Engine temps lower than normal and no heat in cab

[MolonLabe420]

Hey guys. Something fishy is going on with my cooling system. All of a sudden I'm not getting any heat thru my vents unless I'm driving and under load. Normally I would be worried about the truck overheating while I'm sitting in traffic if the hot coolant isn't flowing all the way thru the system properly, but when Im idling the heat stops blowing in the cab and the temp gauge starts going down. Then when I can give it a decent amount of throttle the heat will come back and the gauge goes up to 186ish.
I thought I had a sticky thermostat so I swap them both out and the same problem remains... the low coolant alarm is on the dash but it's not actually low. I used the bleeder multiple times now after driving and letting it cool down. Its right on the mark.
Also, as soon as I shut the engine down I hear some gurgling somewhere for a few seconds. I assume that is air in the system but I've bled it properly.... what am I missing?
What are your thoughts?
Thanks

 

[Dkatubi06]

Seems like there’s still air in the system, how does your upper radiator hose feel after driving for a while?rock hard after sitting overnight and It may be a head gasket issue, soft I would rule that out. Where about a in pa are ya located?

 

[TheBac]

Clean or replace the overflow cap. Cheap and easy to try first...

 

[MolonLabe420]

Thanks for the tips. I checked the cap and it looked pretty clean. I dryed it off and put it back on... might get a new one anyways. The upper rad hose is soft while the truck is cold, not sure about hot.
I also replaced the radiator about 3 months about. Its been fine until now.
Could a bad water pump cause this?

 

[MolonLabe420]

I'm from Berks County, PA. We get pretty rough winters here, usually.

 

[clrussell]

Have you put thermostats in the truck?

 

[ironmax]

Yes he did

Sent from my SM-J337A using Tapatalk

 

[ironmax]

Just a question but would a stuck clutch fan keep the motor from heating up? I know its engaged when cold to speed up engine getting to temp but at what point would it or could it work in reverse. as in, keeping the motor from fully warming up?

OP, try pitting some cardboard in front of the radiator and see what happens.


Sent from my SM-J337A using Tapatalk

 

[DAVe3283]

If your thermostats are working, even if the fan sticks on, it will heat up. I never run a radiator cover in the winter; it gets down to 10-15°F (-12°C or so) and I have heat even at high speeds with 80 MPH ram air through the radiator. All a stuck on fan hurts is your fuel mileage.

Every time I have had a lack of heat it was from failed thermostats. Even brand new ones can fail in a couple months if you're unlucky. Hard to find quality parts sometimes. I'd swap them out with new ones again and see what happens.

 

[2004LB7]

Could these symptoms happen if the thermostats where put in backwards or should I say, the front put in the back and back in the front? Would it make bleeding the air out more difficult?

 

[Dkatubi06]

A bad water pump and it would leak, and get too hot and over heat. Also might have a clogged heater core. If you were a little closer to me I’d swing through and take a peek at the situation I’m outside of philly.

Another thing to consider is a bad head gasket or injector cup. Does your truck have an EGR cooler on it? If so I’d look into that. Only a Cali emmisions equipped Lb7 would have one

 

[N2BRK]

Don't know how far south and east, but if you aren't far from Cherry Hill you can stop over and we can bleed it with a vacuum fill and be sure of no bubbles, but prior to having that neat little toy I've never had air issues with just using the bleed screw by the thermostats.

Are you sure that you did the t-stat swap correctly?

 

[Dkatubi06]

He’s about an hour away from me and your about 45 minutes from depending on our good old pa/nj traffic so he’s about two hours from you

When I did my lly swap I had air issues and only drove 20 minutes to work and damn near blew the upper rad hose off. I wouldn’t want to him chance it

 

[MolonLabe420]

Ok so I did put new thermostats in and they are definitely installed correct.. I double triple checked everything twice!
I am a man of incredibly shitty luck, so if those thermostats are brand new trash it wouldn't even surprise me. I just don't have an extra $50 right now to beat a dead horse...
Someone said that the heater core might be clogged.... I can believe that from the way it's acting. How can I try to unclog it??
If that's the case, is the engine circulating coolant properly and staying at the right temp? My fear is that something is blocking the sensor from getting an accurate temp reading and the engine is actually overheating while the gauge is telling me it's getting colder.... is that possible?
As for the temp gauge going down while not under a heavy load, how is the sensor getting that reading? Could the sensor be bad and throwing something off?
Yesterday I let it warm up for about 30min and it only got up to 174°. When I started to drive, the temp went down to 147° then it slowly went up to 202° and then ran a steady 181°. I had heat pretty much right away, until I lifted off the throttle.
I'm not leaking anything and don't seem to be burning anything other than diesel....
The EGR is deleted.
I don't have proof or confirmation but when the truck was on a lift, it looked like the head gaskets were brand new clean.
As for the air bubbles, what's the best way to clear them out?? Someone said to park on a hill facing up and then park facing down to try to move them around.
Also, how do I figure out if the clutch fan is working properly?
Sorry so long, any advice is much appreciated!

 

[2004LB7]

I bleed mine just with the bleed screw on top of the thermostat housing. Nothing special, just on a level surface. With the engine idling crack the screw open a few turns until you see air bubbles. Leave it until it runs clear. Make sure you dont let the reservoir run dry

Not complicated at all.

 

[LBZ]

Sounds to me like you are getting exhaust gasses in the cooling system with how much that temp is swinging around. I’d get a test kit and check for exhaust gasses in the cooling system to rule that out.

 

[duramax on fire]

Fan clutch will sound like a school bus or 18 wheeler fan when it kicks in almost.

Heater cores can get clogged sometimes and get an air bubble that can't push threw. Happened to me on the coldest day of the year on a system that hadn't been touched in 10 years. To check heater core for sufficient flow feel the two hoses going into it at the fire wall. If ones hot the other cold with heater off you know it's clogged or got air. Usually I remove the two hoses and flush water threw it.

 

[Dkatubi06]

So here’s my suggestion,
Go purchase or rent or barrow what we in the auto field call an AIR lift tool.

You’ll need an air compressor with at least a ten gallon capacity. A CLEAN 5 gallon bucket

Drain your coolant out from the bottom of the radiator into said clean bucket.

The tool itself you will attach onto the degas bottle. You’ll need to pinch off the overflow hose as well or put a bolt in the end and hose clamp it. Put the radiator drain plug back in and tighten

This is a very straight forward process. The less coolant in the system the better.

You’ll need to hook your airline into the valve and turn it on.

What this tool does is sucks all positive air from the cooling system and puts it into a vacuum. Most of us will suck the system down to 25. And let it stay there. If the needle doesn’t move there’s NO leaks. If it moves air is getting in somewhere.

To refill there’s a hose that will come with the tool it goes into the bucket of coolant also have more on hand if there was an air pocket more coolant will be need to fill the space.

It’s a very good way to test

I has served me well in the past and has also un-clogged a few heater cores in some cases

There are plent of you tube videos on this particular process