Dealing with Your own LLY Thermostat Issues
Replacing out an lly thermostat isn't exactly how I'd select to spend a Saturday afternoon, but if your Duramax is starting in order to run hot or—even worse—won't warm-up with all, it's one of those jobs you simply can't ignore. The particular 2004. 5 in order to 2005 LLY motors are legendary for a lot of reasons, but their cooling systems are high on the list of points owners love to grumble about.
If you've invested any time on the truck forums, you know the LLY includes a bit of a reputation for excessive heating, especially when you're pulling a large trailer up a grade. While generally there are a couple of aspects that play in to that, the thermostats are often the first line of defense. If they stop performing their job, things go south quite quickly.
Why the LLY Makes use of Two Thermostats
It might seem such as overkill, but the LLY actually uses a dual thermostat setup. You've got one sitting in the front and one within the rear associated with the housing. They aren't identical either, which is some thing that trips the lot of individuals up when they're ordering parts intended for the first period. Usually, one is fixed to open at 180 degrees F and the additional kicks in with 185.
The idea behind this is to have got a staged cooling response. The first opens up to obtain some flow heading, as well as the second a single provides that extra burst of cooling capacity when the particular engine really begins working hard. It's a smart style on paper, but it means you have 2 points of failing instead of 1. If the 180-degree stat gets trapped, you might notice your gauge hovering the little higher than usual. If the 185-degree one neglects to open, you're looking at a significant overheat situation the next time you hit the particular highway.
Understanding When Yours Are usually Shot
Sometimes it's obvious when an lly thermostat has bit the particular dust, but other times it's a gradual crawl toward failing. The most irritating scenario is whenever they get trapped open. You'll become driving later on in the middle of winter, and your heater feels like it's blowing lukewarm surroundings at best. Your engine temperature measure might never actually reach the quarter mark. Not only does this make the cab gloomy, but it also hurts your gasoline economy since the motor never leaves "warm-up" mode.
Upon the flip aspect, getting stuck shut is the scary version. You're cruising along, and instantly that needle begins climbing toward the particular red. If you call at your temps spiking and then suddenly falling, that's a traditional sign of the thermostat that's "hunting" or even sticking before lastly snapping open.
I've furthermore seen cases exactly where the rubber seal off on the thermostat itself starts in order to disintegrate. When that happens, little bits of rubber can really avoid the valve from seating properly. It's a mess, and it's usually a sign that the coolant hasn't been flushed in way too long.
Selecting Your Replacements
When it comes to buying fresh ones, you've generally got two paths: OEM AC Delco or something like a Mishimoto high-flow set. Most of the time, I'd tell you to stick with OE. The AC Delco stats are constructed for this engine and they generally be very durable. However, mainly because the LLY is definitely so prone in order to heat issues, the lot of men swear by the lower-temperature thermostats.
You can find sets that open at 174 degrees instead of the factory 180/185. The logic is the fact that by getting the coolant moving previously, you have more of a "buffer" before the engine gets dangerously hot. If you live in a place like Az or spend your summers towing the 5th wheel by means of the mountains, the particular lower-temp lly thermostat might actually be a solid update. But if you're up in the north where this hits sub-zero temperature, you will probably find that your truck takes permanently to get the particular cabin warm in the morning.
Tips for the Installation
In fact changing them out there isn't the toughest job in the particular world, but this is of a "skinny-arm" task. The thermostat housing sits right at the very best front of the particular engine, but there's a lot of stuff in the way. You'll likely find yourself leaning over the grille for a hr, so a fender cover or a good old blanket is really a must unless you want your belt buckle to scratch the paint.
One thing you totally have to watch out there for is the bolts. These issues have been heat-cycled thousands of periods, and so they love to seize up. I usually hit associated with some penetrating oil the night before I plan in order to do the work. If you breeze one of those bolts away from within the lower casing, you're going to have a quite bad day regarding drill bits plus extractors.
When you pull the particular old ones out there, take a 2nd to look at the alignment. You need to make certain the new ones go in precisely the same method. Also, don't be tempted to reuse the old mechanical seals. Most new lly thermostat sets come with the silicone seals, but double-check that before you start. There's nothing worse than getting it all buttoned up only to notice a steady drip-drip-drip on the front yard.
The Air Pocket Headache
The largest "gotcha" with the LLY air conditioning system is air pockets. After a person replace the thermostats and top away from the coolant, a person aren't done. These engines are well known for trapping air flow in the heating unit core or the upper part associated with the block.
If a person just fill this up and drive away, you might see the temp gauge spike almost instantly because there's a big bubble associated with air sitting perfect at the lly thermostat casing, preventing the statistics from sensing the specific water temperature.
The trick is by using the bleeder screw on best of the thermostat housing. You'll want to crack that open up while the motor is running (and after it's arrived at operating temp) to allow air hiss out. Just end up being careful—that coolant is hot, and it'll spray. I use a long electric screwdriver and stay back again a bit. As soon as you obtain a constant stream of water with no pockets, you're usually good to go. It's also the smart move in order to keep a gallon of 50/50 mix in the vehicle for the next couple of days, as the level within the flood tank will most likely drop as the final few bubbles function their way out there.
While You're inside
Considering that you're already messing with the cooling program, it's a great time to take a look at the rest of the "stack. " The LLY has a tightly packed group associated with coolers—the radiator, the intercooler, the AIR CONDITIONING UNIT condenser, and the particular oil cooler are usually all sandwiched collectively. Over time, dirt, leaves, and "road grime" get trapped together.
In case your new lly thermostat doesn't seem to be fixing your own high temps, it's probably because your own radiator is clogged with junk. I like to get a garden hose (not the pressure washer, you'll bend the fins! ) and spray out the stack from the back side. You'd be surprised at the amount of mud that comes out of a vehicle that looks clean externally.
Final Thoughts
It's easy to forget about the thermostats until they will cause a problem, but on an LLY, they're quite much a servicing item. If you've got over 100k miles on your current set, or if you've just bought an used truck and don't know the history, it's cheap insurance in order to just swap all of them out.
It's one of those fairly inexpensive fixes that can save a person from a multi-thousand-dollar head gasket job straight down the road. Simply take your time, don't force the mounting bolts, and make sure a person bleed the environment out properly. Your Duramax will definitely thank you for it the following time you're tugging a heavy load up a steep hill.