Rough idle after extended driving, high temp?

[jcd9730]

First of all, I just got my first truck, a 72 c10 in December, and since then I've been creeping on this forum and learned a ton!

As to my problem, after extended driving, as in freeway speeds, my truck idles really rough, the oil pressure is way low, and it is hot, around 220. The oil pressure is only real low with it in drive at idle. In park or accelerating, the pressure is fine. If I put it in park, it will idle fine, but in drive, it will idle rough enough to die. This is only after extended driving. Short trips it runs perfect. II just adjusted timing, had the qjet rebuilt, new fuel pump, new fuel filter, new thermostat and radiator (albeit a crappy auto zone one). I have not changed the oil, and I know the oil pan is leaking slightly.

So my question is, why does it idle so rough after longer trips? And why so hot? And why does the oil pressure drop so low? This seems to be related to the oil pressure dropping at idle, or the high temp, but I've no idea the causs

And Secondly, oil seems to be leaking from around the valve cover on one side. Is there a gasket in the cover that could leak oil?

Thanks for all your help guys, yall have been a huge help this far!
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[trac209]

What is the oil pressure at idle and while driving? Hot oil will be thinner therefore have lower pressure. Some more engine info would be helpful to diagnose issues. Welcome
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[jcd9730]

I don't have any gages, I'm just going off the dash gauge. Cold to hot its about at the 1/4 to 1/2. When it drops way low and the idle gets rough, it's almost at the far left mark.

Again, it's only when I drive for 30 min or so at freeway speeds that the oil pressure will drop so low, and eve then only at idle in drive. Not in park in drive, and not when accelerating. And this is the only time when it idles terrible
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[trac209]

I would get some accurate gauges,oil and temp. And see where you are at. If the engine is overheating it will effect the idle and the overall running of the engine.
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[jcd9730]

Is 220 too high? Could the auto zone plastic radiator be the cause?
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[trac209]

Well 220 is high but how do you know it's 220 if you have no gauge ? Before you jump to conclusions about what's going on you have to find out for sure. Gauges first. Address problems after. You haven't said what engine you have so I really can't tell you anything about the radiator being the issue. When you have more info I'll be happy to help diagnose the problem.
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[njmedic3306]

Oil temp is usually low on a v8. Don't hold me to it but I want to say somewhere in the single digits when it's warm at low idle. I have a temp gauge and it runs somewhere around 190-200. I know it's working because the temp goes up then pops down indicating that the thermostat is functioning.

Also do you have a 2 core or 3 core radiator? Are the fins in good shape. If you are only having this problem at highway speeds it sounds like there is not enough air getting through the radiator. Also see if your fan clutch is working properly.

[jcd9730]

Oh it's got a gauge at the thermostat sorry. Normally around 180-195. It's a383 according to PO, but it's for sure a 350 cast.
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[trac209]

Ok we'll yes 220 at a gauge is hot,as long as that gauge is correct. Have you adjusted the timing? If the timing is off you will have a rough running engine at lower idle and have overheating issues. A hot engine will thin out the oil and give you lower oil pressure. That being said I would address the overheating first. The rad for a 383 should be at least a 3 row of proper size and have a shroud. Personally I would get a aluminum 2 row but its as thick as a 4 row in core size.
Get a timing light on there and check timing. I would start at 12 to 14 degrees btdc to start and go from there.
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[jcd9730]

It's a new radiator from auto zone. No idea how many cores, it didn't say. How do I check the fan clutch? The fan spins plenty fast right now.

Could this have to do with an apparent oil leak from around the valve cover?
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[jcd9730]

I just did the timing last week. It's around 10 degrees, and runs super smooth cruising around town. The freeway is another story however. How do I check how many cores this radiator has?
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[trac209]

Originally Posted by jcd9730

I just did the timing last week. It's around 10 degrees, and runs super smooth cruising around town. The freeway is another story however. How do I check how many cores this radiator has?
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With the engine cold open the cap and count how many rows thick the rad is. Or take a pic and post it and I or somebody else will tell you if your unsure. Pretty straight forward.
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[jcd9730]

Oh! Didn't know what all that was in there. I wanna say two... But I will double check. Would that make that much of a difference?
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[TBONE1964]

What is the idle RPM when the engine is warmed up? Not only will the oil pressure drop with heat, it will drop with RPM. I would check the timing again. Do it like this if you feel safe doing it this way:

Get the engine up to warmed up. loosen the distributor and advance the timing slowly (counter clockwise). Listen to the RPM. does the engine smooth out at idle? If so you may want to advance it a little. The engine should idle at around 750- 850 rpm's when warm. When you adjust timing while the engine is at idle you will find that sweet spot where it sounds the best. Although, you will have to make sure you dont have any spark knock and that it will start ok when it is warm/hot.

You may have a vacuum leak also. You can check by spraying a little shot of carb clean into the carb while the engine is running. If the rpm drops, you have no vacuum leak. If the rpm raises, then you have a vacuum leak somewhere.

On top of all of that, if you have a plastic tank radiator then it has an aluminum core and most likely has one long core instead of 2 or 3 cores like the old radiators had. Is this what auto zone gave you for a 72 chevy pick up? I cannot vision how that would even work in your truck but I don't think it has anything to do with your overheating unless you are not running a shroud and your fan is more than 4 inches from the radiator.

Just some thoughts.
Good Luck