Why does my 2008–2010 Ford F-250 6.4 diesel keep leaking coolant from the radiator?

Short answer: On the 6.4L Power Stroke, radiators that leak again and again are a well-known problem. Ford's TSB 09-23-1 says malfunctioning (stuck-open, 'hyper-extended') thermostats can cause repeat radiator leaks on trucks built through September 14, 2009, and an earlier field fix added a venturi tee to the degas (coolant overflow) bottle. Have the thermostats tested when the radiator is replaced. Don't run it low on coolant: owners say it can damage the EGR cooler and engine.

Symptom: Coolant drips or puddles under the front of the truck, a falling level in the degas bottle, coolant crust on the radiator tanks, or a radiator that starts leaking again months after replacement.

What to check first

1. Check the degas bottle level cold and look for wet or crusted coolant on the radiator's side tanks.
2. Ask whether the venturi tee is installed on the degas bottle hoses. Owners link to photos of what it looks like.
3. When the radiator is replaced, insist on the thermostat test in TSB 09-23-1. The shop compares engine oil temperature (EOT) and engine coolant temperature (ECT) on a highway drive. If oil runs more than 8 °F hotter, or coolant swings 10–12 °F every 30 seconds, both thermostats get replaced too.
4. Keep every repair order. Coverage arguments in these threads came down to paperwork.

Likely causes

1. Stuck-open (hyper-extended) thermostats. Ford's TSB 09-23-1 says malfunctioning high temperature thermostats can cause repeat radiator leaks.
2. Radiator failure. Owners on Powerstroke.org replaced radiators multiple times, one on his third by 76,000 miles. A Ford master tech said nearly every 6.4 he looked at had a slightly leaking radiator and suspected the rigid radiator mounting.
3. Pressure spikes / missing venturi tee. Members asked whether trucks had the venturi tee update installed and said thermostats sticking caused pressure spikes.

What it usually costs

Owners were quoted $1,000, $1,250 (radiator and upper hose) and $1,500 at Ford dealers out of warranty. Some got radiators covered when the dealer hadn't done the venturi tee update or when thermostats were found at fault. Ford's TSB lists 3.0 hours of labor for the radiator, or 3.8 hours with both thermostats.

Is it safe to keep driving?

With a small seep and the level kept full, owners drove short-term while arranging repairs. Don't let it run low or overheat; members warned that low coolant can damage the EGR cooler and the engine. Tow it if the leak is big. Verify with a mechanic.

DIY or shop?

Shop for most owners, especially since the thermostat test needs a scan tool. Experienced DIYers replace radiators themselves; some owners went to aftermarket radiators.

Recalls, bulletins and complaints in plain words

• No recall covers the radiator.
• TSB 09-23-1 (technical service bulletin, a repair guide Ford sends dealers): 2008–2010 Super Duty 6.4L trucks built on or before September 14, 2009 may have repeat radiator leaks from malfunctioning high temperature thermostats. Dealers verify the leak, confirm the venturi tee is installed correctly (a field service action for trucks built on or before May 15, 2008), road-test while watching oil and coolant temperatures, and replace the radiator and, if needed, both thermostats.
• Recall 07V139 (2008 6.4L trucks, separate issue): excess hydrocarbons could overheat the diesel particulate filter. Dealers reprogram the engine computer. If your truck is part of this recall, the dealer fixes it for free.
• NHTSA complaints: 56 keyword-matched complaints for Ford F-250 and F-350 2008–2010 (of 694 unique complaints queried, NHTSA complaints API by model year, queried 2026-10-18; keywords: radiator, coolant, antifreeze, overheat, egr cooler, thermostat, degas) (NHTSA returned no complaint data for 2 model-year queries).

What owners report

• In 2008 Ford F-250 radiator issues on Powerstroke.org, an owner was on his third radiator at 76,000 miles and was told the radiator warranty was only 12 months/12,000 miles. Others reported the leaks, dealer quotes of $1,000 to $1,500, and arguments over coverage. A member posted the full TSB 09-23-1 procedure, another got a radiator replaced free by showing the dealer hadn't done the earlier update, and one owner at 31,000 miles had a leak even with the venturi tee done, so the dealer replaced the thermostats too.
• In TSB 09-23-01 radiator leaks on Ford Truck Enthusiasts, an owner shared the full bulletin, including the oil-versus-coolant temperature test and the thermostat and radiator part numbers.

My take

My advice as a former pre-purchase inspector: on a 6.4, I put a flashlight on the radiator tanks and the degas bottle before I even start it. Pink crust there means a radiator is in your near future, and you should ask whether the thermostats were ever done.

Vehicle focus: 2008–2010 Ford F-250 and F-350 Super Duty with the 6.4L Power Stroke diesel.

Safety / mechanic note

Running low on coolant can overheat a diesel and damage the EGR cooler and engine. Verify with a mechanic.