Overheating during engine break-in. Twice!
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Elder User
Joined: Apr 2015
Posts: 613
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From: Boston, KY
Overheating during engine break-in. Twice!
I just installed the engine I rebuilt and started to break in the cam. I ran initially with the radiator cap off, then put the cap on as I reached 190*. After a few minutes of running at 2500 rpm, the engine started to overheat, so I shut it off. The moment I shut it off, the radiator started violently spewing fluid out of the overflow. I shut it off, let it cool to 180*, then went back to try again after topping off the radiator. This time, I left the cap off. As soon as I started the engine, the temperature dropped to 160*, indicating that the cooler fluid that was sitting in the radiator had flowed into the engine. After a minute, the temperature climbed to 230* and I shut it off again. This time, without the cap ever having been put on, in spewed like a volcano and drenched my rafters. Why am I overheating, and why does the radiator only shoot fluid once the engine is turned off? I am stumped!
New User
Joined: Jul 2016
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Well, I ain't no expert and I'd certainly wait around for some more opinions. That said though I can tell you that temperatures typically rise once you shut down a motor. The air is not passing over the radiator as it was when the motor was on so you get a brief temperature Spike when she shut down. That impart good cause the volcano.
May be a stupid question but are you running straight water or 50/50 with coolant?
Lastly, when you rebuild the motor did you have it dunked? As in did you have it boiled out to make sure all the crud was out of every nook and cranny?
May be a stupid question but are you running straight water or 50/50 with coolant?
Lastly, when you rebuild the motor did you have it dunked? As in did you have it boiled out to make sure all the crud was out of every nook and cranny?
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Elder User
Joined: Apr 2015
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From: Boston, KY
The thermostat is new-ish. Less than a year old. Since the thermostat attaches to the intake on a 460, I did not disconnect the thermostat at any point during the rebuild. Just pulled the intake and set it on the bench until I was ready to put it back. I have a box fan in front of the truck blowing on the radiator.
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Elder User
Joined: Apr 2015
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From: Boston, KY
I would think that since the temperature dropped from 190 to 160 the instant I started the engine for the second time, that the thermostat was open and allowed coolant to flow into the engine. Am I thinking about that wrong?
Postmaster
Joined: Mar 2011
Posts: 2,698
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From: Taxachusetts
The thermostat is new-ish. Less than a year old. Since the thermostat attaches to the intake on a 460, I did not disconnect the thermostat at any point during the rebuild. Just pulled the intake and set it on the bench until I was ready to put it back. I have a box fan in front of the truck blowing on the radiator.
Just humor a grumpy old goat....if you're sure the T stat is good, please disregard....hahaha.
Did you pull the old water jacket plugs (not the freeze plugs but the square threaded ones) and clean out the block's innards?
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Postmaster
Joined: Mar 2011
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From: Taxachusetts
No, you're right about that...do you have a fan shroud?
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Elder User
Joined: Apr 2015
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From: Boston, KY
No fan shroud....there is a body lift so the fan is slightly offset from the radiator. Then again, this is the same setup I had before the rebuild and it never overheated. Is there a reason a new radiator would be the issue? I have a box fan sitting in front of the radiator, doing the break-in inside the garage.
Mountain Pass
Joined: Apr 2015
Posts: 247
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From: Conroe,TX
I will take a stab at this check the thermostat and how tight is the engine I know it is a fresh rebuild but maybe some of the clearances are to tight, on the violent eruption here is my theory. While the engine is running the water pump is keeping the flow going throughout the engine and lets say keeps the water in the engine when you shut the engine off well the water is no longer moving and maybe being on the point of boiling anyway shoots out the path of least resistance as it boils.
Logistics Pro
Joined: Mar 2005
Posts: 4,698
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From: Mexico, Missouri
I think I left my t-stat out when I broke my engine in, and also kept the water hose on just if it decided to overheat.
I've read where some have sprayed the radiator down while breaking in the engine with assistance of a helper.
I've read where some have sprayed the radiator down while breaking in the engine with assistance of a helper.
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Elder User
Joined: Apr 2015
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From: Boston, KY
My plan of action is to advance the timing, set the carb a bit richer, pull the truck into the driveway and have the wife spray down the radiator while it runs. Those seem to be the top three to try, according to the internet.
Logistics Pro
Joined: Aug 2010
Posts: 3,716
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From: Chillicothe
I'm voting that the lack of fan shroud is a likely culprit. Had a similar situation in the past during engine break in. That's the reason I only run water during a cam break in, less mess. We got around it by running a garden hose through a PVC adapter into the lower hose and just flushing the block with continuously freshwater for the break in. 8 years later the trucks still going strong.
pedant
Joined: Jan 2008
Posts: 23,576
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From: EXTREME southwest CT
What type of head gaskets did you use?
Is "front" front and only one facing 'up'?
The only time I've ever run into this is when my buddy put both gaskets facing up in his Bronco.
He went crazy with bigger radiators and high flow water pumps before he finally tore it back down.
Infrared guns are cheap now.
Makes it easy to find a hot spot.
There obviously is one, or it wouldn't be a volcano every time you shut it off.
Is "front" front and only one facing 'up'?
The only time I've ever run into this is when my buddy put both gaskets facing up in his Bronco.
He went crazy with bigger radiators and high flow water pumps before he finally tore it back down.
Infrared guns are cheap now.
Makes it easy to find a hot spot.
There obviously is one, or it wouldn't be a volcano every time you shut it off.
Cargo Master
Joined: May 2001
Posts: 3,208
Likes: 13
Did you replace the water pump. If you did. Did you put the metal plate between the block and pump. I have seen that before and will give you some really strange heat issues. And yes. If motor is tight they will run warm. And with no shroud and the fan not lined up with radiator. Then expect heat issues. So do the water on the radiator routine until you are ready to drive it. And if the timing is late they will run hot. So check the timing get it set and do your break in. If you added a zinc supplement to the oil then the break in is not that huge an issue. I never did like starting a new engine and running at 2000 + rpms for 30 mins. I prefer starting setting the timing then go drive them vary the speed and rpms up down. The biggest issue is if it has a new cam and lifters they need the zinc either in the oil or a coating of cam lube at installation.