Low coolant light and no heat related?

[GTackett]

Our 98 montana "low coolant" light has been coming off and on for a few months (even though there has always been plenty of coolant in the radiator and the reservoir). In the last week the heat has only been "hot" while controls are in the heat position only intermittently.

There is plenty of air flow. I haven't had a chance to check the temp. of the hoses to the heater core to see if they are hot, my guess is they are because when the heat does come on it comes on instantly and it is very warm.

The thermostat is operating properly as the temp. guage rises steadily and maintains 180 +/- operating temp.

I believe the Air Mix Door Actuator may be the problem, but I wonder if the "low coolant" light may have something to do with this problem.

Doe anyone know if the "low coolant" light and the Air Mix door (possible) problem could be releated?

Thanks,
Greg

[LMP]

UNless I"m thinking of some other car, I think the low coolant sensor is located in the overflow tank which level when cold should be at about 1/3. Can you verify if this level is actually lower than that? OR do you have to replenish this tank often? THis alarm in itself is completely independant of the mixer door, but the heat problem may be related to the level alarm.
As I understand, occasionally, you have no heat from the heater...., which could be a mixer door problem, or a problem related with the "low level" alarm....
FOr the time being, verify or maintain the overflow tank level where it should be and come back here with any other symptoms, like occasional bursts of spraying coolant or steam ...

[GTackett]

As I stated in my post, both the radiator and overflow reservoir levels are fine, nevertheless the "low coolant" light comes on intermittently.

I did notice the radiator cap had something black and gummy on it. I replaced the cap. Is this the Dextrol coolant breaking down?

[LMP]

Yeah indeed you had stated the condition of the overflow tank. Maybe the sensor is simply screwed up. THis leaves your suggestion about the mixer door as a legitimate option .Checking that first will tell if you can stop there.

[Hoags]

GTackett, I left you a thread response on the Montana Forum. it sounds like the mixer door is a seperate issue from the low coolant sensor. Like LMP states, the sensor should be at the overflow tank, It may be faulty or just dirty from the old coolant, I have seen them get dirty and have cleaned them off and replaced and they work fine. If you found crap on the cap make sure you get the coolant systen flushed to get rid of all of the dirty fluid you don's want to compromise the new coolant it will not work to full potential.

[GTackett]

It appears the "low coolant" light was connected to the no heat problem.

Common problem with this engine, but a different side effect: lower intake gasket.

Either the low coolant sensor was dirty from oil contaminating it, or the coolant was low due to some being sucked into the intake.

An air pocket was being created in the coolant system (due to leaking intake gasket) which was giving me intermittent heat problems.

[mmmantei]

My 98 transport has been doing the same thing. The "low coolent" light, the intermittent Heat, no heat, oops got heat again. I have not noticed any smoke out the tail pipe, so I do not suspect a coolent leak into the engine. If it is indeed an air pocket in the cooling system would I be able to simply bleed it out by running the engine with the radiator cap off?

Mike

[LMP]

An air pocket in the system does not develop by itself from nowhere, and anyway would be a temporary situation that would clear by itself by natural means if overflow tank level is maintained; so if you have not had any work done on car like changing coolant pump, flushing coolant and replenish, changing radiator, then the air is taken from somewhere else. Head gasket failure is common and does not give unescapable signs from exhaust pipe - after all water is a natural by product of combustion and there is already plenty of water that goes out the exhaust pipe. In fact, more than 3 quarts of water are exhausted as vapour (except when exhaust pipe is cold, then it condenses) each time you burn 1 gallon of fuel - so a few drops of coolant do not change much.

One other now frequent failure is the intake gasket - now because use of dissimilar materials like cast iron and aluminum is rather recent and aluminum has 3 times the expansion rate of cast iron, so gaskets are constantly rubbed on from both sides - . Intake manifold is most of the time under a vacuum when the engine functions and this vacuum is able to siphon water by a tiny leak that would have developped, and then air enters the cooling system very easily by the radiator cap (that has a one way valve TOWARDS the cooling side that opens at almost 0 pressure differential) as soon as overflow tank is empty. SInce this leak is exploited by vacuum, then at rest, coolant will not invade the combustion chambers, so no sign in oil. IN fact, IF leak develops also to the atmosphere side, some coolant that may leak to the manifold at rest will leak and be seen on and outside of engine. And since exhaust has no access to the intake manifold and to that leak, there are no exhaust bubbles from the radiator.
In fact, one key question here: do you have to add coolant from time to time????? It seems you do since the "low level light" comes on.....so coolant is going somewhere......and air is replacing it.

[mmmantei]

I have owned the Van since April of 04 and have never needed to replenish the coolant. The light did not start coiming on until maybe mid November, and I have kept a watchfull eye on it since then. How much of a chore is replacing the gasket? I work under the hood quite a bit, but there is no room under this hood to do anyhing! As long as I have someone listening, do I have to take the exhaust manifold off to get to the thermostat housing? Any help is greatly appreciated.

[LMP]

OK...that woud exclude the intake manifold gasket as a cause.....! THere has been a lot said in the "timguili" thread that you probably have seen....
I do not have photos of the 3.4 but just as the other blocks, thermostat is normally easy to get at, and there should be a plug on the thermostat housing that can be revoved to vent air from the system.
Changing head gasketS is an awful job given the position of the engine but is listed as an "on vehicle service"......I've never done it on this vehicle so others should come and list their own perception of the job. Exhaust crossover pipe, exhaust manifolds must be removed , the a/c compressor too, etc....not a very "user friendly environment......
I have the detailed instructions for the 3.1 and 3.8 and they are much alike and are surely a very close indication of same steps with the 3.4
If need be, I'll scan them for you unless someone comes with the exact story for the 3.4