is operating properly?

Have you run a diagnostic on the A/C system?

You can check for water movement by running the engine at idle (at operating temp) without the radiator cap, and then revving the engine - you should see water moving across the filler neck of the radiator.

[Eikon]

Have you checked the thermostat is operating properly?

Have you run a diagnostic on the A/C system?

You can check for water movement by running the engine at idle (at operating temp) without the radiator cap, and then revving the engine - you should see water moving across the filler neck of the radiator.

I have not done a full system flush as I am told that is very expensive to do. Though I may have been given poor info.

The thermostat is new, and has been tested to open at the correct temp.

There is no A/C. The RB20det is swapped into a US model 240sx convertible. With the droptop, I have little need for A/C.

I will try with the radiator cap to see what I can see.

I am sure that the heater core is stuffed, as the radiator was so much that it needed to be replaced. But, if it was stuffed.. why would I get even a little... I would think I would get no heat at all?

Thanks

[Craved]

the heater is probably blocked but not to a point where no water goes through.

hence while it sits there it is able to heat up the core, but once the cold air is pumped through it it cools it down and the amount of water flowing through it is not enough to maintain temperature!