First off the oil pressure gauge will read in the normal range until oil pressure drops below 7 psi, then it will read 0 because Ford uses a switch not a variable resistance sensor to monitor oil pressure. You need to find out where the coolant is going. Check for an external leak with a pressure checker and be sure to test the cap. Check the oil dipstick for evidence of moisture and use Carbon Dioxide test fluid (a trade name is Block Check) to test for combustion gas in the cooling system indicating a blown head gasket or cracked head. 460 engines run primarily at high rpm, like in a motorhome, had problems with the oil pickup in the pan cracking where it attaches to the block and allowing air to be sucked into the oil system, starving the engine for oil. When this engine starves for oil you will hear the lifters clacking first. There is an updated pickup. Also when an engine is overheating it will knock (spark knock/pre-ignition) because the air fuel charge is igniting early due to the heat in the cylinder. Could this be what you were hearing. No easy answers, you have a few things to check. Hope this helps.
* This post was
edited 03/16/12 10:22pm by pcassidy111 *
It could be as simple as an exhaust leak at the ex manifold which can sound surprisingly like a knock. Even more likely after someone has replaced it and perhaps not used high quality gaskets or followed directions exactly.
If it is a rod or mains knock, it won't show up in oil pressure or water temps until it's extremely bad. I've seen bad rod bearings be abused for a 10k plus miles before letting go. Of course if you wait a long time then the crank and rod may be junk.
Scott, Grace and Wesly
2003 Dodge 3500 4x4, 6 speed Cummins (lightly bombed),
2004 Forest River 25RKS many, many mods.
H0NDA eu2000i
There should be no gasket between the exhaust manifold and the cylinder head, it will fail. The 460 does not use an exhaust manifold gasket or any type of sealer, it is a metal to metal fit up.
John&Joey wrote: Just wondering what weight oil are you running.
I'm using Shell Rotella T Triple Protection 15w40
Good stuff. Was afraid you might be running that sewing machine oil that get's talked about on this forum for your 460. So many read the forum and then think what's good for the V10 is also good for the V8.
Also the 460 is not a high rev engine. That post I think was repeating what they read about the V10
The 460 is OBDI not II. It has very limited info to display. Good to check, but don't expect a lot.
There are many out there that are still running the 460 and are rock solid. So let's go back to basics. I read your prior posts about your rebuild, so that is going to put some more meat into the stew though.
A knocking sound can come from the lower end when a main rod bearing is shot. You would hear that all the time, but mostly under load.
You sat at a light and heard it (no load) and it went away when you took off (load). OK, maybe the oil pressure came up, but then again no oil light came on at the light either and the guage didn't indicate an issue.
So what can make a sound like that. Well when an engine isn't running on all cyclinders that thing can really thunk. What can cause that, well the two biggies, gas and spark. Change the gas filter, and check the spark plug cables for a burn thru. Things were good when you left home. While on your trip you're getting unknown gas and putting a lot of heat into the engine bay. These are the simple stuff which need to be checked first.
Again, the loss of antifreeze is disturbing. Maybe it's not related and is another issue all together. But, it isn't a good sign.
After reading the description of your plight, the best WAG I’d offer was. It sound’s like you’re experiencing a run hot or over-heating issue.
I don’t think your noise is due to motor lube concerns. Once a rod, main or w-pin gain enough clearance to knock under load, they stay knocking under load. Plus if low oil pressure scenario was occurring, the valve train would clatter long before the lower end joins in the cacophony.
I’ve seen a lot of well maintained 7.5’s break the ¼ million mile mark before needing rebuild or retirement.
I believe, pcassidy111 is most correct, stating the possibility of “running hot pre-detonation” as the source of your motor rattle. If you can load the engine by brake torquing the motor, while it’s still cool and it seems normal sounding, then I’d look into solving your motor’s running hot problem.
The Ford 7.5L hates running hot. If my MH did what your’s did on a trip and was later, quiet, under a cool torque and I was now safely off the road for a few days, I’d do at least the following, in whatever order seems prudent.
Check and repair any coolant leaks.
Check the radiator’s tank for slime on the interior walls. (Flush or get flushed if needed)
Check the radiator’s cooling fins for good attachment. (Renew unit if needed, and if so, forget the flush)
Check the coolant for at least a 50/50 mix.(Maybe add a wetting agent to the mix)
Renew the thermostat. (Known to screw up after overheats and could be one of the initial causes.)
Renew the cap with the correct OEM stated pressure. (This you already know)
Check the fan clutch. (The fan blade should free-wheel when cold and feel tight to move when hot and have very little lateral wobble. Check with engine off, of course.)
My 460’s rad fan clutch, made quite a noticeable roar every time it engaged. (Especially when climbing a long grade at wot)
And last but not least, hopefully, enjoy the trip to Texas.
Sorry if this post seems long, I lacked the time to make it shorter.
almost quote from S.L. Clemens
Don & Linda
1st RV UL EMS 4s Dome
2nd RV 21' AMF Scamper TT PV D300 Dodge
3rd RV National Seabreeze 133LX w/Demco Dolly
4th RV Jayco 2450 5TH PV Ford F-250 SD
After reading the description of your plight, the best WAG I’d offer was. It sound’s like you’re experiencing a run hot or over-heating issue...
As a sidebar to the above:
I've ran with a 40mph tail wind where my guage was showing the 460 was running as cool as can be. Then all of the sudden the fan kicked in. The fan is bi-metal and work on the air temp in the bay. With that high of a tail wind not much was going thru the bay.
Long story short, even though your guage showed normal, your bay temp may have been off the scale.
yep as previously stated by a mechanic, I think you done went and blowed the radiator cap.
I am inclined to go along with the overheating crowd. I don't really think that bringing it up to operating temp without pulling would give a true test of the cooling system's capability to get rid of the heat generated by working hard.
You got a real head scratcher there with an intermittent condition.
Also I am of the opinion that you did the right thing just fixing what was broke the first time.
I had a header crack one time at the junction of the pipe and the attachment flange and did it ever make an unusual slapping sound.
Hang in there, don't try the Saluda mountain grade again until you get it fixed, and good luck.
Check the fan clutch. (The fan blade should free-wheel when cold and feel tight to move when hot and have very little lateral wobble. Check with engine off, of course.)
My 460’s rad fan clutch, made quite a noticeable roar every time it engaged. (Especially when climbing a long grade at wot)
Now that you mention it I didn't hear the 747 roar from the fan clutch, sometimes you don't notice what you don't hear. I did replace the clutch fan when we did the heads but it wouldn't be the first faulty part I've purchased. Although since adding the headers I've noticed the whole dog house area seems to be much cooler over all then it ever was with the manifolds.
Right now, I'm going on the assumption that the loss of antifreeze was from the cap as I can find no other leaks. We’ll take it easy heading to Texas planning on not exceeding 300 miles a day. Once in Texas I’ll have a shop if need be to work in which will be a huge improvement over working with limited tools in an RV park.
Thanks to everyone for your thoughts and advice. We’ll keep you informed.
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