Mishimoto MMHOSE-GM-15U Upper Radiator Hose for 1967–1969 Pontiac Firebird

Pontiac 350 versus Chevrolet 350

The listed 350ci application refers to the Pontiac-built 350 V8, not a Chevrolet small-block 350. Despite identical displacement numbers, the engines have different coolant outlets, accessory layouts and hose requirements.

This hose should not be assumed to fit:

• Chevrolet small-block swaps
• Chevrolet big-block swaps
• LS engine conversions
• Pontiac inline-six engines
• Custom radiators with relocated inlets
• Modified thermostat or water-neck configurations

Classic cars tend to collect engine swaps and creative repairs over six decades. Verify the hardware, not the story attached to the car.

Five-Layer Silicone Construction

The MMHOSE-GM-15U uses five layers of silicone reinforced with heat-resistant fibers. This construction provides improved tolerance for engine heat, cooling-system pressure and long-term deterioration.

Features include:

• Five-layer silicone construction
• Heat-resistant embedded fibers
• Maximum temperature rating of 330°F
• 1.50-inch inside diameter
• 1.89-inch outside diameter
• Molded factory-style shape
• Black finish
• Two worm-gear clamps
• Mishimoto Lifetime Warranty

What’s Included?

The package contains:

• One black silicone upper radiator hose
• Two worm-gear hose clamps

This is an upper hose only. Mishimoto sells the corresponding lower radiator hose separately.

Factory-Style Fit for Classic Firebirds

The hose is molded to connect a compatible Pontiac V8 thermostat housing to a factory-position radiator inlet. It can also work with many direct-fit aluminum radiators that retain the original inlet location and diameter.

Measure before ordering if the Firebird has:

• An aftermarket aluminum radiator
• A replacement water neck
• A non-original Pontiac engine
• A Chevrolet engine conversion
• A serpentine accessory conversion
• Custom radiator mounting
• A relocated radiator inlet

When Should a Firebird Radiator Hose Be Replaced?

Replace the upper hose if you find:

• Cracks around either connection
• Soft or swollen areas
• Coolant stains near a clamp
• Hardened rubber that no longer flexes
• Abrasion from an accessory or fan shroud
• Oil contamination
• Steam or coolant spray
• Repeated coolant loss
• Engine overheating

Use our guide on how to find a coolant leak if the source is not immediately visible. Small leaks may appear only after the cooling system builds pressure.

Installation Overview

Never remove a radiator cap from a hot engine. Allow the cooling system to cool completely.

A typical installation involves:

1. Confirm the engine and radiator configuration.
2. Drain enough coolant to lower the level beneath the upper hose.
3. Remove the existing hose clamps.
4. Carefully separate the old hose from both connections.
5. Inspect the radiator inlet and thermostat housing for damage.
6. Clean corrosion and old hose material from the sealing surfaces.
7. Compare the new hose with the original.
8. Install the hose without twisting or stretching it.
9. Position both clamps behind the raised fitting beads.
10. Refill with coolant suitable for the engine and radiator materials.
11. Bleed trapped air from the system.
12. Bring the engine to operating temperature.
13. Inspect both connections for leakage.
14. Recheck the coolant level after the engine cools.

The commonly published Mishimoto worm-clamp specification is approximately 22 in-lb, with an operating range around 18–27 in-lb. Confirm the current instructions supplied with the hose before tightening.

Use our cooling-system flush guide if the coolant is rusty, contaminated or of unknown age.

Inspect the Complete Firebird Cooling System

A new upper hose will not repair a weak radiator, defective thermostat or failing water pump. While servicing the hose, inspect:

• Lower radiator hose and internal support spring
• Radiator core and tanks
• Pressure cap
• Thermostat and housing
• Water pump
• Mechanical fan and clutch, if equipped
• Fan shroud
• Heater hoses
• Overflow hose
• Drive belts
• Coolant condition

Our complete cooling-system guide explains how these parts work together.

For an overheating Firebird, consult:

• Why a vehicle overheats while driving
• Seven signs of a failing radiator
• Bad thermostat versus bad water pump
• How to deal with engine overheating
• Can radiator stop-leak cause damage?
• When should you stop driving?

Frequently Asked Questions

What does MMHOSE-GM-15U fit?

It fits select 1967–1969 Pontiac Firebirds with the Pontiac 326, 350 or 400 V8 and compatible factory-style radiator connections.

Does the 326 hose fit every 1967 Firebird?

Only V8 cars with the matching cooling-system arrangement. It does not fit the factory inline-six configuration.

Does it fit a Pontiac 350?

Yes. It is listed for 1968–1969 Firebirds equipped with the Pontiac-built 350 V8.

Does it fit a Chevrolet 350 swap?

Not automatically. The Chevrolet small-block uses different cooling-system geometry. Select a hose based on the installed engine, water neck and radiator.

Does it fit a 1969 Trans Am?

It may fit an original-style 1969 Trans Am with the compatible Pontiac 400 cooling-system configuration. Verify radiator and thermostat-housing connections.

Is the lower hose included?

No. MMHOSE-GM-15U includes one upper radiator hose. The lower hose is a separate part.

Are clamps included?

Yes. Two worm-gear clamps are included.

Will it work with an aluminum radiator?

Yes, if the aluminum radiator retains the factory inlet location and correct diameter. Measure custom radiators before ordering.

Will this hose reduce engine temperature?

No. It improves hose durability and pressure tolerance, but actual coolant temperature depends on the radiator, thermostat, water pump, fan system, airflow and engine condition.

Product Specifications