Coolant Leaks: Finding External vs. Internal Leaks Before They Strand You
A slow coolant loss is a warning. We cover external leak sources and the internal leaks — EGR cooler, liner — that mean engine damage.
External leaks
External leaks are the easy ones — radiator seams, upper and lower hoses, water pump weep hole, heater core, and the coolant filter housing. We pressurize the system and watch for the leak, or use a UV dye if it's slow. Most external leaks are fixed with a hose, clamp, or fitting on the shoulder.
Internal leaks
Internal coolant loss — disappearing coolant with no visible leak — is more serious. The EGR cooler is the most common culprit (coolant into the exhaust or intake), followed by a cylinder liner leak (coolant into the oil), a head gasket, or an oil cooler failure. Coolant in the oil, white smoke, or a truck that builds pressure in the cooling system under load all point internal. We pressure-test, check for combustion gases in the coolant, and inspect the oil — because an internal leak left running will destroy the engine.
Why it matters fast
A truck losing coolant slowly will eventually overheat, but an EGR cooler dumping coolant into the exhaust can hydro-lock or wash down cylinder walls. We diagnose the source before topping off and sending the truck back out — a 'top it off and watch it' approach hides a failing cooler until it fails catastrophically.
Our mobile diesel technicians carry the tools and parts to diagnose and fix this on the shoulder or at your yard — 24/7/365 across Colorado, Wyoming, and Texas.
(303) 476-3622An overheating diesel will warp heads and crack liners in minutes. We cover the diagnosis path and why pulling over is non-negotiable.
A radiator that can't shed heat will overheat the truck under load. We cover external blockage, internal scale, and seam leaks.
The fan clutch engages the cooling fan when airflow is needed. When it fails, the truck overheats climbing grades or sitting still.