2018 6.7 with coolant loss with no extrenal leaks

Steve Mutter · March 27, 2019

I got a 2018 f-350 6.7 with losing coolant 60 000km. Customer has come by 3 times to have coolant top up about 6 litres each time, good customer who takes care of his trucks.I have checked for external leaks and found none, oil level is not over full, trans oil looks red and is not over full, have pressure test with it running and found the cooling system holds a vacuum. Road tested with a pressure gauge and found when the truck is hot cooling system pressure spikes to around 25 psi, my gauge did go any higher so it may spike even higher. Took the egr cooler off today and pressure tested it, does not look clean from coolant and its holding pressure with the test gauge installed. Anyone out there run into anything like this ? Last thing I am going to do befor taking the heads off is pressure test it over night and check the glow plug holes for coolant, any input is appreciated.

Bruce Amacker · March 28, 2019

Hi Steve!

An oil analysis will tell you if there's coolant in the oil but won't really give you any definitive direction, Napa PN 4077 CQ/Wix PN 24077, $14USD/$35CD.

Look for discoloration in the ports of the exhaust manifolds as you tear down.

Leave pressure on it overnight, do a relative comp test first thing and see if anything looks wacky.

Probably nothing you didn't already think of...

Good Luck!

Keith Browning · March 28, 2019

I have no answer or advice for you other than what has been done and discussed. We had three of these in the shop in the last few months with no diagnosis. We pretty much made the same inspections and tests that you did but I don't think either of us noted any pressure spikes.

leavnon3rd · March 28, 2019

just had a 17 with a bad cylinder head gasket. truck was stock ( no performance parts/flash) YOU should be able to get it to build high cooling system pressure when the engines cold as well IF you have a gasket issue. I power braked it (f550 with a ultility box) and the pressure gauge would climb like a boost gauge.

Steve Mutter · March 31, 2019

Thanks for the reply's, will be tearing down the engine this week and will post what I find.

Steve Mutter · April 2, 2019

Found what looks like some aluminum debris that must have fell in between the head and the gasket when they put the engine together from new. Damaged the head surface so its getting one head for sure, I have a video but its on my phone. If I can find the time I will try and upload it.

Steve Mutter · April 14, 2019

Keith Browning · April 14, 2019

Aaaaand there you have it.

MANNY · April 28, 2021

On 4/14/2019 at 7:05 AM, Keith Browning said:

CHECK YOUR EGR COOLER THE 2 BIG O-RING SEAL LEAKING COOLANT THRU EXHAUST

On 3/27/2019 at 4:16 PM, Steve Mutter said:

I got a 2018 f-350 6.7 with losing coolant 60 000km. Customer has come by 3 times to have coolant top up about 6 litres each time, good customer who takes care of his trucks.I have checked for external leaks and found none, oil level is not over full, trans oil looks red and is not over full, have pressure test with it running and found the cooling system holds a vacuum. Road tested with a pressure gauge and found when the truck is hot cooling system pressure spikes to around 25 psi, my gauge did go any higher so it may spike even higher. Took the egr cooler off today and pressure tested it, does not look clean from coolant and its holding pressure with the test gauge installed. Anyone out there run into anything like this ? Last thing I am going to do befor taking the heads off is pressure test it over night and check the glow plug holes for coolant, any input is appreciated.