2006 duramax 6.6 coolant seeps pass the over flow while driving but not while parked

Not real familiar with your engine, but generally you have two coolant temp sensors. One just runs the dash gauge. the other speaks to the computer and acts sort of like a choke. If the computer thinks the engine temp is hotter or cooler than it actually is, fuel metering will be wrong. The more likely culprit is the low fuel pressure. I have even seen a bad fuel cap cause something like this, as these systems operate under pressure I believe.

you may have 1 of 2 things it may be a seeping head gasket allowing coolant to seep into cylinder overnight or it may be valve seals leaking allowing oil to seep by valve seals onto valve smell the smoke as coolant will have a sweet smell and if its oil thats what it will smell like

have a coolant pressure test done to check for leaks. Have a flow test done on the radiator to check for blocked cores. Have a compression test done to check for head gasket and cracks.

have a compression test done to check for head gasket and cracked head.. Have a coolant system pressure test done to check for cooling system problems. have a flow test done to check for blocked cores. Check that the fans are working correctly. Check condition of fins on radiator as flaking fins will not transfer heat.

I am told the glow plugs heat up in "firing" order, also the Duramax uses a intake air heater to warm the air on cold starts.

Park the Nissan Altima on a flat surface and set the parking brake. Next, open the hood and check the external temperature of the radiator. If the radiator is warm to the touch, wait for the radiator to cool before you continue.

Twist the radiator cap one turn to relieve any pressure. Step back from the radiator and allow a few seconds to pass, and then completely remove the radiator cap.

Place a bucket or tray with at least a 2-gallon capacity underneath the radiator and below the drain plug. The drain plug on a Nissan Altima is on the passenger side bottom of the radiator.

Loosen the drain plug and let the old coolant drain completely into the bucket. Take care while loosening the drain plug, because it's plastic and can be brittle. Pour the old coolant into a sealable container for proper disposal later and put the bucket back under the drain plug opening.

Close the drain plug and pour distilled water into the radiator until it's full. Then, open the drain plug and let the water flow into the bucket. Keep repeating this procedure until the water runs clear and debris free into the bucket. You will need at least 3 gallons of distilled water.

Make sure to tighten the drain plug and fill the radiator with fresh coolant. Refill the radiator to within an inch of it overflowing. Check the drain plug and hoses for any possible leaks.

Start the Nissan Altima and turn the heater to the high setting. Let it run for about 10 minutes and shut the engine off. Check the coolant level and refill, if necessary. Finally, put the radiator cap on and close the hood.

Any smoke coming from your tailpipe? Could be a blown head gasket and is allowing coolant to seep from your jackets(passages) to your combustion chambers. How about strange odor in your exhaust? Does your fan kick on when at normal operating temperature? How quickly does it use coolant?

Remove or disconnect the following:

Air outlet duct Coolant Inlet radiator hose from the water pump Upper fan shroud Cooling fan and clutch assembly Drive belt Radiator outlet hose from the coolant pump Surge tank hose Heater hose Water pump



DO NOT use cooling system seal tabs (or similar compounds) unless otherwise instructed. The use of cooling system seal tabs (or similar compounds) may restrict coolant flow through the passages of the cooling system or the engine components. Restricted coolant flow may cause engine overheating and/or damage to the cooling system or the engine components/assembly.
Install or connect the following:

Water pump. Install the water pump bolts. Tighten the water pump bolts first pass to 11 ft. lbs. (15 Nm); tighten the bolts final pass to 22 ft. lbs. (30 Nm). Water pump drive belt pulley and bolts (if applicable). Tighten the pulley bolts first pass to 89 inch lbs. (10 Nm); tighten the bolts final pass to 18 ft. lbs. (25 Nm). Surge tank hose Heater hose Outlet radiator hose to the coolant pump Drive belt Cooling fan and clutch assembly Upper fan shroud Inlet radiator hose to the water pump Air inlet duct Coolant

the maximum pay load is 3534 lbs (3.5 tons ) and the maximum towing capacity is 18000 lbs or 9 tons
from your description of 2 thermostats I take it is a v8 hopefully a 6.6 ltr v8 turbo diesel
it should have come with a 6 speed allison auto transmission.
with a 35ft, 5th wheeler behind it the combined gross max mass would be getting close to max allowed
add any speed on the highway and the transmission will be running at high oil temperatures and that heat is transferred to the radiator by the transmission oil cooler in a tank of the radiator
the high oil temps could be slippage in bands and clutch packs in the transmission( not noticeable under normal driving conditions) so an check and adjustment would not go astray
next if the adjustments are set properly, it may become necessary for you to consider an air to air transmission cooler so that the heat from the transmission is transferred to passing air flow and not accumulated and added to engine coolant temperature
those kits are available from most accredited transmission specialist shops and will reduce the transmission oil temp by at least 40%
taking that the coolant temp is 95 -98 c the transmission oil will be running a lot lower, saves the oil and the transmission and will help prevent boiling of the coolant
it may be necessary for you to lock up the fan clutch as well

check coolant....sounds like its low....seep or small leak....could be water pump or hose seeping...good luck...Lee