Tech Q&A Part #6

Low Fuel – Not


Is there anything I can do to my ’07 NBS Chevy 6.6L 2500 so the fuel gauge does not show low fuel with 6 gallons remaining in tank? Also, when this happens, the range shows as zero?

Thank You,

Michael F.
Reading, PA


Hi Michael,

Fuel gauges have always been somewhat inaccurate. However, it’s best for GM or any automaker to err on the side of showing less fuel in the tank than what is actually there. It’s intense towing a heavy trailer with your “Low Fuel” warning light on, and still have 50 miles to go to the next fuel stop. Having some cushion in the fuel tank can ease the stress a bit.

That said, yes, the fuel gauge can be recalibrated a bit by adjusting the float in the fuel tank. The process involves draining the tank, dropping the tank, removing the sender package, adjusting the float, then reassemble/refill and check.

I recommend just factoring the extra 6 gallons into your fuel stop calculations – without cutting it too close. This’ll also give you a cushion when the truck might not be quite level. I’ve run a diesel out of fuel because I cut it too close and the truck was off-road in steep terrain. Not a fun time – without tools. Let us know if you decide to recal the fuel level sender.

Bun Warmers


I have a 2006 GMC Duramax/Allison 2500 Sierra. I would like to know if other owners have experienced any problem with their truck’s heated seats.

This seat heater problem began about a month ago. When I push the heated-seat switch once, it lights up then turns off. After playing around with it, it finally stayed on. The seat warms up fine. Just yesterday, the same thing would happen, and I would go over to the passenger side and push the switch. That side stayed on, so I went back to the driver’s side and it stayed on. This game went on all day. Then last night the interior dome light wouldn’t go on, and both side switches wouldn’t stay on. I’m not sure what to do? Do you have a suggestion? Thanks.

Hal Nonneman
Anchorage, AK



I’d bet the heated seats are important where you live. It seems the electrical connectors for the seat heaters, located beneath the seats and through the carpet, can become partially unplugged – creating an intermittent operation. In some cases, an individual wire can sometimes pull out of an electrical connector and cause the same symptoms.

This problem sometimes happens when “things” get pushed or crammed under the seat. So, have a look at the electrical connectors. If the problem is due to an electrical connector becoming partially unplugged, preventing a re-occurrence may be as simple as using zip-ties or tape to help secure the connection.

The dome light may be a separate issue. With colder temperatures here, the door switch may be sticking a bit, which could delay the activation of the interior courtesy lamps. Good luck.

Intelligent Oil Life Monitor

I recently acquired a 2011 Ford F250 pickup truck powered by their 6.7L diesel. Some questions remain unanswered even after reading the owner’s manual. For example, how does the Intelligent oil life monitor work? Is it effective? Or, do owners of current diesel pickups simply stick with, say, a six months or 5,000 miles oil change interval? Also, can you tell me what are pros and cons of passive and active regeneration for the diesel particulate filter?

Wayne Smith
Peoria, AZ



For the 2011 model year, Ford’s “Intelligent Oil-Life Monitor” tracked oil temperature, Diesel Particulate Filter regeneration, engine idle hours and vehicle mileage, then alerts the driver when it’s time to change the oil (5% remaining) based on an algorithm determined by Ford’s own engine and lubrication engineers. So, Ford’s oil life monitor’s recommendation is based on several factors, each of which can affect oil life – mileage being just one of them. Actual miles driven between oil changes can range anywhere between 3,000 & 10,000 miles depending on how the truck was used during those miles.

To maintain your powertrain warranty, always service your truck according to the schedule found in your owner’s manual and as indicated by the Oil-Life Monitor. Changing oil more often can’t hurt, but you’ll need to reset the monitor whenever you do. Your owner’s manual contains a detailed set of instructions for resetting the monitor.

Modern diesels operate much cleaner and produce far less soot when compared to diesels in the 1990s. Soot in the oil drove oil drain intervals in prior decades. Soot is an abrasive. With cleaner engines that produce less soot (which finds its way into the oil), oil drain intervals have increased. This is all a good thing.

Passive regeneration of the DPF (Diesel Particulate Filter) occurs whenever the truck is being driven in ways that push exhaust temperatures high enough for DPF regeneration. In general, this will occur whenever the truck is cruising at Interstate speeds or certainly while towing. Passive regeneration can’t happen while driving around town – for example, especially during the cooler winter months. The exhaust gases are just too cool.

Active regeneration is a process that the vehicle computer manages. In short, raw fuel is injected into the exhaust stream, which ignites and burns just upstream to the DPF. This raises DPF temperatures and allows any accumulated soot to oxidize. An active regeneration consumes fuel, so your fuel economy will decrease slightly during those times when an active regeneration is occurring.

First-Gen Duramax Losing Coolant

I sure hope you can help me. I have a 2001 2500 with a LB7 that I bought new. I don’t drive it much, so it has only accumulated about 150,000 miles since leaving the dealership nearly 15 years ago.

The engine is losing coolant out of the coolant surge tank overflow whenever I use the truck to pull my 5th wheel travel-trailer. I’ve been to three GM dealerships and spent close to $2000, but the problem remains. The water pump, coolant tank and pressure cap have all been replaced, the heads have been checked for combustion leaks into the cooling system and all check fine. The radiator has been removed and cleaned and both thermostats have been replaced. The engine runs approximately 190-195 degrees while pulling my trailer, so overheating has not been a problem.

I’m at a loss and the GM mechanics appear to be guessing at what the problem might be. Can any of your readers or someone in the diesel community point me in the right direction? Please help.

Wes Blount
Rexburg, ID


Hey Wes,

Building pressure in the LB7 cooling system is most often due to either a leaking head gasket or a leaking injector cup seal. Most water pump seal leaks are the result of excessive cooling system pressure, so I encourage owners to measure cooling system pressure before and after a water pump replacement. Though the coolant surge tank cap is supposed to vent at 15-psi, too many of them hold up to as high as 20-psi. Cooling system pressure should normally run in the high single digits. Excessive cooling system pressure wipes out the water pump seal well before its time.

Though it’s a job, I would pull the heads and have them leak-tested yet again. At the same time, I would also have all eight injector cups re-sealed – which I believe is your engine’s problem. Then, put everything back together using the very latest in GM head gaskets and new Torque-To-Yield (TTY) head bolts, using the latest bolt torque sequence. GM has updated the gasket design and bolt torque sequence a couple of times since the LB7 was first introduced.

The eight individual stainless-steel injector cups are the only design blemish on an otherwise superbly designed engine. The injector cups are “wet”, meaning they are exposed to coolant on one side. The small end of each cup is also exposed to the tremendous combustion pressures found in each cylinder. The cups are sealed by only a small dab of Loctite 272 sealant and the clamping force applied by one small bolt, which anchors both the cup and the injector. When installed correctly, the cup seal performs very well, but we hear of far too many cooling system pressure problems that occur soon after an injector replacement. I suspect the original 272 sealant on one or more cups was disturbed when the associated injector was removed, which eventually resulted in a cooling system overpressure problem. Resealing the cups whenever an injector is removed is the only way to help prevent a cup leak. Good luck. DW

If you like the Q&A series, here’s the previous post in the series: Tech Q&A Part #5

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