Coolant overflow/reservoir tank question

[liquify33]

I have a coolant leak / weep from the intake manifold and so I have to add coolant to the tank, but my rad stays full.

Might also want to get a new rad cap, it is supposed to be regularly replaced.

Hope that all helped some.

I’ll add it to the list. The mileage is low (115k) for a 99 and the previous owner only put 5k miles/yr on it. I’m going through gaskets and plastics that have been in the south for 20 years. The radiator and shroud appears to replacements, so a cap is probably wise though probably not original.
I did fill and check the radiator level and all is well level wise, with heater and engine temp. Gauge always reads at the first major tick mark.
This all started when I needed defroster heat and it wasn’t hot. The hose to the water heater seems kind of kinked, I waited a bit and opened the cap and oops. This whole time the reservoir level never budged.

 

[liquify33]

I’m gonna test this weekend with a new radiator cap, but sadly I’m leaning towards leaking intake manifold gaskets.

I can smell hot coolant after a long drive and I’ve got a continuous leak under the center of the truck.
Water pump area is dry as a bone but I noticed while changing oil last weekend there was coolant on steering components and the transmission dipstick.
My next checks are:
Cap
Radiator
Intake gaskets

 

[HiHoeSilver]

I’m gonna test this weekend with a new radiator cap, but sadly I’m leaning towards leaking intake manifold gaskets.

I can smell hot coolant after a long drive and I’ve got a continuous leak under the center of the truck.
Water pump area is dry as a bone but I noticed while changing oil last weekend there was coolant on steering components and the transmission dipstick.
My next checks are:
Cap
Radiator
Intake gaskets

You're probably right. Intake gaskets are common on the gmt400s. I know I had to do mine once.

 

[OR VietVet]

I would guess intake leak as well because you are smelling not only hot coolant but what is getting on exhaust and then drips down.

 

[liquify33]

I would guess intake leak as well because you are smelling not only hot coolant but what is getting on exhaust and then drips down.

Update: filled while running and replaced the cap and the smell is gone.
I added some distilled water to the reservoir and let it run another 10 mins, did see some small bubbles while it ran.
Dry as a bone underneath for now.

ETA: it’s running about a needle width cooler on the gauge. 165Tstat I believe.

 

[OR VietVet]

Update: filled while running and replaced the cap and the smell is gone.
I added some distilled water to the reservoir and let it run another 10 mins, did see some small bubbles while it ran.
Dry as a bone underneath for now.

ETA: it’s running about a needle width cooler on the gauge. 165Tstat I believe.

What is your fuel mileage? That stat is not the factory recommendation temp. Should be a 195-198 degree stat. I can only assume you changed to that degree stat trying to help run cooler if was running hot.

 

[liquify33]

What is your fuel mileage? That stat is not the factory recommendation temp. Should be a 195-198 degree stat. I can only assume you changed to that degree stat trying to help run cooler if was running hot.

12.5-13.5 mostly stop and go in Houston (thus the 165), up to high 15’s on a highway tank at 80.
I changed t-stat with the water pump in Feb/March.

ETA: Do you think I should go back to 195/198?

 

[OR VietVet]

Many of the engine heat sensitive sensors are typically dependent on the engine temp with the correct temp stat. The newer the rig the more sensitive that can be and that can effect your fuel mileage in a closed loop oxygen sensor system.

 

[liquify33]

Update again:
I replaced t-stat with a 195, took the reservoir off and cleared the tube. It was plugged up.
Ran it up to temp, still shows at first major tick mark on the gauge, will keep an eye on the tank and see if she moves.
There was a good sized puddle under the truck passenger side so I may still have to replace the intake manifold gaskets. My driveway has a decent angle and this was after a short trip and mostly parked all day.
I’ve got to do plugs/wires and replace the AC compressor and drier so I may just wait for a good weekend to really tear it up.
2 questions:
1) does anyone have a part number for the heater hose disconnect on the manifold? I’ve heard they are prone to breaking
2) can I pull the throttle body and see if it has the spider upgrade? Seems like it would be much easier with the intake off the truck if I had to do it. Or should I just leave it alone (runs great).

 

[exp500]

Take a look around the heater control valve. That plastic may have a pinhole. Wrap some TP around it, if it gets wet it shows. Also check at Heater hose QD at intake manifold.