Engine knock worse on warm engine
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Senior User
Joined: Apr 2003
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From: Raleigh, NC
Engine knock worse on warm engine
Hi all.
I've been reviewing posts for fixing engine knock in my 89F150, 5.8L 351w. Doesn't happen at idle, but even under moderate acceleration at 35mph without a load its obvious. Just gets worse from there, like going uphill or with a load of mulch, tec., in the bed.
Been trying higher octane gas, plug wire re-routing, lowered timing, all without improving the situation.
I'm considering taking it to my mechanic to check codes, vaccuum, exhaust, etc., but first wanted to post in case someone has experienced this -- the knock seems to be temperature related. Its minimal when the engine's cold, then gradually worsens as I drive - any ideas on where to focus given this symptom?
-RLP
I've been reviewing posts for fixing engine knock in my 89F150, 5.8L 351w. Doesn't happen at idle, but even under moderate acceleration at 35mph without a load its obvious. Just gets worse from there, like going uphill or with a load of mulch, tec., in the bed.
Been trying higher octane gas, plug wire re-routing, lowered timing, all without improving the situation.
I'm considering taking it to my mechanic to check codes, vaccuum, exhaust, etc., but first wanted to post in case someone has experienced this -- the knock seems to be temperature related. Its minimal when the engine's cold, then gradually worsens as I drive - any ideas on where to focus given this symptom?
-RLP
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Joined: Apr 2004
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What weight oil, what brand filter? Any changes in those two recently?
The viscosity of oil decreases with temp. This allows oil to be pushed out of a bearing more easily. As bearing clearance increases, this gets worse, and the extra clearance produces a knock when the slack is taken up at TDC/BDC.
It is unlikely that this can be repaired with simply a bearing replacement. Once a knock starts, there is a question about crank wear & surface, & rod size. If it's a wrist pin, that requires the piston to be pulled, and they have to come out the top.
No magic available, I'm afraid....
The viscosity of oil decreases with temp. This allows oil to be pushed out of a bearing more easily. As bearing clearance increases, this gets worse, and the extra clearance produces a knock when the slack is taken up at TDC/BDC.
It is unlikely that this can be repaired with simply a bearing replacement. Once a knock starts, there is a question about crank wear & surface, & rod size. If it's a wrist pin, that requires the piston to be pulled, and they have to come out the top.
No magic available, I'm afraid....
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Senior User
Joined: Apr 2003
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From: Raleigh, NC
Oil is most likely 10-30, I'll check on that and the filter brand tonight.
So the scenario of hot oil pushing out of bearing more easily, along with increased clearance does make sense with the increase in knock as the engine comes up to temperature ? (rather than knock sensor, plug wires, ERG, bad gas, etc.)
If that's my problem I suppose the band aid would be heavier weight oil, and the real fix might be in the rods and or wrist pin (I'd leave that to my mechanic).
So the scenario of hot oil pushing out of bearing more easily, along with increased clearance does make sense with the increase in knock as the engine comes up to temperature ? (rather than knock sensor, plug wires, ERG, bad gas, etc.)
If that's my problem I suppose the band aid would be heavier weight oil, and the real fix might be in the rods and or wrist pin (I'd leave that to my mechanic).
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Senior User
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From: Raleigh, NC
I verified the oil is 10W-30 Exxon Superflo, and although I couldn't see the brand on the filter its product number is V1A filter --most likely Superflo (had it done at the local Exxon station)
Thanks for the info ..
RLP
Thanks for the info ..
RLP
Lead Driver
Joined: Nov 2002
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From: Concord, NC
And that motorcraft filter will magically fix the knocking? I wouldn't count on it...
First step would be to determine if it is knock caused by worn parts and large clearances or if it is a pre-ignition knock, or if it could even be an exhaust leak that sounds like a knock. Another good thing to check is the actual oil pressure.
First step would be to determine if it is knock caused by worn parts and large clearances or if it is a pre-ignition knock, or if it could even be an exhaust leak that sounds like a knock. Another good thing to check is the actual oil pressure.
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Senior User
Joined: Apr 2003
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From: Raleigh, NC
Yeah, the Superflo Exxon brand may or may not be important here, but I've been lazy past few years about doing my own basic maintenance like oil, plugs, etc. and go with whatever the shop stocks..maybe paying for it.
I've also noticed the plug wire set is not Motorcraft - I think Belton or something, I'll check it today.
Do y'all think an oil change to 10-40, 20-50, or an "oil thickener" is worth it as a temporary bandaid? My concern driving 500 miles in July for our summer vacation.
-RLP
I've also noticed the plug wire set is not Motorcraft - I think Belton or something, I'll check it today.
Do y'all think an oil change to 10-40, 20-50, or an "oil thickener" is worth it as a temporary bandaid? My concern driving 500 miles in July for our summer vacation.
-RLP
Senior User
Joined: Apr 2008
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From: South west Wisconsin
And that motorcraft filter will magically fix the knocking? I wouldn't count on it...
First step would be to determine if it is knock caused by worn parts and large clearances or if it is a pre-ignition knock, or if it could even be an exhaust leak that sounds like a knock. Another good thing to check is the actual oil pressure.
First step would be to determine if it is knock caused by worn parts and large clearances or if it is a pre-ignition knock, or if it could even be an exhaust leak that sounds like a knock. Another good thing to check is the actual oil pressure.
Have it checked to find out exactly what the knock is- if its fuel related, make adjustments, if its mechanical, do yourself a favor and fix it right the first time to avoid excessive costs later. Just my 2 cents!
Tuned
Joined: Aug 2007
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How many miles are on the engine?
I have a 1988 F250 351 that started making noise around 170,000. Oil pressure became non-exisitant at idle. I started using Lucas (first a quart and by 180,000 miles I was using 4 quarts). The heavy oil additive helped some but the engine was pretty worn out and in the end nothing worked except a rebuilt engine.
I have a 1988 F250 351 that started making noise around 170,000. Oil pressure became non-exisitant at idle. I started using Lucas (first a quart and by 180,000 miles I was using 4 quarts). The heavy oil additive helped some but the engine was pretty worn out and in the end nothing worked except a rebuilt engine.
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Joined: May 2006
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From: Apex, NC
Had the same problem with my '96 I-300. Fixed it cheap. The problem was temp related just as yours is. Finally figured out that the previous owner had been running without antifreeze. That caused a lot of rust to accumulate on the temp sensor, insulating it from the overheating engine. So the temp guage indicated a temp somewhere around the "R" on the word NORMAL. A new temp sensor and a big jug of Superflush did the trick.
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Senior User
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From: Raleigh, NC
I took my truck into the shop -went with fuel injection service, i.e. clean fuel system, throttle body (they used BG -44K cleaner) and then adjusted timing to factory spec. (it was off, I think set too low). Amazingly the knock has disappeared! Mechanic advised run one tank of 89 octane, then go back to 87 and see how it goes. Engine has 77,000 miles if the seller was honest - I've owned it for about 6 years.
-RLP
-RLP
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