4.6 2v Coolant loss question
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Mountain Pass
Joined: Nov 2021
Posts: 142
Likes: 14
4.6 2v Coolant loss question
Hi all,
I'm noticing the coolant level dropping and have some questions. Vehicle is a 2006 E250 with 350k miles on the chassis, ~150k miles on reman'd engine. Coolant is about a 1/2 inch low after 70 miles when engine is cold. Level is just above cold fill level when engine is hot.
I did a "block test" - negative. I figured intake manifold gasket was bad. My mechanic did a pressure test - 30 mins of no pressure loss at 18 psi. He doesn't think it's the intake gasket, wants me to keep an eye on it. One mechanic diagnosed blown HG from compression test. Second opinion disagreed, finding bad coil and spark plug causing 7 cylinder operation, plus three bad O2 sensors. Now I have a P0420 code indicating replacement of bank 1 cats. Power graph on diagnostic software shows even power across all 8 cylinders. No white smoke. No signs of coolant leaks. Do have occasional blue smoke, suspect valve stem seals.
Before I put a lot of money into replacing the cats, I want to be sure where the coolant is going.
I'm noticing the coolant level dropping and have some questions. Vehicle is a 2006 E250 with 350k miles on the chassis, ~150k miles on reman'd engine. Coolant is about a 1/2 inch low after 70 miles when engine is cold. Level is just above cold fill level when engine is hot.
I did a "block test" - negative. I figured intake manifold gasket was bad. My mechanic did a pressure test - 30 mins of no pressure loss at 18 psi. He doesn't think it's the intake gasket, wants me to keep an eye on it. One mechanic diagnosed blown HG from compression test. Second opinion disagreed, finding bad coil and spark plug causing 7 cylinder operation, plus three bad O2 sensors. Now I have a P0420 code indicating replacement of bank 1 cats. Power graph on diagnostic software shows even power across all 8 cylinders. No white smoke. No signs of coolant leaks. Do have occasional blue smoke, suspect valve stem seals.
Before I put a lot of money into replacing the cats, I want to be sure where the coolant is going.
- Will a pressure test show an intake manifold gasket leak?
- How much does coolant level fluctuate in your 4.6? Could this just be level fluctuation and I'm chasing my tail?
- Could this be the HG after all? Did you have a blown HG and have similar behavior?
- Has anyone had similar issue and would you be willing to share what it turned out to be?
Last edited by CyberEric; Nov 18, 2025 at 11:12 AM.
Cargo Master
Joined: Sep 2012
Posts: 2,112
Likes: 286
From: Eastern TN
Check that it's not going into the transmission! A pressure test should indicate if there's a leak but it's usually performed on a relatively cool engine. There might be a leak that only shows up at operating temperature. It's not fun to remove the plugs but comparing plugs and running an endoscope into the cylinders can reveal whether coolant is breaching the head gasket. I don't follow much 4.6 discussion but it seems manifold leaks are when, not if. There's a recent thread - https://www.ford-trucks.com/forums/1...150-4-6-a.html - where a member shared a picture showing coolant on one of the rear heater line junctions and @manicmechanic007 noticed a drippy manifold. Might be worth pulling the doghouse before spending on shop diagnosis. I'm guessing your E250 doesn't have a rear heater but rear heater cores are a known leak point on passenger vans. Ask the shop whether they recommend adding leak detecting dye to the coolant.
Sixto
07 E350 5.4 200k miles
Sixto
07 E350 5.4 200k miles
Last edited by tabijan; Nov 18, 2025 at 02:48 PM.
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Mountain Pass
Joined: Nov 2021
Posts: 142
Likes: 14
Thanks, I'll check out the thread.
I pulled the doghouse tonight. Spent 30 min looking around with a light with the engine running. Nothing. Dang.
You are correct that there is no longer a rear heater core, it was removed by previous owner. There are hoses going back there that just loop back. It's a lot of hose for nothing.
At a bit of a loss. I'll see what the shop thinks tomorrow. Hopefully they can be of support.
I pulled the doghouse tonight. Spent 30 min looking around with a light with the engine running. Nothing. Dang.
You are correct that there is no longer a rear heater core, it was removed by previous owner. There are hoses going back there that just loop back. It's a lot of hose for nothing.
At a bit of a loss. I'll see what the shop thinks tomorrow. Hopefully they can be of support.
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