ujm

We've owned our Maxima for years, and it never ever put out heat in any quantity or quality.

I did not want to mess with the thermostat, that seemed to be the culprit, I kept blowing it off.

Long story short, the vacuum hoses on the heater control valve. I just cut a small amount off the end of each one, now there is more heat than is needed

GRNMAXDMON

iTrader: (1)

Good find. Glad you figured it out. I had the same issue a few years back.

ujm

It's a lie, a total bald faced lie -

I drove the car to KC today, it was 14 degree's out, the heater does not work on the highway, the temperature gauge stayed buried on burrrrrrrr

In town, it would warm up. Add some cardboard in front of the radiator, helped a minute amount, I still think it's the thermostat.....

chrome91

iTrader: (1)

thermostats probably stuck open

ac max 92

iTrader: (13)

It's worth changing the thermostat being that it's inexpensive and you can also get a higher temp. thermostat their is 2 options one being 88 deg. and the other 95 deg. i believe dont quote me on the degrees part but i know there is 2 options one hotter than the other.

oldpuck81

The water valve remains open until the solenoid valve closes the vacuum valve which thusly closes the little butterfly valve inside your heater line. The heater control valve aka water c*ck control, functions to turn OFF the flow of hot water when you move the temp switch all the way to cold (left). It then engages what is called the Full Cold Switch that shuts the water valve.
So, you had high hopes, followed by false gratification, followed by intense frustration. Join the club!!

Here are some possible problems/solutions:
a. Your heater core is clogged enough that you're not getting enough coolant except when you rev it up. Solution: power flush the heater core, or, (gasp) remove/replace the heater core. (See my thread on the heater core job ad nauseum.)

b. You have an air bubble in your heater core (possibly due to a partially clogged core). Burp the cooling system. Raise front end up 30"+ and run the motor until you see all the bubbles burping out of the radiator. This will take up to 1/2 hour. Find a nice steep little hill or a really high floor jack.

c. Your thermostat is not working properly. Doubtful. When stats go bad, they either don't close all the way or open all the way. If they don't open all the way, your engine might overheat but you might not have enough cabin heat. If that's happening, your cooling fans would be running a lot. If the stat is stuck open, eventually you'll get heat after the motor is pulling load at normal rpm's. Doubtful. Stats have a big spring that causes them to fail closed. I think a stat would have to be pretty old and crusty to not operate properly. But I could be wrong! I've changed mine in both the 90 & 94 GXE and it didn't make much difference. You can take it out and test in a pot of boiling water and it should open up.

d. Your water pump is failing and not circulating enough coolant. Doubtful. The fins on the pump impeller would have to be worn off before this happens and if it is bad, you'd probably have a bad bearing in it, too, and there'd be a puddle of coolant under the car at night.

My bet is you have a bad air bubble that's not clearing because you have a hi percentage of clogged passages in the core and it's not allowing the air to escape thereby only giving you about 50% heating if that much. Also, your cooling system is gunked up and it needs a power flush. But if you power flush it, you'll probably further clog up the heater core. Or probably not. I think I'd take the chance and power flush it with some good coolant system cleaner.

My 94 GXE exhibited all of these conditions. My 90 GXE was almost as bad but it never needed a heater core replacement. When my 94 was under 120k miles, it blew hot air like Wash. D.C. The past 3 years, it gurgled and wouldn't heat up until I ran the crap out of it. When I burped it, it was better, but since it had a pin-hole leak in the core, eventually the system sucked air back in and developed the air bubble in a couple of days. When I finally figured everything out and saw the puddle of coolant in the passenger floorboard, I realized my fate.

At this point (if you're still awake!) a heater core job is about 1/2 the cost of the current value of these cars--if you've been doing all the necessary maintenance! It's basically 2+/- months of car payments if you were to go out and buy a new car. Since I'm a DIY car whisperer, I'm doing the full frontal assault on the problem myself.
Good luck!

chrome91

iTrader: (1)

not always, my Hardbody was giving decent heat but not enough. thermostat was partially stuck open from age, replaced it and got cooking hot heat. had the same thing in my Silverado, thermostat was stuck only partially open from age

oldpuck81

yeah, if his temp gauge is too low, then it would be a stuck open stat. But these old Maximas have evil heater problems. I've been through all of them and now I'm fixing the "Big One"- the heater core- after I've fixed everything else on it.

ujm

Temp gauge does not move when it is really cold and there is air movement through the radiator. Warms up around town - get out on the road, burrrrrrrrrrrrrrrrrrr

I've replaced the coolant twice since I've owned it, both times it looked great.

Due to the recent accident and "repairs on the cheap" it might be a good time for this Maxima to go away, but, it's been in our family for a long time -

Tough decision......

oldpuck81

Sounds like the stat is bad. Replace it and water pump while you're down there. A good power flush and then burp the heater and you should be good to go. Be careful when pulling off hoses from the heater core tubes and the firewall heater valve- they are plastic and get weak w/ age.
Old Maximas are great cars when they're maintained, total frustration when they're not...but then, isn't any car?

ujm

Earlier this week I sold the Porsche 944 that I bought in 1998 - That car was a total PIA PLUS the parts are outrageously priced, even when discounted.

I'll do my best to never, ever buy anything "German Engineered" again, especially after my run-in with SAP......

oldpuck81

ha ha!! yeah, they're great when they're new!! That's why we kicked their a$$e$ in WWII cuz they tried to make their machines too good instead of just making a boat load of 'em. But when they worked, they were awesome.
I loved the look of the 944 when it came out. Dallas had a lot 'em running around in the 80's. I really liked the 928- that was my favorite big Porsche.

Grumpy560

iTrader: (1)

^^Is why I am moving on from a W126 S class 560. Though I have to admit it has been the easiest "German Engineered" car I have ever worked on in the past 8 years I've owned it but nothing compared to insanely hard to find and over priced parts for a Porsche period!

I don't plan on selling my 560, just moving onto something else for a change and hopefully the 1990 GXE digidash I bought from another forum member last week will be a perfect replacement project, I just wish it was here right now instead of Iowa.

lukky13

Interesting. Thank you for posting this find. I'm curious to know how this helped exactly.

I'm having similar heater problems and have been replacing nearly all possible culprits within the last year. I might try this, but i also want to learn, which is why i ask.

DennisMik

iTrader: (2)

The valve to let hot engine water into the heater core is operated by vacuum, so if the vacuum hose has become brittle due to age, it no longer seals tightly and allows air to leak in.

I had this problem on my 94 and a new piece of hose worked wonders.

Hectic

iTrader: (20)

My thermostat has been thermosticking for years now. Even seems to have gotten better year to year with more constant heat. Obviously needs replacing, but ain't got no time fo dat.

Technically you don't even have to drain the system though, so it's a simple job, no good reason to put it off..

Max_5gen

iTrader: (2)

When I had my 3rd gen I replaced that valve altogether- it has rubber inner coating which separated from the wall and got stuck across its pipe preventing water from passing through. The valve has 2 different modifications which are not interchangeable, please make sure you're buying the correct one, they look very similar but don't fit.
Another problem with my car was radiator cap- its built in valve lost seal preventing pressure from building up in the system and coolant- to reach its operating temperature. After I replaced it with OEM all hell broke lose in terms of coolant leaks . Telling sign for this problem- significant variations of the coolant level in the expansion tank, it's supposed to be fairly stable as the valve is supposed to be mostly closed.
My thermostat also got stuck open and it was the easiest thing to fix out of them all.
The last problem was air locks in the system- unless you can find that bleeding screw with your eyes closed you haven't been freezing in your Maxima yet
It started to put out heat after I took care of all of the above, so there's light and hope