1958-1959 GMC 150 Engine Oil Pressure Switch: A Comprehensive Guide
Understanding the signs of a failing oil pressure switch is key to protecting your classic GMC's engine.
- A bad oil pressure switch can give false readings; always check your oil level first to rule out a real engine problem.
- Common signs of failure are a constant or flickering oil light, a gauge that reads zero or max, or oil leaking from the switch itself.
- For this vintage truck, a new aftermarket part from a reputable brand like Standard Ignition is the best and most practical replacement option.
- Replacement is a simple DIY task for most owners, requiring basic tools and less than an hour of time.
Is Your Oil Light or Gauge Acting Up?
A faulty engine oil pressure switch can cause a lot of worry. It might give a false warning of low oil pressure, or worse, fail to warn you when there's a real problem. Since the engines in the 1958-1959 GMC 150, whether it's the GMC inline-six or the Pontiac-based V8, rely on steady oil pressure, a working switch is essential. Before assuming the worst, it's important to know the signs of a bad switch versus actual low oil pressure.
Symptoms of a Failing Oil Pressure Switch
If you notice any of these signs, the oil pressure switch is the likely culprit, but you should always check your oil level immediately to be safe.
- Oil Light Stays On or Flickers: The most common symptom is an oil pressure warning light on your dash that flickers or stays on, especially if you've confirmed the oil level is correct.
- Gauge Reads Zero or Maxed Out: If your truck has a pressure gauge, a bad sending unit can cause the needle to stay at zero or shoot to its maximum reading, even with the engine off.
- Erratic Gauge Readings: The gauge needle may jump around randomly, not corresponding to engine speed or load. This is a tell-tale sign of a failing sender.
- Visible Oil Leak: The switch itself can fail and leak oil. If you see oil seeping from the sensor body or its electrical connector, it needs to be replaced.
Important: Rule Out a Real Problem First
An oil pressure warning can signal a serious mechanical issue. Always turn off the engine and check the dipstick. If the oil level is low, top it off. If the light or gauge still shows a problem after confirming the oil level is good, the switch is the next logical part to inspect and replace.
Choosing the Right Aftermarket Part
For a vehicle from the late 1950s, finding new original equipment (OEM) parts is nearly impossible. New Old Stock (NOS) parts are rare and expensive. The most practical and common solution is a new aftermarket part.
Standard Ignition: A Reliable Choice
Standard Motor Products (the parent brand of Standard Ignition) has been making aftermarket components since 1919 and is a well-regarded name in the industry. Their oil pressure switches are manufactured to meet original specifications and undergo testing to ensure they provide accurate readings. For a simple, crucial part like an oil pressure switch on a vintage truck, a Standard Ignition replacement is a dependable and affordable option.
Estimated Costs for Replacement
| Part Type | Cost Range | Notes |
|---|---|---|
| New Aftermarket (Standard Ignition) | $16.58 | The most common and recommended option. |
| New OEM | Not Available | No longer produced by the original manufacturer. |
| Shop Labor | $60 - $120 | Typically a shop's minimum charge (0.5-1.0 hours). |
Pro Tip: Installation
Replacing the switch is usually a simple DIY job. It's typically located on the engine block, often near the oil filter or distributor. The process involves disconnecting the single wire, using a wrench or a special socket to unscrew the old unit, and installing the new one. Applying a small amount of thread sealant to the new switch's threads is recommended to prevent leaks.
Frequently Asked Questions (FAQ)
Will a bad oil pressure switch cause my truck to run poorly?
No. On a 1958-1959 GMC 150, the oil pressure switch is just for the warning light or gauge. It does not send information to any computer that controls the engine, so a bad switch will not affect engine performance. Modern vehicles can be different.
Are there any recalls for the oil pressure switch on my truck?
Searches of the National Highway Traffic Safety Administration (NHTSA) database and other records show no recalls or technical service bulletins (TSBs) for the oil pressure switch on the 1958-1959 GMC 150. This is normal for a vehicle of this age.
My truck doesn't have an oil light, it has a gauge. Is it the same part?
No, the parts are different. A switch for a warning light is a simple on/off device. A part for a gauge is called a "sending unit" or "sender" and sends a variable signal. While they perform the same basic function of monitoring pressure, you must order the correct part for your truck's specific dashboard setup (light or gauge).
Do I need a special tool to replace the switch?
Sometimes. Many switches can be removed with a standard deep-well socket or wrench. However, some have a unique shape that requires a special oil pressure switch socket for easier removal without damaging the part. It's best to inspect the old switch first to see what tool will be needed.
Technical Specifications
The specific part will vary depending on whether the truck is equipped with a warning light (switch) or a pressure gauge (sender).
We Have This Part in Stock
The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.