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2008 buick lacrosse heat problems

upstateny

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2008 buick lacrosse
I bought it 2 years ago with 38k miles and the heat worked fine. The temp gauge never quite got up to the center point where it should be reading. It always stuck around 40%-ish. But the heat worked fine so I never looked into it.

Fast forward to these past couple weeks. The heater wasn't blowing hot air, just mild warm. Cool enough to be an issue in upstate NY in the winter. So I took it in to valvoline for a flush.[It needed one anyway] After the flush now it's blowing out COLD air. They reflushed it for free after I took it back the second time. Still ice cold.

Now I go back a third time to have their more experienced tech look at it. He immediately noticed the 2 big fans right behind the radiator aren't running while the car is on and 'up to temp' with the heat on full blast. He told me I'd have to take it to a real mechanic or fix it myself if I was able.

It seems a few things could cause this. I'm betting it's a defective sensor or switch. What do you guys think?

  • Defective temperature switch, coolant sensor or other sensor
  • Engine thermostat is stuck OPEN (engine never gets hot enough to turn on the fan)
  • Faulty fan relay
  • A wiring problem (blown fuse, loose or corroded connector, shorts, opens, etc.)
  • Bad fan motor
  • Defective fan control module
 
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2007LucerneCXL

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Check both heater core hoses after the car is up to operating temperature, they should feel about the same amount of heat as the upper radiator hose. If not both are about the same then it may be a inside HVAC acuator is the problem. If one hose is warm and the other cold then the core is plugged and may need a good flushing. These are probably the quickest test without getting into all the other items until needed. Hopefully the shop burped the system properly as air in the heater core can create a similar problem.

Not really sure how to trust a quicklube grease monkey on vehicle dianogist.
 

upstateny

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2008 buick lacrosse
Check both heater core hoses after the car is up to operating temperature, they should feel about the same amount of heat as the upper radiator hose. If not both are about the same then it may be a inside HVAC acuator is the problem. If one hose is warm and the other cold then the core is plugged and may need a good flushing. These are probably the quickest test without getting into all the other items until needed. Hopefully the shop burped the system properly as air in the heater core can create a similar problem.

Not really sure how to trust a quicklube grease monkey on vehicle dianogist.
The top one is hot and the bottom one is cool. So, clogged heating core then?
 

2007LucerneCXL

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Certainly points as the problem, having the coolant system changed it may have loosen up some material and clogged the heater core. Just connecting the dots on what events have been described as nothing else seems to be a problem with the rest of the system. If the thermostat hasn't been done that should be probably on the list as most items are at a 100k or 10 years maximum usage, it's age and/or milage.
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upstateny

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Alright, cool. Shouldn't be too difficult or expensive to fix. I figure I can probably do it myself based off of the few youtube videos I've seen so far.

I think the tech wasn't too sure what the hell he was doing. He opened up the coolant while the car was hot....without a rag. O_O I'm not sure if it blasted him in the face or what but he ran off for a minute and came back with a rag to open it up the rest of the way. Anyway, like you said, I'm not sure if he can be trusted with what he said regarding the fan. Its freezing up here and the lube shop isn't far from my house. So for all I know[and hope!] the car just wasn't hot enough to trigger the coolant fans into turning on.

Anyway, you wouldn't happen to know where the thermostat is and how difficult it is to get to would you? A push in the right direction would be much appreciated.

Thanks for all your help
 

Regal LTD Coupe

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I personally wouldn't be bringing my car to those sorts of places for anything and if I ever did I'd be supervising every move of theirs. They probably never did a proper flush of the heater core; they might have done just the coolant through the regular evacuation drain at the bottom of the radiator probably if anything causing an already clogged heater core to get worse when refilling the system. The heater core needs to be backflushed by removal of the lines going into the firewall and through those ports. I wouldn't worry about the fans not coming on unless the car starts overheating or something; the computer tells them when to come on.
 

upstateny

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They sucked out the old fluid from the front opening port with a vacuum machine that had 3-4 tall cylinders. It wasn't a power flush, more of a simple drain and fill. I figured they knocked old shit particles loose and that clogged it. I watched him the whole time.

It was close by and their price wasn't bad. Plus they did it twice for the price of one. So there's that. *shrugs*
 

2007LucerneCXL

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3.8L series has the thermostat right on top, just follow the upper radiator hose to the housing. Get a top line thermostat and you will need to drain coolant out. Couple videos on the net or use the Chilton manual.

Here's a free Chilton manual on the forum, scroll down to post #19 for new login link and password.
Free Chilton Online Repair Manual
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upstateny

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Alright so,

I didnt have access to a garden hose or an air compressor so I figured I'd just blow the line the old fashioned way.

In my haste I accidentally did it the wrong way - I blew into the intake[hot/top] instead of the output [bottom/cold] line. I imagine doing it this way was a hell of a lot harder. It took a few tries but I finally got it to shoot out into my collection jug.

It looked filthy brown. I held the line up and filled up the core with cool water and blew it out twice more. I then filled it with 50/50 mix and reconnected the hoses.

I started up the car and hit the gas. Gurgling sounds. I figured it must be air pockets. I took off the fill port cap and hit the gas a few times. Recapped. No more gurgling.

I drove it and got it up to temperature. Good heat coming out. Drove it some more. Now its SUPER hot. HELL YEAH!

The gauge is still reading a bit wonky. It stays pretty steady at 40%-ish but shoots up to 45 and almost 50% intermittently. It could be gunk still in the line or maybe just a bad thermometer.either way, the heat problem is fixed!

Thanks for all your help guys :)

Pic attached of the coolant temp readout after being fully heated up.
 

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mark bark

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That filthy brown stuff is dex kill and corroded aluminium and your wonky temperature gauge is telling you your radiator is nearly clogged. My experience has been that flushing and backflushing the radiator won't work, but new ones are $50 on e-bay and changing the radiator isn't a hard job. There are plastic lines running to the heater hose connections that will crack when the engine overheats. It's a good idea to replace them with aluminium lines.
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upstateny

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2008 buick lacrosse
That filthy brown stuff is dex kill and corroded aluminium and your wonky temperature gauge is telling you your radiator is nearly clogged. My experience has been that flushing and backflushing the radiator won't work, but new ones are $50 on e-bay and changing the radiator isn't a hard job. There are plastic lines running to the heater hose connections that will crack when the engine overheats. It's a good idea to replace them with aluminium lines.
Could it just be an faulty thermometer? I dont see how the therm reading could indicate a clogged radiator.

As someone else said the thermometer should be replaced after 100k/10yr anyway so maybe I'll start there. If it ends up overheating I can always swap out the radiator. 🤷‍♂️
 

oldschool

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In reference to your temp gauge, that's where mine runs in the summer while towing my boat.
The rest of the year it normally sits half way between 1/4 and 1/2 or slightly less than yours.
 
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mark bark

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That's your choice. I've have never had to change fan thermostat or electronic temperature sending unit. My Lacrosse used to warmup quickly. With a new radiator it takes just as long to warm up as the century does. However once the sludge built up in my cooling system the engine has always ran warm no matter how many times I've backflushed and flushed the block. Your temperature indicator matches mine, so its running warm with a light load.
 
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