Any Suggestions or Ideas?

[sir_veza]

Hello, Just throwing it out there in case anybody has experienced a similar issue.
The motor is a new 408 stroker, a year old with around 2K miles. The first two hour plus drive we took was a a couple of weeks ago. Sunny day. Outside temperature around 85 - 87 F.
After driving an hour and then two hours total the idle was choppy & rough @ 850 RPM. Oil pressure was low around 10 psi unless hitting the throttle which would raise it up to 30 psi. Engine temp 190 degrees (180 thermo) No fluid leaks of any kind. Brand new 20 50 conventional oil & Wix filter just done just before.

Here's a quick rundown of what's been done recently.
- New motor last August 2024.
- Existing Holley 750 (4160) carb
- Timing 36 degrees total
- New McLeod Super Street clutch & flywheel - Only when engine is hot clutch chatters occasionally in 1st gear
- New MSD Blaster coil
- New Mopar distributor (mechanical advance)
- New plugs & wires with heat sleaves for the headers
- Engine & headlight harnesses rewired recently (Evans Wiring harness)
Driving locally around town no issues on short drives.
Anybody had anything similar happen?
Thanks

 

[Challenger RTA]

I would check to see if the oil pump is working.
Pull the distributor and spin the pump to see if you have oil. It's a good tattle tell. The crank has to be turned for the cam to line up each side of the oil gallies.

 

[Challenger RTA]

Missing the hidden internal oil plug in the rear of the block. See picture below.

 

[sir_veza]

I would check to see if the oil pump is working.
Pull the distributor and spin the pump to see if you have oil. It's a good tattle tell. The crank has to be turned for the cam to line up each side of the oil gallies.



View attachment 143197

Thanks for the reply. Checked it. Oil pump seems fine. Also, at cold start on idle at 1200 RPM it's about 55 psi and driving around town it's well above 30 psi.

 

[sir_veza]

Missing the hidden internal oil plug in the rear of the block. See picture below.



View attachment 143194
View attachment 143195

Thanks for the reply. This is a virtually new motor. Oil pressure was fine until after driving at least an hour.

 

[Chryco Psycho]

For the choppy idle I would suggest using a Coolcarb spacer to drop the carb temp significantly .
water temp is good do you have an infrared temp gauge to check oil temp ? an oil cooler could help .

 

[sir_veza]

Thanks for the reply. Great suggestions. I do have a spacer but not sure if it's Coolcarb brand. Don't have an infrared temp gauge.

 

[WFHDANB426]

Hello, Just throwing it out there in case anybody has experienced a similar issue.
The motor is a new 408 stroker, a year old with around 2K miles. The first two hour plus drive we took was a a couple of weeks ago. Sunny day. Outside temperature around 85 - 87 F.
After driving an hour and then two hours total the idle was choppy & rough @ 850 RPM. Oil pressure was low around 10 psi unless hitting the throttle which would raise it up to 30 psi. Engine temp 190 degrees (180 thermo) No fluid leaks of any kind. Brand new 20 50 conventional oil & Wix filter just done just before.

Here's a quick rundown of what's been done recently.
- New motor last August 2024.
- Existing Holley 750 (4160) carb
- Timing 36 degrees total
- New McLeod Super Street clutch & flywheel - Only when engine is hot clutch chatters occasionally in 1st gear
- New MSD Blaster coil
- New Mopar distributor (mechanical advance)
- New plugs & wires with heat sleaves for the headers
- Engine & headlight harnesses rewired recently (Evans Wiring harness)
Driving locally around town no issues on short drives.
Anybody had anything similar happen?
Thanks

Has the oil pressure only been this low since the oil & filter change? The low oil pressure sounds concerning. In general every car should have a coiled wire in the lower rad hose to keep it from sucking closed at higher RPM'S like at highway speeds. Some lower hoses aren't form fitted and have an integrated wire to prevent collapsing. Are you running the factory 90 degree oil filter adapter?

 

[Cratos]

try changing the oil filter since the pressure drop started since you changed the oil. and see if the OP comes back up.10 psi a@ 850 is to low in my option.is it a stock or HP pump?

 

[WFHDANB426]

try changing the oil filter since the pressure drop started since you changed the oil. and see if the OP comes back up.10 psi a@ 850 is to low in my option.is it a stock or HP pump?

I agree starting with an oil filter change to even like a Fram PH8A to see if the pressure comes back up. Chrysler filters should have a relief valve built into them to still allow oil flow even when the oil is super cold, dirty, thick, etc. If the camshaft plate isn't tight and there isn't a pipe plug right behind it in the oil feed galley that could explain the pressure loss. A faulty oil pressure gauge. Loose oil pump bolts on the cap. Stuck relief valve in the pump. Cover coming loose on the pump. I would say to check with another gauge and replace the oil filter first. The two easiest things. Loose oil pickup tube? Pinched oil pressure gauge line unless it's an electric gauge?

 

[WFHDANB426]

Sorry I didn't mean pipe plug in the oil galley, I meant a hammer in frost plug.

 

[Xcudame]

The plug missing in Challenger RTA could be your culprit. Especially since you're using a nice heavy oil! The oil pressure is fine when cold and when it gets hot and things out a little, the pressure will drop with that plug missing! That plug can be installed by removing the oil pan and oil pump and rear main cap. Had the same thing happen decades ago when we were running a 70 Challenger Street Stock circle track car!

 

[WFHDANB426]

The plug missing in Challenger RTA could be your culprit. Especially since you're using a nice heavy oil! The oil pressure is fine when cold and when it gets hot and things out a little, the pressure will drop with that plug missing! That plug can be installed by removing the oil pan and oil pump and rear main cap. Had the same thing happen decades ago when we were running a 70 Challenger Street Stock circle track car!

I ran a Chrysler Kit Car circle track asphalt car. I built lots of 340 etc engines and I'm just trying to remember if that plug in the oil gallery diverts the oil through to the filter before it goes on to oil the whole engine, and without the plug the oil can bypass the filter and still go on and oil the engine unfiltered?

 

[GiantRobo]

After driving an hour and then two hours total the idle was choppy & rough @ 850 RPM. Oil pressure was low around 10 psi unless hitting the throttle which would raise it up to 30 psi. Engine temp 190 degrees (180 thermo

Just a hail mary in case none of the other things pan out... Had the same symptoms on a slightly-bored 383 with roller cam. Would drive around town just fine to shows, etc. Then took a 2+ hour trip. It felt like it was going to die when I got off the freeway and drove around. Struggling to run. 10psi or lower... After it cooled off was fine.

My father in law had an engine builder friend do the motor. The guy only did drag motors and made the tolerances too loose for a street motor. Couldn't tell until the oil ran hot for a long time and thinned. I stepped up to a thicker oil and it was okay after that.

You could check your motor build sheet to be safe.

 

[Daves69]

............Wix filter just done just before.

Maybe change it and cut the used one open to see what it's collected.

 

[WFHDANB426]

Just a hail mary in case none of the other things pan out... Had the same symptoms on a slightly-bored 383 with roller cam. Would drive around town just fine to shows, etc. Then took a 2+ hour trip. It felt like it was going to die when I got off the freeway and drove around. Struggling to run. 10psi or lower... After it cooled off was fine.

My father in law had an engine builder friend do the motor. The guy only did drag motors and made the tolerances too loose for a street motor. Couldn't tell until the oil ran hot for a long time and thinned. I stepped up to a thicker oil and it was okay after that.

You could check your motor build sheet to be safe.

Back in the day I ran Quaker State straight 30 Racing Oil and as the clevite rod bearings wore out during the year I would step up to Quaker State 50 wt Racing Oil. Now with the high quality synthetic oils I guess you can run lower pressures. I had a 340 that bent a pushrod on the drivers side and kicked the lifter out of the hole and even though the oil gallery was exposed wide open I still had 20 psi of oil pressure.

 

[WFHDANB426]

Maybe change it and cut the used one open to see what it's collected.

Good idea actually! Pass a magnet through the filter media too. Usually has tiny cast iron particles.