For the 1981 Buick Regal with the 5.7L 8-cylinder Diesel engine (Engine Code N), the oil capacity is 7 quarts (including filter replacement). Recommended viscosities include 10W-30 for temperatures below 16°C, 15W-40 for -18°C to 16°C, and 30 weight for continuous driving above 0°C. AMSOIL recommends using Signature Series 10W-30 Max-Duty Diesel Oil paired with an AMSOIL Oil Filter (EAO64-EA).
What oil does a 1981 Buick Regal 5.7L Diesel take?
The 1981 Buick Regal 5.7L Diesel requires an oil grade of CF. The specific viscosity depends on your operating temperature: use 10W-30 for temperatures below 16°C, 15W-40 for between -18°C and 16°C, or a 30 weight oil for continuous driving above 0°C.
AMSOIL product recommendations
The following AMSOIL products are specifically listed for your 1981 Buick Regal 5.7L Diesel to assist with routine maintenance and engine protection.
Engine Oil & Filter Kits
| Product Name | Code |
|---|---|
| Signature Series Max-Duty Synthetic Diesel Oil 5W-30 & Filter | DHDQT-EA |
| Signature Series Max-Duty Synthetic Diesel Oil 10W-30 & Filter | DTTQT-EA |
| Heavy-Duty Synthetic Diesel Oil 10W-30 & Filter | ADNQT-EA |
Component Specific Fluids & Filters
| Component | AMSOIL Product | Code |
|---|---|---|
| Engine Oil | Signature Series 10W-30 | DTTQT-EA |
| Engine Oil | Signature Series 5W-30 | DHDQT-EA |
| Engine Oil | Heavy-Duty 10W-30 | ADNQT-EA |
| Oil Filter | AMSOIL Oil Filter | EAO64-EA |
| Coolant | Passenger Car & Light Truck Antifreeze | ANTPC1G-EA |
| Coolant | Propylene Glycol Antifreeze | ANT1G-EA |
| Transmission | Signature Series Fuel-Efficient ATF | ATLPK-EA |
| Transmission | OE Fuel-Efficient ATF | OTLQT-EA |
Engine Oil Specifications
| Viscosity | Temperature Range |
|---|---|
| 10W-30 | Below 16°C |
| 15W-40 | -18 to 16°C |
| 30 | Above 0°C (Preferred for continuous driving) |
Oil Grade: CF
Engine Oil Capacity & Torque
| Detail | Specification |
|---|---|
| Capacity (with filter) | 7 quarts |
| Oil Drain Plug Torque | 30 ft/lbs |
Note: Always check the oil level after refilling.
How much transmission fluid does it take?
Transmission capacity varies by the specific model of the automatic transmission installed in your vehicle. For the THM350, the total fill is 10 quarts with a 3-quart initial fill. The THM250C requires a 10.8 quart total fill with a 4-quart initial fill.
Automatic Transmission Specifications
| Transmission Model | Total Fill Capacity | Initial Fill |
|---|---|---|
| THM350 | 10 quarts | 3 quarts |
| THM350C | 10 quarts | 3 quarts |
| THM250C | 10.8 quarts | 4 quarts |
| THM200C | 9.4 quarts | 3.5 quarts |
Note: The manufacturer’s Technical Service Bulletin indicates that the specification for these transmissions has been updated from Dexron II or III to Dexron VI.
Cooling System Maintenance
The cooling system capacity for this vehicle is 17.4 quarts. Maintaining proper coolant levels and quality is vital for preventing overheating in these older diesel architectures.
| Component | Capacity |
|---|---|
| Coolant System | 17.4 quarts |
Diesel maintenance notes for this vehicle
- Oil Filter Efficiency: The AMSOIL Oil Filter (EAO64-EA) provides 99 percent filtering efficiency at 20 microns and is designed to offer greater capacity for small, wear-causing contaminants.
- Air Filter: No recommendations available from the source data.
- Oil Vapor Filter: No recommendations available from the source data.
Common diesel oil-related concerns and how AMSOIL products may help
| Concern | Why it matters | AMSOIL Product | How it may help | Limitation |
|---|---|---|---|---|
| Engine Wear | Diesel engines face high pressure and friction. | Signature Series 10W-30 | Delivers up to 6X more wear protection. | Requires proper maintenance intervals. |
| Extreme Temperatures | Viscosity changes can affect lubrication. | Signature Series 5W-30 | Excels in extreme temperatures. | Not a substitute for mechanical repair. |
| Contaminants | Small particles can cause engine damage. | AMSOIL Oil Filter | 99% efficiency at 20 microns. | Must be replaced according to service schedule. |
Recall, TSB, and manufacturer communication notes
NHTSA recall research for the 1981 Buick Regal identified three specific campaigns:
Disclaimer: Always verify open recalls by checking your specific VIN through official manufacturer or NHTSA channels.
About this vehicle
The 1981 Buick Regal represents a specific era in General Motors’ history when the company attempted to capture a significant portion of the American light diesel market. As a mid-size car, the Regal was positioned as a premium intermediate vehicle within the Buick lineup.
This particular model is equipped with the 5.7L (350 cu in) V8 diesel engine, which belongs to a family of diesel engines produced by General Motors between 1978 and 1985. These engines were architecturally based on the Oldsmobile 350 gasoline engine design. While sales for these GM diesel engines peaked in 1981—accounting for a large majority of the U.S. passenger diesel market at the time—the V8 variant is historically noted for significant reliability challenges.
From a maintenance perspective, owners should prioritize rigorous maintenance schedules, particularly regarding cooling systems, fuel delivery, and timing components, as these were common areas of concern for the V8 architecture compared to later designs. Because specific technical details regarding ‘Engine Code N’ are not explicitly detailed in all research snippets, owners should verify exact engine specifications through a service manual or VIN decoding before performing major mechanical work.
Common questions about this vehicle’s diesel oil and maintenance
What is the oil capacity for my 1981 Buick Regal 5.7L Diesel?
The capacity is 7 quarts when replacing the filter. Always check your oil level after refilling.
Which AMSOIL oil is best for extreme temperatures in this engine?
AMSOIL Signature Series Max-Duty Diesel Oils (such as DTTQT-EA) are designed to excel in extreme temperatures and maintain proper viscosity.
What should I use for the automatic transmission?
The lookup notes that specifications have been updated from Dexron II or III to Dexron VI. AMSOIL offers Signature Series (ATLPK-EA) and OE Fuel-Efficient (OTLQT-EA) synthetic fluids.
How often should I change my coolant?
While specific intervals aren’t listed, AMSOIL products like the Propylene Glycol Antifreeze provide protection for up to 150,000 miles or 5 years in passenger cars/light trucks.
Is there a torque spec for my oil drain plug?
Yes, the oil drain plug should be torqued to 30 ft/lbs.
How can I verify if my vehicle has an open recall?
You should always use your VIN to check for active recalls through the NHTSA or your local Buick dealer to ensure safety components like wheels or suspension bolts are addressed.
Disclaimer: Information provided is based on available source data. Always consult your original factory service manual or a verified parts catalog before performing maintenance.