Is the tension on a 3800 motor serpentine belt adjustable

Hi and thanks for using 2CarPros.

The belt is not adjustable. Tension is supplied by the serpentine belt tensioner. Although you feel tension when you place the wrench on it, chances are it is bad if the belt is loose.

First, here is a link that discusses belt routing for your vehicle:

https://www.2carpros.com/diagrams/buick/park-avenue/1998

Next, here is a link that shows in general how to replace a belt tensioner:

https://www.2carpros.com/articles/how-a-serpentine-belt-tensioner-works

https://www.2carpros.com/articles/serpentine-belt-tensioner-replacement

Here is a link showing how a belt is replaced:

https://www.2carpros.com/articles/replace-serpentine-belt

Now, your vehicle is a bit more tricky to replace the belt than most because one of the engine mounts needs removed to take the belt off. I am going to supply the directions for replacing the belt which is specific to your vehicle. All pictures attached correlate with these directions. You will need a jack to stabilize the engine so you can remove the mount. Make sure to follow the directions and be careful.

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Belt Replacement:

1998 Buick Park Avenue V6-3.8L VIN K
Accessory Drive Belt Replacement
Vehicle Engine, Cooling and Exhaust Engine Drive Belts, Mounts, Brackets and Accessories Drive Belt Service and Repair Removal and Replacement Accessory Drive Belt Replacement
ACCESSORY DRIVE BELT REPLACEMENT
REMOVAL PROCEDURE
The accessory drive belt drives all engine mounted accessories. All driven accessories are rigidly mounted to the engine. Drive belt tension is maintained by a spring loaded belt tensioner. A belt squeak when the engine is started or stopped is normal and has no effect on belt durability. The drive belt tensioner can control belt tension over a broad range of belt lengths; however, there are limits to the tensioner's ability to compensate. Using the tensioner outside of its operating range can result in poor tension control and/or damage to the tensioner.

Important: Ensure that the wood block extends past the width of the oil pan in order to avoid damage.

See Picture 1

1. Use a jack with a block of wood on the jack under the oil pan in order to support the engine.
2. Remove the engine mount to engine mount bracket nuts.
3. Remove the engine mount bracket front upper and lower nuts.
4. Remove the engine mount bracket front upper and lower studs and spacer.

See Picture 2

5. Lower the engine as necessary and rotate the tensioner to remove the drive belt.

See Picture 3

6. Remove the drive belt.

INSTALLATION PROCEDURE

See Picture 4

1. Install the drive belt.

See Picture 5

2. Install the engine mount bracket front upper and lower studs and spacers.

Notice: Refer to Fastener Notice in Service Precautions.

See Picture 6

3. Install the engine mount bracket front upper and lower nuts.
Tighten the nuts to 78 Nm (58 ft. lbs.).
4. Install the engine mount to engine mount bracket nuts.
Tighten the nuts to 87 Nm (64 ft. lbs.).
5. Remove the floor jack.

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Let me know if this helps or if you have other questions.

Take care,
Joe

Not a problem. I'm glad it helped.

Let me know if you need anything or have other questions.

Take care,
Joe