Question about 1990 Nissan Maxima

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I am not getting heat all the time into my 1990 Maxima I flushed the system and replaced the engine themostate. Water flows threw the heater coil. What is next?

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There are 2 thing is can think of right off the bat. Is the blower motor working? If your heater core and heater valve are working, is your duct valves working? They open and close using the car vacuum. When you shift your control to heat, you should hear the duct open or close. allowing only heat from the heater core. You may have a bad actuator valve or a leaking vacuum hose. That's all I can think of right now, hope this helps

Posted on Dec 29, 2010


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1990 nissan maxima. have replaced thermostat, but cant get any heat, or defrost. flushed out core.and replaced all fluids.

Check the hoses to the inside heater core for kinks. Check heater (not radiator) core for being plugged. Check heater valve to see if it lets coolant through when turned on.

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If the heater core bypass refers to the water flow to the heater core, I would wonder why you did not flush the heater core as part of the system. You can drain water from engine, disconnect heater hoses and add a short hose to the heater and force a garden hose to flush the core.

I have not looked up the particulars for which heater system is on your car. Some just use duct-work to close off air flow through the heater core and the heater core always has hot water in it. Others will use a valve to shut off the water flow through the heater core and they can be either electric or vacuum operated. Combination systems are the third system which controls water flow and duct air flow at the same time.

Some of the Premium Climate control systems with Electronic displays have a computer diagnostic system which self-diagnoses problems but you need the sequence codes and explanation of where the bad part is located.

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Coolant will not cycle threw the heater coil

its plugged, take off both heater hoses (at the engine) and hook up your water hose and try to flush it in both directions, water should flow easily both diretions. clogged cores are caused by coolant that is not protecting the engine.

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2004 nission maxima heater blows cold air engine coolant level is fine

If the engine is heating properly you most likeliy have a clogged heating coil or regulator (opens to allow hot water to flow thru the heater core. No hot water to the heater cord, not heat in the vehicle. Good luck

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Feel the 2 tubes at the firewall for the heater core. If they are not getting hot, the heater core needs to be flushed out or replaced. I had this problem with a 1990 Cadilac Deville, it was just a plugged up heater core.

Remember to install sealant after flushing out the system to prevent leaks.

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What is the easiest way to clean out the heater coil. I have replaced the radiator and the thermostat. Truck is not running hot, just not rcving heat in the cab.

Disconnect the heater hoses from the engine. Flush with a hose from your house attach it to one of the hoses turn the water on and let it flow for a few minutes. Turn the water off and switch the hoses and flush again. If you get good flow then the heater core may not be the problem. There are air baffles in the heater box under the dash that control which way the air flows. These do sometimes quit operating or get stuck. Another possibility is that you may have an air bubble in the system preventing the flow of the cooling system fluid.

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Heater is warm then stop and its cool

Age of the truck, probably clogged heater coil. Find where coolant runs in and out of firewall under hood. Try "backflushing" with a hose and collect the water as it comes out. You'll probably see sediment and lime build up from so many seasons. The water pump isn't pushing as hard so you might not be getting flow through the heater coil as much as when it's revving higher.

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No heat

There are several reasons for no heat. 1st, how is the temp gauge in the car? Is it in the normal range, or is it running cold or hot after warming up? How long does it take to warm up? 1st check the coolant level, make sure it is at the correct level, bleed system to remove any air (bleeder bolt usually located near the thermostat housing.) If that checks out ok, and the engine is not warming up, change the thermostat. If you still have a problem, the heater core may be plugged up with rust and sediment. Flushing the system may help to restore the flow of coolant to get the heat going again. Worst case scenario, system plugged beyond flushing out the crud, heater core would have to be replaced. Start with the easy stuff 1st, hopefully that will work. Good luck

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1 Answer

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I would flush the whole system with radiater flush then replace with new coolant. But make sure the heater is set to full heat when you flush it ( while driving around the block with flush in it) so the small radiater that has the hot water flowing through it gets flushed too. It may have some build up in it stopping the full flow of heated water/coolant through. If it is bad enough may need to remove and spray out the rubber hoses from the motor to the heater core, and possibly remove the heater core and hose it out to make it flow better and therefore increase the heating ability. Hope this helps.

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