# Diesel Engine Cooling System Repair in Upland > Diesel pickup or van running hot on a grade? Route 66 Auto Repair in Upland pressure tests the whole cooling system and writes the estimate first. Source: https://route66autorepairshop.com/diesel-engine-services/diesel-engine-cooling-system-repair Updated: 2026-09-17 Business: Route 66 Auto Repair, 1775 W Foothill Blvd, Upland, CA 91786, (909) 608-7699 Hours: Monday to Friday 8 AM–5 PM, Saturday 8 AM–2 PM, Sunday closed **TLDR:** A diesel that runs hot under load usually has one weak link. We **pressure test the whole system**, find it, and label every line **need-now or need-later** on a written estimate. Diesel engine cooling system repair fixes the radiator, hoses, water pump, oil cooler and heat exchangers that keep a working diesel out of the red. Route 66 Auto Repair in Upland diagnoses light and medium-duty diesel pickups and vans that run hot towing up the Cajon Pass or idling on Foothill Blvd in August. ASE-certified technicians find where the heat or coolant is going and put the fix in a written estimate first. ## What are the signs a diesel cooling system is failing? - Gauge climbing on a grade, then settling on flat ground - Coolant level dropping with no puddle under the truck - Sweet smell or white vapor from the engine bay after a hard pull - The truck cutting power on its own to protect itself from heat - Crusty residue at hose ends or the water pump weep hole ## Why is a diesel cooling system different from a gas engine's? A diesel carries more coolant and rejects more heat into it. On many trucks that coolant also runs through the engine oil cooler, the transmission cooler and the EGR cooler (exhaust gas recirculation cooler). Leaks there can hide inside the engine instead of dripping. So we test the whole system instead of swapping the part that looks old. A pressure test, a combustion gas test and a [diesel engine diagnostics](https://route66autorepairshop.com/diesel-engine-services/diesel-engine-diagnostics) scan usually point to the real source. ## Our diesel cooling system repair process 1. **Listen and scan:** We note when the heat shows up and read temperature and fan data with a scan tool. 2. **Pressure and gas test:** The cold system is pressurized to its cap rating, and the coolant is checked for combustion gas. 3. **Trace the loss:** Hoses, clamps, radiator tanks, the water pump and the coolers are inspected, and failed parts are photographed. 4. **Repair and bleed:** Approved parts go in, the system is filled with the coolant your engine specifies, and trapped air is purged. 5. **Road test under load:** We drive until the fan cycles, then recheck for leaks. ## What's included in diesel cooling system repair - Cooling system pressure test and radiator cap test - Combustion gas check of the coolant - Scan of coolant temperature and fan command data - Photos of any leaking or cracked part - Coolant refill to spec and air purge - Load road test and final leak check ## Is it a need-now or need-later repair? **Need now:** - Gauge in the red or the truck derating for heat - Coolant loss you have to top off every trip - Coolant showing up in the oil **Need later:** - A slow seep at a hose clamp with a steady level - Coolant that tests weak but still looks clean - Soft or cracked hoses that still hold pressure ## How pricing and timing work Price depends on what failed and how deep it sits. A [radiator hose](https://route66autorepairshop.com/cooling-heating-ac-services/radiator-hose-replacement) is a short job; an EGR cooler can mean removing many parts first. The diagnostic fee is stated at the counter before testing and applies to approved related repair. AAA members save 10% on parts and labor, up to $75. Same-day work happens when the board allows, so call before you drive over. ## Aftercare Check the coolant level cold for the first week and watch the gauge on your first tow. Call us at [(909) 608-7699](tel:+19096087699) if it keeps falling. ## Frequently asked questions ### Can I keep driving my diesel if it only runs hot when towing? Short, unloaded trips are usually fine if the gauge stays normal. Towing is where heat warps heads and cracks coolers, so bring it in before your next trailer trip. ### Do you work on the diesel engine oil cooler too? Yes. It shares coolant with the engine on many trucks. If the tests point to it, see our [diesel engine oil cooler repair](https://route66autorepairshop.com/diesel-engine-services/diesel-engine-oil-cooler-repair) page for how we check and replace it. ### Will a coolant flush fix my overheating? Only if the coolant is the problem. A flush does not fix a failed fan clutch, a stuck thermostat or a blocked radiator. We test first and tell you whether a flush is worth it. --- Call (909) 608-7699 or visit https://route66autorepairshop.com/contact for a written estimate.