Thermostat Wont Open?

[revivalroadfabworks]

At the start of this story, I had 2012 6.7, ATS twin-turbo kit, head studs, banks monster ram, deleted exhaust, EGR mounted but blocked off at the outlet, tuned.

About a month ago noticed my thermostat sticking in the morning or going home from work after the truck has 8+ hours to cool down (no heat in the cab either). The alarm would go off at 220, and I would pull over and shut it down. After a few minutes, I started it back up, and the thermostat opened, heat in the cab and coolant temp dropping to normal. Had this happened two times before I had an opportunity to swap in a new thermostat? Installed a Gates 192 degree thermostat from Geno's garage (my original 200 deg. thermostat was installed prior). I took a 2500 mile trip to Montana from California, pulling a 10k trailer during Christmas. Hence, it experienced warm and cold outside temps, worked perfectly, not one issue with the cooling system.

Fast forward a month, and I started experiencing the same thermostat sticking issue that I noticed before after 8hrs of sitting. I figured my aftermarket thermostat was garbage, so I picked up a POS NAPA brand thermostat to test out. The thermostat appeared to function fine, so I drove it home from my shop (10 miles). I parked for two days and had it stick again on the way to work. Hit 240, shut it down, heard the overflow bubble, started it up, thermostat opened, and I had heat in the cab again. Bled and bled and bled, I eventually noticed if I put a very slight amount of pressure on the radiator cap, I would hear bubbles passing by. I replaced the radiator cap with a POS Napa, experienced the same thing if I put some pressure on it (crappy fit). I ordered a factory cap from the dealership.

At this time, I removed my blocked-off EGR, installed block-off plates, and installed a Pusher Intake coolant riser reroute kit. Thoroughly drained the cooling system, used an Airlift vacuum radiator filling tool to test and fill. Vacuumed the cooling system for 20+ minutes holding 25 inches of vacuum. Used the Airlift to fill the system two times. I started it up, was still experiencing a thermostat that wouldn't open.

At this point, I purchased a no-spill funnel filler to install on the radiator neck to allow any air to escape. I performed three cycles of running the engine long enough to pop the thermostat. Shut it down, let it cool for 20+ minutes, remove the funnel, and install the new radiator cap. Let the truck sit for a few minutes while cleaning up, and noticed the coolant temp was stuck around 150-160, no heat in the cab again. I took it for a quick drive and saw fluctuating temps as the cooling system had an obvious air bubble.

I'm now at a loss—no sign of oil in the coolant or coolant in the oil.

I noticed no constant stream of tiny air bubbles as the engine came up to temp; I would only see bubbles after I ran the engine at 2k for about 45 seconds at a time and came to an idle.

I noticed my upper radiator hose is slightly saggy, so I would caress the hose and work air bubbles out into the funnel.

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[AK Bob]

The new thermostat, radiator cap, and vacuum/airlift fill are based on what you have already done.

I would do a coolant system combustion test to rule out the head gasket.


2014 RAM 3500 (Aisin) 3.73 4X4 Limited Crew Cab Long Bed DRW. Oil Bypass Filter, Fuel Filtration Kit, and 50 Gallon Aux Fuel Tank.

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[Badger2078]

Agree with AK Bob.

It sounds like an airlock against the thermostat if the issue is actually that the thermostat won't open.

Marine inboard engines with coolants use a thermostat with a small hole so air can pass and not overheat.

May temporarily bandaid by drilling a 1/8 hole in the thermostat plate?

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[revivalroadfabworks]

The new thermostat, radiator cap, and vacuum/airlift fill are based on what you have already done.

I would do a coolant system combustion test to rule out the head gasket.


2014 RAM 3500 (Aisin) 3.73 4X4 Limited Crew Cab Long Bed DRW. Oil Bypass Filter, Fuel Filtration Kit, and 50 Gallon Aux Fuel Tank.

The test kit is on order.

Agree with AK Bob.

It sounds like an airlock against the thermostat if the issue is actually that the thermostat won't open.

Marine inboard engines with coolants use a thermostat with a small hole so air can pass and not overheat.

May temporarily bandaid by drilling a 1/8 hole in the thermostat plate?

Sent from my SM-G973U using Tapatalk

Both my Gates and Napa thermostats have two holes in them each, with a bit of pins in each hole to seal the backside of the thermostat when there is pressure up against the pins.

I was thinking of snipping those off and testing in the meantime.

I am still thinking of running down to the Cummins dealer tomorrow to grab a legit Cummins branded thermostat to swap in as well.

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[Chrisn162001]

Test kit is on order.

Both my Gates and Napa thermostats have two holes in them each, with the little pins in each hole to seal the backside of the thermostat when there is pressure up against the pins.

I was thinking of snipping those off and testing in the meantime.

Still thinking of running down to the Cummins dealer tomorrow to grab a legit Cummins branded thermostat to swap in as well.

It’s doubtful you got three bad thermostats.

The Cummins oem does have a noticeable bigger spring on it vs. every aftermarket I’ve seen, but the aftermarkets have worked fine In my experience.

Since you vacuum filled it, assuming it’s done right leaves no change for air in the system.

It sucks, but it sounds like you have a head gasket issue.

What head studs do you have.

I would use 625s with compounds.

I have seen many heads lift with the 2000s and compounds utilizing a factory VGT, more so on the early 6.7s with the none pressurized coolant bottle.


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[revivalroadfabworks]

It’s doubtful you got three bad thermostats.

The Cummins oem does have a noticeable bigger spring on it vs. every aftermarket I’ve seen, but the aftermarkets have worked fine In my experience.

Since you vacuum filled it, assuming it’s done right leaves no change for air in the system.

It sucks, but it sounds like you have a head gasket issue.

What head studs do you have.

I would use 625s with compounds.

I have seen many heads lift with the 2000s and compounds utilizing a factory VGT, more so on the early 6.7s with the none pressurized coolant bottle.

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Regarding the thermostats, I had thought it may have been fine.

The bad radiator cap sucking in air while the engine was cooling down overnight was almost definite.

Unfortunately, I tossed the factory thermostat, so I couldn't inspect it after issues started popping up.

Yes, the HG could be a possibility.

I have ARP 425's installed.

Turbo setup is the ATS Aurora 7500 over their stage 1 VGT turbo, both brand new when installed.

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[Badger2078]

Again agree with the headgasket likelihood.

Yup, probably snip the pins out and reinstall the spring down.

To allow air to flow by.

This might not help with heat but should allow water to continue to circulate by opening the thermostat unless you have a terrible gasket leak

If the thermostat won't open bc of an airlock.

There is not enough water in the head for cooling, and a boil could occur.

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[revivalroadfabworks]

Again agree with the headgasket likelihood.

Yup, probably snip the pins out and reinstall the spring down.

To allow air to flow by.

This might not help with heat but should allow water to circulate by opening the thermostat unless you have a terrible gasket leak.

If the thermostat won't open bc of an airlock.

There is not enough water in the head for cooling, and a boil could occur.

Sent from my SM-G973U using Tapatalk

I snipped the jiggle pins and filled the head with coolant before reinstalling the thermostat.

Filled the cooling system and started the engine with the funnel on the neck of the radiator.

Had medium-sized bubbles coming out, not constant but seemed too much to me.

Didn't see a constant small stream of bubbles.

I couldn't see any bubbles like this with the jiggle pins in place.

I had great heat inside the cab, got the coolant to 170 with the cap off, couldn't get it any hotter to pop the thermostat.

I ended up draining the system again to pull a vacuum on the cooling system with the engine block warm/hot.

It pulled 25 inches, and it built up 2 inches over a 30-minute time frame.

I started the engine and ran for about 2 minutes, and the vacuum only dropped to 26 inches.

Tomorrow, I will borrow a pressure tester to check for any apparent leaks externally.

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[revivalroadfabworks]

Today I pressure tested the cooling system cold, up to 18psi.

No pressure drop at all over 10 minutes of holding.

While the system was pressurized, I started looking for signs of leaks.

I Sat my work light down on the lifting hook and heard a noise as it slid down onto the coolant riser hose.

Found a small air leak where my hose connects to the machined adapter (Pusher Intake Coolant Reroute Kit).

I tightened this up and went along with my testing.

Side note, I was curious how this never showed signs of a coolant leak, both cold and hot prior, but curious if a possible venturi effect was happening due to the necking down of the coolant adapter.

I started the engine to heat, filled just about full with coolant, drained some to perform the chemical test.

No color change in the dye. Performed this with the engine cold, just starting to warm up, and warmed up to 120 degrees.

Performed the chemical test 4 times after running the engine at just an idle, snap throttle multiple times, holding 2k RPMs for 45 seconds, and back to idle.

I took it for a drive only got up to 150 after about 10 minutes of driving which should have brought it close to thermostat pop temp.

I brought it back to the shop and parked the nose about 1ft higher than the rear.

I heard the radiator cap slightly flowing some fluid but couldn't see a noticeable rise or fall in the overflow.

I am letting it cool down enough to burp the radiator cap and top off once more.

I am thinking about swapping my thermostat with the jiggle pins back in.

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[AK Bob]

Today, I pressure tested the cooling system cold, up to 18psi.

No pressure drop at all over 10 minutes of holding.

While the system was pressurized, I started looking for signs of leaks.

I Sat my work light down on the lifting hook and heard a noise as it slid down onto the coolant riser hose.

Found a small air leak where my hose connects to the machined adapter (Pusher Intake Coolant Reroute Kit).

I tightened this up and went along with my testing.

Side note, I was curious how this never showed signs of a coolant leak, both cold and hot prior, but curious if a possible venturi effect was happening due to the necking down of the coolant adapter.

I started the engine to heat, filled just about full with coolant, drained some to perform the chemical test.

No color change in the dye. Performed this with the engine cold, just starting to warm up, and warmed up to 120 degrees.

Performed the chemical test 4 times after running the engine at just an idle, snap throttle multiple times, holding 2k RPMs for 45 seconds, and back to idle.

I took it for a drive only got up to 150 after about 10 minutes of driving which should have brought it close to thermostat pop temp.

I brought it back to the shop and parked the nose about 1ft higher than the rear.

I heard the radiator cap slightly flowing some fluid but couldn't see a noticeable rise or fall in the overflow.

I am letting it cool down enough to burp the radiator cap and top off once more.

I am thinking about swapping my thermostat with the jiggle pins back in.

Good news on the combustion test.

Not sure if that small leak on the Pusher coolant reroute kit would cause your thermostat issue.

However, I agree to put a new stock thermostat in, vacuum fills the coolant system, and see what happens.

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