400 Internal leak
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Senior User
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From: Phoenix USA
400 Internal leak
I need some opinions. I've got a 79 F-150 4X4, with a 400 in it. It has started to push water out of the radiator, not overheat, it's pressure. The motor got hot twice last summer (went to the high point of normal on the factory gauge) and I think somethings hurt. Does the 400 have a weak point such as head or block crack, or head gasket? This truck was stored in the garage for seven years when I needed to put it back on the road again for a while. The truck only has 45,000 miles on it. I know it is going to have to be torn down, it's just a shame to do it.
Thanks
Thanks
Junior User
Joined: Jan 2003
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From: Billings USA
400 Internal leak
Lariat,I have noticed with my truck that it runs most of the time halfway on the gauge,and occasionally creeps up beyond "L",but most of the time when it spits out coolant is when I get to tinkering and top off the radiator.My truck seems to like the coolant about 1 1/2" below the neck.I wouldn't deem the engine in need of rebuild unless it has huge amounts of miles or is in constant red zone,even this could be caused by a radiator in need of TLC,you might also check your thermostat in boiling water to make sure it is opening when needed.With the truck sitting for extended times I would err on the side of the coolant being bad and flush the system,if you get lots of gunk take the radiator in to be professionally done.I might add that after having my radiator done I still experienced low heat output and it was because the gunk in the system had plugged my heater core.I never had the steam coming out of my ducts as many do.Just my thougths,John
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From: Phoenix USA
400 Internal leak
Thanks John
The truck is not overheating anymore. New four core rad., system completely flushed out, new thermostat that is working fine. There is an internal problem, head or block crack or head gasket. I was just trying to find out if one problem was more common than the rest.
The truck is not overheating anymore. New four core rad., system completely flushed out, new thermostat that is working fine. There is an internal problem, head or block crack or head gasket. I was just trying to find out if one problem was more common than the rest.
Junior User
Joined: Jan 2003
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From: Billings USA
400 Internal leak
Joe,I didn't fully understand your question,just gave my experience of owning a 79.I haven't personally heard of a problem concerning gaskets or cracks.The 400 block is pretty strong so I would weed out cracks.If you smell exhaust fumes in your antifreeze or smell a sweet tinged exhaust with white smoke or no heat from the heater then explore the head gaskets.A common sign is a very distinctive white ash on the spark plug.,or even a wet plug that looks as if it's not firing.John
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Joined: Aug 2002
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From: Minneapolis, MN
400 Internal leak
Another quick check would be when the engine is cold loosen and retighten the radiator cap (to make sure there's no pressure) then start the engine and rev it a couple times and shut it right off. It doesn't run long enough for the temp to expand the coolant but if there is an increase in pressure in the radiator it's probably coming from a combustion leak into the cooling system. If so, it's probably time to tear it down.
Just my $.02
Greg
Just my $.02
Greg
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400 Internal leak
If your gettting excessive amounts of pressure in your cooling system after you ran your engine hot it sounds like you have either a cracked or slightly warped head or a bad head gasket. It is possible to crack the head as to allow compression from the cylinder to escape into your water jackets. On the other hand its possible you got a gasket that due to getting hot has a bad spot in it an is letting compression by. You can find out by running a compression check on all your cylinders. Get the specs on what they should be, the check them all. If you have one cylinder with less compression or two that are the same and the rest are higher then you have found the problem. In general your compression should be the same or relative among all your cylinders.
Lead Driver
Joined: Nov 2000
Posts: 6,624
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From: Albuquerque
400 Internal leak
You could run it up to operating temp with the rad cap off and look and smell for exhaust gasses out of the radiator. Works better with the fan belt off.
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From: chicago burbs
400 Internal leak
have you checked the spark plugs for one or more that are very clean? this would be caused by a steam cleaning effect from coolant getting into the cylinder. also you might notice white smoke (steam) that does not fade away after engine is up to temp. a marginal head gasket may only leak once warmed up.
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Joined: Jan 2001
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From: Valley, NE
400 Internal leak
I too have had an internal coolant loss problem with my 77 400.
My truck has very low miles, however it was badly overheated once.
I was getting coolant into my engine oil, when changing oil there would be about a cup of coolant that would come out at the end.
My mechanic first checked the intake gasket and that was not the trouble, then he removed one head and found a cracked head.
I bought 2 heads and had one reconditioned, and installed on the drivers side. I thought the problem was solved, but I am still losing coolant, and found a little in the engine oil again last oil change. Now I suspect that both heads must have been cracked.
Has anyone else had this trouble? I am wondering if I should replace the other head, or am I pouring money down a rat hole here? The engine runs smoothly and has decent power otherwise.
Thanks Greg58
My truck has very low miles, however it was badly overheated once.
I was getting coolant into my engine oil, when changing oil there would be about a cup of coolant that would come out at the end.
My mechanic first checked the intake gasket and that was not the trouble, then he removed one head and found a cracked head.
I bought 2 heads and had one reconditioned, and installed on the drivers side. I thought the problem was solved, but I am still losing coolant, and found a little in the engine oil again last oil change. Now I suspect that both heads must have been cracked.
Has anyone else had this trouble? I am wondering if I should replace the other head, or am I pouring money down a rat hole here? The engine runs smoothly and has decent power otherwise.
Thanks Greg58
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Joined: Jan 2003
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From: Billings USA
400 Internal leak
Greg58,my experience with coolant in the system has been this:not neccessarily related to the 400,but when I've had coolant in the oil I've experienced loss of power and very rough starting and idleing probably due to fouled plug(s).I'm not questioning you or your mechanics abilities,but how was the original head determined to be cracked?And was it checked for levelness?My thoughts are that you may have received another head that wasn't level,not as worse as the original but still not flat.Most reputable machine shops in town can pressure test a head for cracks,but my experience leans towards warped heads.That's just my experience for what it's worth> John
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From: Minneapolis, MN
400 Internal leak
Greg58,
I would think the heads would be more susceptible to cracks than the block. If the coolant gets low there is still coolant in the block but the heads could have air pockets. Or if the engine got hot and cold water was added the block would be the first to get hit. Either could be possible. And of course the intake should be good since it's a dry intake. I know hindsight is 20/20 but when you were that close you should have checked both heads.
Since you are still getting coolant in the oil there must still be a leak.
As long as it's running smooth the leak probably isn't from the combustion area to the coolant but an exhaust analyzer held over the open radiator cap while running should find that pretty quick. I would plan on doing the other head. If it is the block leaking into the oil, some cooling system stop-leak might work.
2 more pennies for ya'.
Greg
I would think the heads would be more susceptible to cracks than the block. If the coolant gets low there is still coolant in the block but the heads could have air pockets. Or if the engine got hot and cold water was added the block would be the first to get hit. Either could be possible. And of course the intake should be good since it's a dry intake. I know hindsight is 20/20 but when you were that close you should have checked both heads.
Since you are still getting coolant in the oil there must still be a leak. As long as it's running smooth the leak probably isn't from the combustion area to the coolant but an exhaust analyzer held over the open radiator cap while running should find that pretty quick. I would plan on doing the other head. If it is the block leaking into the oil, some cooling system stop-leak might work.2 more pennies for ya'.
Greg
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Joined: Jan 2001
Posts: 199
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From: Valley, NE
400 Internal leak
Thanks for the replys.
My mechanic is an old school type, not up on the Computer stuff, and electronics and such. So this was right up his alley. He wouldn't put a used head on without having it magnafluxed, and then had it reconditioned, I don't know if that involved checking for flatness. I will ask him.
I bought the pair of heads from a friend who builds a lot of engines, and he thought the 400 is prone to having head cracks, but I have never seen anyone discussing it here before.
In hindsight, I wish I would have done both at once, since I only had $20 invested in the pair of heads. I think the idea of checking the radiator for exhaust gas is a good idea.
I have not tried stopleak, but I do use a lot of it in my Demo Derby hobby, but that is a different story.
Thanks again, Greg58
My mechanic is an old school type, not up on the Computer stuff, and electronics and such. So this was right up his alley. He wouldn't put a used head on without having it magnafluxed, and then had it reconditioned, I don't know if that involved checking for flatness. I will ask him.
I bought the pair of heads from a friend who builds a lot of engines, and he thought the 400 is prone to having head cracks, but I have never seen anyone discussing it here before.
In hindsight, I wish I would have done both at once, since I only had $20 invested in the pair of heads. I think the idea of checking the radiator for exhaust gas is a good idea.
I have not tried stopleak, but I do use a lot of it in my Demo Derby hobby, but that is a different story.
Thanks again, Greg58
Senior User
Joined: Nov 2002
Posts: 375
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400 Internal leak
Well yeah....The 400 or 351C head is prone to cracking usually right between the valve seats.........
apparently some of the 400 blocks were also prone to cracking but not the 79's....
have your motor block tested for internal combustion leaks....$25-$30....
apparently some of the 400 blocks were also prone to cracking but not the 79's....
have your motor block tested for internal combustion leaks....$25-$30....