The patient is my '78 F250 with a recently rebuilt 460 I just installed. The truck has a two year old aluminum radiator and a brand new water pump. The thermostat is a couple years old as well, and with this radiator and thermostat my old engine ran at a little less than half on the temp gauge. Static ignition timing is set at 6° BTDC with the vacuum advance plugged and the spark plugs are brand new Motorcraft though I don't recall the plug numbers. The coolant level is probably a little less than 1" below the filler neck. I took compression readings today and all cylinders are at 155-165psi.

Now with this new engine if I idle it for 10 minutes or more the gauge goes past the half way mark, perhaps close to 2/3, and once fully warmed up it starts to miss and knock a bit. See the attached videos and let me know what it sounds like to you. It sounds like detonation to me due to the high temperature. Another clue is that I can only get ~15 psi of vacuum at the manifold with a vacuum gauge regardless of where I set the idle mixture. If I bump up the ignition timing up to 12-14° I can coax 16-17psi out of it. My tired old engine had 17-18psi at idle with only 120psi compression, so I'm pretty stumped. Perhaps I have air pockets in the cooling system?

Anyhow looking forward to y'alls expert analysis, thanks.

 

I tried, couldn't get sound.

I have a low tone rhythmic / regular noise at very low idle warmed up, I have listened with both a piece of hard wood stick (old night stick) held to my ear and carefully moved around, and a stethoscope. Pretty sure mine is fuel pump or the two piece eccentric. Mine is not a timing chain.

 

Yeаh you are right, it is hard to hear. It's a sporadic knocking sound that in the video sounds kind of like hitting a wooden stick on concrete. It's not a rhythmic sound at all like a fuel pump eccentric or something in the drive train would make. When it does happen it coincides with a slight misfire. I will try to get more videos tomorrow with better sound.

 

Hard to tell, kind of loke something floating around and making random contact. my first thought would be in the flex plate or torque convertor area. but that's a wild guess based on not much.

 

Yea tough to tell on the knock. Doesn't sound like a typical issue where it knocks every revolution. Can you tell is it coming from bottom end or towards top? Front or rear? Does it go away when rpm is increased? How is your oil pressure?

As far as low vacuum, make double sure there are no vacuum leaks? Was there a focus on a performance cam? If the engine can handle more intial timing without detonation when driving go ahead and increase it.
The only thing I can say for certain is you need a fan shroud.

 

I would want to make sure you are getting good coolant flow. You have probably done this already, but (from cold start) I would remove the radiator cap and let the engine warm up to the point that the thermostat opens up. This may help make sure that any trapped air bubbles have the ability to work out of the cooling system. (Burbing it.) Once the thermo opens watch to see that the coolant is coming into the top of the radiator and circulating. (Moving from left to right if I recall correctly. ) Now, of course, you have to be prepared to jam the radiator cap back on and/or shut the engine off as the coolant is getting hot now and is going to want to shoot up out of the radiator and scald you. So you really just get a quick view of the circulation.

 

I would hazard a guess of timing as well. Also pull plugs and check color. I real temp gauge would help. AFR gauge wouldn’t hurt either.

Could also be something bolted close to the engine that gets warm and gets loose.

You may be chasing a loose bolt somewhere.

 

I think your ignition timing is too slow. with the vaccum plugged you only have 6 degrees. my 400 runs twice that plus full time vaccuum of 12 degrees. Don';t know if that's related.

 

I don't see how it could be timing and be so random, there's no consistency. and if you were getting detonation at idle it would be hard to crank and it wouldn't run under load. maybe if you had plug wires shorting and firing the wrong cylinder at the wrong time. it would have to be something like that.

To me it sounds like something in a clothes drier banging around, like something loose in the oil pan maybe. but I can't imagine what that could be.

 

I know guys have already said about using a stethoscope, but getting an actual mechanics one would be really helpful. I use mine all the time on motors and it really helps to hear much better where a noise is coming from. Inexpensive tool that's super helpful. I'd be doing that to narrow down where the problem is..

 

I thought the same thing about the flex plate so I rechecked that and all four nuts were torqued down tight.

 

Oil pressure is good, though it drops a bit the warmer the engine gets. I really think I just have an air pocket in the cooling system because the knocking only occurs once the temp gauge gets past the halfway mark. The cam is an unknown factor in this engine, though there were no other performance mods made that I can see so I'm doubtful it's anything but a stock one. Also the idle is pretty mellow which makes me think it's a stock cam.

Agreed on the fan shroud (also as a safety factor), but as I said the previous engine ran much cooler with this radiator and no shroud and could idle all day long with the temp gauge sitting below half. The new radiator is smaller than my old stock one, so the original shroud won't work. I went round and round trying to find a new aluminum radiator the same size as the original, but no luck.

 

Excellent advice and I will do this. Is there an easy way to "burp" the air out? I was thinking of removing the temp sender from the manifold while it's cold.

 

The timing is very conservative and is I think part of the reason the vacuum is so low.
When I pulled the plugs to check compression they didn't show much color yet being brand new. If they are the wrong heat range they could be burning too hot though, I will check that out.
The stock temp gauge seems pretty accurate to me, what do you suggest?
I had no idea that AFR gauges even existed! Several of my vehicles will be getting one soon including this one!
Definitely not a loose bolt, the noise is internal.

 

I don't want to bump up the timing until I get the cooling situation figured out.