Puzzling external engine coolant leak. Front of passenger head.

2008 F350 210,000 miles. Stock.

It is leaking about a quart of coolant whenever it is shut off hot from the passenger side of the engine. The entire engine is dry on top and even underneath, except that coolant collects on a bolt head on the front of the passenger side head and then drips down onto the cross member.

The bolt is on the head itself. It is above the lower radiator hose outlet and the horizontal EGR cooler.

I can't figure out where the coolant is coming from to get on that bolt head. There doesn't seem to be anything with coolant near the bolt head. I don't want to risk pulling everything apart and not being able to find the source of the coolant.

The closest things to the bolt head are the oil cooler and filter module assembly and the engine front cover assembly.

Both EGR coolers seem dry. None of the radiator hoses seem to be leaking. There is no obvious leakage on the coolant pump.

Any idea where the coolant is coming from ?

Thanks

Water pump? Plastic tube for heate core could crack, best idea would be to pressure test it to see where it is coming from.

6.0 Tech said:

Water pump? Plastic tube for heate core could crack, best idea would be to pressure test it to see where it is coming from.

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If I get the engine hot and shut it off I can see it drip from the bolt head. But I can't see anything more than that without taking parts off.

Is it OK to pressurize a hot engine ? If the engine is cold, how does the thermostat being closed play into things ?

I'll try to get a picture of the bolt head tomorrow.

Could it be a pinhole leak in the upper rad hose ? Or a leak in the thermostat housing ?

Just took it for a drive. Everything looks dry at the end of the drive. There is rust on the vertical EGR cooler bracket, beneath the upper radiator hose connection. But the upper radiator hose appears dry.

It is amazing that an engine that looks dry everywhere can be losing so much coolant !

Is your upper radiator hose white or black at the thermostat? Pressurizing a hot engine is fine. And it doesnt matter if the tstat is open or not, as the system will be equally pressurized.

The hose is black.

Its probably the hose leaking then. Id change it and see if it fixes it. The ones that are white at the tstat housing have 2 orings instead of one. While you have the coolant drained, i would do the lower as well if it is still the black one. Just the engine side on the lower, the radiator side doesnt leak all that often.

You are saying that the lower rad hose is leaking at the thermostat ? If so, I agree. I just spent an hour looking things over and I was just going to post the same thing.

The highest rust spot is on the steel underneath that hose. And the leak doesn't happen until the truck gets fully warmed up, ie the thermostat opens up and starts circulating coolant through that hose. The coolant has to be weeping out the bottom of that hose at or near the thermostat housing.

At first I thought it was leaking out of the vertical EGR cooler, but the rust traces aren't in the right spot for that.

I'm going to put some paper towel under the hose and take it for a test drive to confirm.

If you are running elc coolant it should leave a white residue when the coolant dries, that may make it more obvious.

I packed that whole area with paper towel and then drove the truck, stopping to check every couple miles.

The leak is where the lower rad hose connects to the thermostat housing. That was the first paper towel to get wet. And then I actually saw a drip coming out of it.

I'm going to replace the hose this week.

Thanks for the help.

The lower hose doesn't connect to the thermostat housing, the upper hose does.

You are correct, it was the upper hose, not the lower hose. I replaced it and the leak stopped. No more coolant loss.