triumph stag oil and filter service guide

How to Change Your Triumph Stag's Oil and Filter: Complete Service Guide

Estimated reading time: 10 minutes

Key Takeaways:

  • Change your Stag's oil every 6,000 miles or annually using 5 litres of 20W-50 oil
  • The V8 engine requires oil with ZDDP additives to protect flat-tappet camshafts
  • Always replace the copper drain plug washer and filter housing seal
  • Warm oil drains more effectively and carries more contaminants
  • Milky oil indicates coolant contamination requiring immediate investigation
  • Fresh oil before winter storage protects against corrosion during layup

Keeping your Triumph Stag's iconic 3.0-litre V8 engine running smoothly starts with regular oil and filter changes. As straightforward as this task might seem, some specific requirements and techniques can make the difference between a well-maintained engine and one that develops problems down the line.

Whether you're a hands-on enthusiast or simply want to understand what your mechanic should be doing, this guide walks you through everything you need to know about servicing your Stag's lubrication system.

Why Regular Oil Changes Matter for Your Triumph Stag

The Triumph Stag V8 engine has earned itself an undeserved reputation for unreliability over the years. In truth, many issues stem from neglected maintenance rather than fundamental design flaws.

Fresh oil is your engine's lifeblood, performing several critical functions simultaneously. It lubricates moving parts, reduces friction and wear, carries away heat from critical components, and suspends contaminants until they're trapped by the filter.

The Stag's aluminium cylinder heads paired with a cast iron block create different thermal expansion rates. This makes proper lubrication even more important.

Old, degraded oil loses its ability to protect these surfaces, leading to increased wear on camshafts, tappets, and bearing surfaces.

The result can be expensive repairs that were entirely preventable with regular servicing.

Think of it this way: a £30 oil change every 6,000 miles is considerably cheaper than a £3,000 engine rebuild.

Understanding Your Stag's Oil Requirements

Oil Capacity and Specification

Your Triumph Stag's engine requires approximately 5 litres of oil when performing a complete oil and filter change. The sump itself holds 4.5 litres (1 gallon), whilst the oil filter adds another 0.5 litres (1 pint). When you're ready to service your Stag, make sure you have at least a 5-litre container on hand.

The recommended oil grade for the Stag V8 is 20W-50 multigrade oil with at least an API SF rating. Modern classic car oils that meet this specification work brilliantly. Many Stag owners have excellent results with oils specifically formulated for classic vehicles, which contain the appropriate levels of ZDDP (zinc dialkyldithiophosphate) that flat-tappet engines like the Stag require.

This anti-scuff additive is essential for protecting the camshaft and tappets from premature wear. You'll find suitable engine oils for your Triumph Stag at Rimmer Bros, where we stock a range of oils specifically chosen for classic Triumph engines.

Service Intervals: When to Change Your Oil

The official recommendation is to change your Stag's oil and filter every 6,000 miles or annually, whichever comes first. However, many experienced Stag owners prefer a more conservative approach, especially if the car sees limited use or only short journeys where the engine doesn't reach full operating temperature.

Regular Use: For cars used regularly with a mix of driving conditions, 6,000 miles is perfectly acceptable with quality oil.

Limited Mileage: If your Stag covers just a few hundred miles per year, consider changing the oil annually regardless of mileage. Oil degrades over time even when sitting idle, and moisture can accumulate in the crankcase during storage.

Short Journeys: Short trips where the engine doesn't fully warm up can be particularly harsh on oil. Water vapour and combustion byproducts don't fully evaporate, leading to oil contamination and the formation of sludge.

If this describes your driving pattern, consider more frequent changes every 3,000 miles or every six months.

Step-by-Step: Changing Your Triumph Stag's Engine Oil

Gathering Your Tools and Materials

Before you begin, assemble everything you'll need. Having the right tools to hand makes the job far more pleasant and reduces the risk of mistakes.

Essential Items:

  • 5 litres of 20W-50 engine oil (minimum API SF rating)
  • New oil filter (standard or spin-on type, depending on your setup)
  • New sump drain plug washer
  • Oil filter housing seal (if using cartridge-type filter)
  • Container for old oil (at least 6-litre capacity)
  • Socket set including 13mm for the drain plug
  • Oil filter removal tool or strap wrench
  • Jack and axle stands
  • Wheel chocks
  • Funnel
  • Clean rags
  • Disposable gloves

Consider picking up one of our Triumph Stag engine service kits, which includes the essential filters and seals you'll need for a complete service.

Preparing Your Stag

Warm the engine to operating temperature by running it for about 10 minutes. Warm oil flows more freely and carries more contaminants with it when drained. Don't let it get too hot though – you still need to work underneath the car safely.

Park on level ground and apply the handbrake. Place wheel chocks behind the rear wheels for extra security. Raise the front of the car using a jack and support it securely on axle stands. Never work under a car supported only by a jack.

Draining the Old Oil

Position your drain container beneath the sump drain plug. The plug is located at the rear of the sump and requires a 13mm socket. Before loosening it completely, have your drain container ready and positioned to catch the oil flow.

Remove the drain plug fully and allow the oil to drain completely. This takes several minutes – be patient and let gravity do its work. The oil will emerge with some force initially, so position your container accordingly.

While the oil drains, remove the oil filler cap from the top of the engine. This allows air in and helps the oil drain more thoroughly. Inspect the drain plug and washer. The copper washer should be replaced every time – these are inexpensive items that ensure a proper seal. You'll find sealing washers readily available.

Replacing the Oil Filter

Your Stag came originally with a cartridge-type oil filter housed in a metal canister on the side of the engine block. Many owners have converted to spin-on filters, which are simpler to change. The procedure differs depending on which type you have.

For Cartridge-Type Filters:

Unscrew the central bolt holding the filter body to the engine block using a socket. Remove the filter body carefully – it will contain old oil. Extract the old filter element and clean the inside of the housing thoroughly.

Inspect the rubber seal on the filter body and replace it if it shows any signs of deterioration or cracking. Insert the new filter element, ensuring it sits properly in the housing. Refit the filter body with a new rubber seal, ensuring the sealing faces are clean. Tighten the central bolt to 26-32 lb-ft (3.6-4.4 kg.m).

For Spin-On Filters:

If you've fitted a spin-on oil filter conversion, the process is much simpler. Use an oil filter removal tool to unscrew the old filter. Some oil will spill, so keep rags handy.

Before fitting the new filter, apply a thin film of clean engine oil to the rubber seal. This ensures a good seal and makes the next removal easier. Screw the filter on by hand until the seal makes contact with the mounting face, then tighten it a further three-quarters of a turn. Don't overtighten – hand-tight plus three-quarters turn is sufficient.

You can source the correct oil filter for your Stag from Rimmer Bros with confidence in getting the right specification for your engine.

Refilling with Fresh Oil

With a new washer fitted, refit the sump drain plug and tighten to 16-20 lb-ft. Don't overtighten – you're threading into aluminium and it's surprisingly easy to strip the threads if you're too enthusiastic.

Lower the car from the axle stands and remove the jack. Place your funnel in the oil filler opening and pour in approximately 4.5 litres of fresh oil. Replace the oil filler cap and start the engine. Let it run for about 30 seconds, then switch it off.

Wait a few minutes for the oil to settle into the sump. Check the dipstick level. The oil should be between the minimum and maximum marks. Top up as necessary to bring it to the correct level. It's normal to need the full 5 litres when you account for what stays in the filter and various oil passages.

With the engine running, check beneath the car for any signs of leakage around the drain plug or filter. Also, check that the oil pressure warning light extinguishes promptly. If it remains illuminated, switch off immediately and investigate.

Professional Tips for Stag Owners

Breaking In a Fresh Engine

If you've just had your engine rebuilt or are running it for the first time after significant work, use a mineral-based running-in oil for the first 500 miles. This allows the piston rings to bed in properly. Avoid fully synthetic oils during this period, as they can be too slippery and prevent proper ring seating.

After the running-in period, change to your chosen 20W-50 oil and perform the first oil change after just 500 miles to remove any initial wear particles. After this, revert to the standard service intervals.

Checking for Issues

Your used oil can tell you a lot about your engine's condition:

  • Very dark, thick oil suggests you've left it too long between changes
  • Milky appearance indicates coolant contamination – possibly from a head gasket issue that needs addressing
  • Metallic particles or glittery appearance can indicate bearing wear

If you notice any of these warning signs, investigate further rather than simply changing the oil. The Stag's reputation for head gasket problems means you should be particularly vigilant about signs of coolant contamination.

Oil Cooler Considerations

Many Stag owners fit aftermarket oil coolers to help manage engine temperatures. If your car has an oil cooler fitted, you'll need to account for the additional oil capacity in the cooling system. Typically, this adds another litre to your oil capacity requirements.

Browse our selection of Triumph Stag oil cooler kits if you're considering this worthwhile upgrade for your engine's longevity.

Environmental Responsibility

Dispose of your used oil properly. Never pour it down drains or onto the ground. Most local recycling centres accept waste oil free of charge, or you can take it to a garage that will recycle it on your behalf. The same applies to oil filters, which should be drained thoroughly before disposal.

Keep used oil in a sealed container away from children and pets. It's toxic and presents environmental hazards if not handled correctly.

Next Steps: Keeping Your Stag in Top Condition

Regular oil changes form the foundation of Stag engine maintenance, but they're just one part of keeping your V8 healthy. Consider the following as part of your routine care:

  • Check and maintain the correct coolant strength
  • Inspect timing chains and tensioners
  • Monitor valve clearances
  • Keep the carburettors properly tuned
  • Ensure the cooling system is working efficiently

For comprehensive service information and parts availability, explore our complete Triumph Stag vehicle information pages, where you'll find detailed specifications and guidance for all aspects of Stag ownership.

Your Triumph Stag represents a unique piece of British automotive history. With proper care and attention to maintenance, particularly regular oil changes with the correct specification oil, these engines can cover impressive mileages and provide years of reliable service. The key is being proactive rather than reactive with your servicing schedule.

Get Everything You Need from Rimmer Bros

At Rimmer Bros, we stock everything you need to service your Triumph Stag properly. From filters and oils to complete service kits and specialist tools, we're here to support Stag owners with expert advice and genuine quality parts. Visit our Triumph Stag parts section to browse our full range.

Need advice or want to order parts? Call our team on 01522 568000 – we're always happy to help fellow Triumph enthusiasts keep their cars on the road. Whether you're tackling a service yourself or need to order parts for your mechanic, we can ensure you get exactly what your Stag needs.

Remember, proper maintenance today prevents expensive repairs tomorrow. Your Stag deserves the best care you can give it – and that starts with regular, quality oil changes.

Common Questions About Triumph Stag Oil Changes

Can I use modern, fully synthetic oil in my Stag?

You can, but choose carefully. Modern fully synthetic oils formulated for current vehicles often lack the ZDDP content that flat-tappet engines need. Look for oils specifically designed for classic vehicles or those marketed for older engines. Some owners report excellent results with synthetic oils that meet the right specifications, whilst others prefer traditional mineral oils.

How do I know if my oil filter housing seal needs replacing?

If you notice oil seeping from around the oil filter housing, the seal needs attention. These rubber seals harden and perish over time. As a general rule, replace the seal every other oil change, or more frequently if you notice any weeping. They're inexpensive insurance against messy oil leaks.

My oil pressure seems lower than it used to be. What should I check?

Several factors affect oil pressure. First, check you're using the correct grade – 20W-50. Thinner oils will give lower pressure readings. Worn bearings can also reduce pressure, as can a weak pressure relief valve. If pressure remains acceptable when cold but drops when hot, this often indicates bearing wear. Have this investigated promptly to avoid serious engine damage.

Should I change my oil before storing my Stag for winter?

Absolutely. Old oil contains acids and contaminants that can corrode internal components during storage. Change the oil and filter before putting your Stag away, then take it for a short drive to circulate the fresh oil throughout the engine. This gives you the best protection during the storage period.