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Kurt's 2020 McLaren 600LT | Diagnostic Case Study | FFP

Diagnostic Case Study

Kurt's 2020
McLaren 600LT

When a track-focused 600LT developed persistent overheating issues, FFP's Thorney Motorsport expertise uncovered what two dealers missed.

600LT

Model

M838T

Engine

Dyno Sessions

20+

Diagnostic Hours

Scroll

Vehicle 2020 McLaren 600LT Spider

Color Vega Blue

Engine 3.8L Twin-Turbo V8 (M838T)

Output 592 HP / 457 lb-ft

Mileage In 20,926 miles

Owner Location Reno, Nevada

Use Case Track Days / Hill Climb Events

// The Challenge //

Persistent Overheating

Kurt's 600LT was experiencing rapid temperature spikes during track sessions—even after just three laps. Multiple dealer visits yielded no answers.

🌡️

Symptom

Rapid temperature rise under high load conditions, limiting track time to just a few laps.

🏥

Prior Diagnosis

McLaren dealer replaced water pump, oil pump, and thermostats. Issue persisted.

⏱️

Duration

Problem developed over 3 years with progressive worsening over time.

🎯

Goal

Identify root cause and restore the 600LT to reliable track performance.

// The Investigation //

Diagnostic Timeline

A methodical approach to isolating the true cause of the overheating condition.

Phase 01 — TMS Inspection

Initial Assessment

Following the first dyno session, we identified that the main radiator fans were not activating unless prompted by the air conditioning system. Using our McLaren MDS scan tool, we attempted to manually trigger the fans but were unsuccessful.

Key Findings

Radiator fans not responding to ECU commands
Fans only activate when A/C system engaged
All fuses, relays, and wiring tested good
MDS scanner verified functional on other McLarens

Phase 02 — Circuit Analysis

Fan Circuit Deep Dive

We proceeded to inspect the fan circuit thoroughly. All related fuses, relays, and wiring were found to be in proper working condition. Our diagnostic procedures followed the OEM wiring diagram—no hardware faults were found.

Technical Analysis

ECU directly controls fan speed via PWM
Stock calibration should have 100% fan duty cycle
Previous tune may have altered fan control logic
Consulted with McLaren Customer Racing specialists

Phase 03 — Dyno Testing

M-Tuner Data Logging

Working with M Engineering, we installed data-logged software on the OEM ECU to track over 60 parameters. A custom MAP was created allowing fans to run at 100% regardless of throttle position or RPM—enabling us to isolate whether the cooling system itself was insufficient.

Dyno Protocol

4 dyno sessions with incremental testing
M-Tuner Live Map Switching Calibration Suite installed
M838T Motorsport Tuning Package applied
Temperature monitoring during sustained load

Phase 04 — Root Cause

CO2 Contamination Detected

After a hill climb event, the vehicle returned with worsening symptoms. At McLaren UK's request, we conducted a CO2 test on cold start. The test fluid turned green/yellow—indicating exhaust gases were leaking into the coolant system.

Critical Discovery

CO2 test positive on cold start
Combustion chamber leaking into coolant
Head gasket failure confirmed
Engine requires inspection/repair/replacement

// In The Shop //

Diagnostic Process

Final Diagnosis

Head Gasket Failure Confirmed

After exhaustive testing—ruling out radiators, water pump, oil pump, thermostats, turbochargers, downpipes, exhaust, transmission coolers, and all fluids—the CO2 contamination test revealed the true culprit: exhaust gases leaking into the coolant system from a compromised head gasket. This explains the rapid temperature rise under high boost applications that no amount of fan tuning could resolve.

// Services Completed //