1994-1998 Dodge 5.9L Cummins Grid Heaters

The grid heater on the 1994-1998 Ram 5.9L Cummins

The 12-valve 5.9L Cummins is a direct-injection engine, and it does not use glow plugs. Instead, an electric grid heater sits in the intake stack between the cast air horn and the intake manifold, so incoming air passes across the heater element on its way into the head. Below about 59 degrees F, the system cycles in two stages: pre-heat before you crank and post-heat after the engine fires. The heater is switched through relays, and the relay wiring includes a fusible link.

What fails and why

Parts vendors who specialize in Dodge Cummins trucks treat grid heater relays and the heater element as wear items on 12-valves and stock them for that reason. This is a reported pattern rather than a documented factory bulletin, and it is tied to age, not a mileage number. It shows up two ways:

• Relay stuck on: the heater stays powered and can drain the batteries.
• Dead circuit: no intake heat in cold weather, so the truck starts hard and slow with white smoke.

On modified trucks there is a separate issue: the grid-heater plate, along with the single-inlet factory horn, becomes an airflow restriction once airflow rises. That is a horn and manifold question rather than a heater repair.

Stock replacement vs. upgrade

There is no performance upgrade for a grid heater. The goal is a circuit that heats when it is cold and stays off when it is not. XDP builds its grid heater relay fusible link wire as a heavy-duty part for 1994-2002 trucks. On the sealing side, the heater sits in the intake stack, so any time it comes out, reseal it with a fresh heater grid gasket such as the Mahle G32749. A leak there sits right in the boosted intake path.

What we carry

This page carries the XDP heavy-duty grid heater relay fusible link wire, listed for 1994-2002 5.9L Cummins trucks, and the Mahle G32749 intake heater grid gasket, listed for 1989-2007 5.9L Cummins engines.

Fitment notes

Grid-heater plates are not shared between the 12-valve and the 24-valve, and neither are the horns or manifolds. 1998 is a split year: Dodge moved to the 24-valve ISB with the VP44 pump partway through. Check the engine before you order: the 12-valve has the P7100 inline pump with a mechanical shutoff solenoid on top, while the 24-valve has the VP44 rotary pump with a wiring harness. The listing ranges on these parts run past 1998, but confirm the heater hardware on your engine before you buy. Cab, bed and drivetrain do not appear in these listings. Verify by VIN when in doubt.

Frequently asked questions

When does the grid heater come on?

When it is below about 59 degrees F. The system runs a pre-heat cycle before you start and a post-heat cycle after. On a warm day it may not cycle at all, and that is normal.

Can a bad grid heater relay drain my batteries?

Parts vendors who work on these trucks say yes: a relay that sticks on keeps the heater powered and can run the batteries down. It is a reported pattern, not a factory bulletin, so test the relay circuit before you buy parts.

Will a 24-valve grid heater fit my 12-valve?

No. The grid-heater plates differ between the 12-valve and the 24-valve, along with the horns and manifolds. On a 1998, identify the engine by its injection pump first.

Why does my truck blow white smoke on cold starts?

On this engine, a dead grid heater circuit is one cause: without intake heat, a cold start is slow and smoky. Check the relays, the fusible link wire and the heater element.

Not sure what fits? Call the shop at the number in the header, or use the fitment checker on any product page. We install everything we sell at our shop in Wildwood, FL.