Have read most of the threads and haven't found answer to my problem-not enough hot water flow through the heater core to warm up the car properly.
The engine heats up properly-the temp gauge reaches the correct temp in the normal amount of time. The engine coolant is hot after warm-up. I have removed the valve located in the heater core supply hose and installed a bypass (short piece of copper tube) to verify this is not the problem. I have reverse flushed water thru the heater core with a garden hose. I have bled the air out of the system.
The lower heater core hose does not heat up properly unless I race the engine. It seems like the water pump is not pumping water through the heater core properly at low engine RPM.
I have run the diagnostics on the digital heating system and all is normal(I can post how to do that if anyone needs it - it's simple to do but takes a lot of describing).
What is my problem?????

 

someone recently mentioned their problem was fixed when the dealer did an "air bound flush" for their heating... ...they said it fixed the heating...i dont know how that is done but if someone knows i would be interested.

 

You may still have air in the system. I'm not sure on how to bleed the VG. Since you said it the engine temp heats up like its supposed to i guess you could rule out the thermostat. I was having similar problems with my heat and last week i did my water pump(VE, was leaking), hoses, and thermostat for preventative maint' and now my heat works fine. I think the souce of my problem was my thermostat. It wouldn't close all the way and it took longer for my car to heat up. You may also have a clog in your heater core somewhere. They have some cooling system flush solution that you leave in your car for about 600 miles before you flush it i'd try some of that too.

 

Martin, I too have a 90 SE with the electronic climate control that only blows warm (if that). I can't offer an explaination to your problem, but I will take you up on that diagnostic offer for the climate control. Either post or PM me. Thanks.

 

I was actually prepared to use some of the cooling system flush, 'til I read here in a post that using that stuff was harmful (not helpful) to our particular situation. Anyone care to elaborate further on that situation with some insight?

 

Ok, based on my weekend in the garage under the hood with lots of time to think about all things automotive, I would offer that an "air bound flush" simply means the system was air bound (ie: full of air) and the air was bled with a flush and refill, being careful to let the air out completely.

The best technique I found to get all the air out was to get all hoses hooked up properly except the upper rad hose. This I attached at the engine, but with the rad end pointing up. I filled the engine slowly thru this hose to fill the top of the engine and thru the rad to fill the bottom(plug the the rad inlet hole with a rag), until I got fluid exiting at the bleeder hole on top of the engine. Getting all the air out is essential for proper water flow through the system, especially the heater core since is has such small tubes.
Install the upper rad hose, screw in the bleeder half way and warm the engine up until all the air bubbles finish exiting. Takes 5 -10 minutes, with the engine racing, to promote fluid circulation. The heater works better but still cools off when idling at slow speeds.

Hope this helps.....

Martin, '90 SE 5spd

 

You have to run the engine over 3000 RPM on the road... then the heat works great. That means 80mph+ or run a lower gear. Seriously: when I do an acceleration run I get blasted with heat.

Same issue... with a manual unit. It's usually warm enough for NC, but takes a while to warm the car. Haven't messed with it.

I wonder if putting the front end up would help (ramps/stands) or maybe just on the right side while filling system like the last poster suggested. (Sorry, thinkin' too hard)

 

I had the same problem crop up when I did my water pump, timing belt and thermostat last year and I have gotten it a little better through constant and anoying bleeding of the system but I never got it back up to the way it was before and a friend of mine who works for a Nissan DLR stated that it is very hard to bleed the system unless you have some sort of tool they have that sucks all of the air out.

 

Could u ask your friend what that tool is called?

the name would be useful if i visit the local nissan dealer here...or they might try to have me bend over and tell me "oh gee your heating system is screwed up BUT we MIGHT be able to fix it...but its gonna be $500 for the labor and the special tools required and the specially qualified technician we'll have to call in (who happens to be the only person in this world who can operate it) from our techical center in the Arctic where they developed the tool for those winters there and also cuz we're doing u such a big favor cuz where would u go if it werent our TOOL to help you in this winter........

 

I didn't spend time reading the posts, but i would check to see if the blend doors are stuck and are letting in some cold air with the hot air. like i said I didn't spend time reading, but if all else fails.

 

The blend door is not open - this I verified by watching the motor operator move it from fully open to fully closed while in diagnostic mode (digital heating system).

The problem simply stated is: there is not enough water getting through the heater core to replenish the heat that is taken out by the blower. If the blower is off both hoses heat up properly; the moment the blower moves air over the heater core there is not enough flow to keep ahead of the heat removal and the exit water feels cool - because it is.
The $64 dollar question, then, is why is there not enough flow??
It's either the water pump or the heater core or something in between.

I should add that I have done coolant changes before without any special regard for how the system was filled. I do always open the bleed screw to let any air out, however.

 

sorry to be of no help, but I have no idea, sounds like your guess is as good as mine. Good luck

 

Replace your radiator cap, had a similar problem when my water pump was leaking, after replaceing the water pump air was getting in, replaced the radiator cap and heat was blowing hot at all times when engine warms up