Not your normal Mopar cooling issue

[Mopar Vince]

Most of the Mopars I've owned that have had cooling issues were the "gets hot idling in traffic" type.
But #projectvertfish has something different.
My BPE 408 runs great and stays cool (180 degrees) at idle and around town but climbs to 195-200 degrees at extended periods at 75 mph or above. 3500 rpm.
I'm thinking it might be lean issue.
Or possibly something to do with using the restrictive cast iron 273 manifolds.
Opinions welcomed.

 

[toolmanmike]

Yes. It's not overheating though.

 

[Mopar Vince]

Yes. It's not overheating though.

Yes, restrictive exhaust?
Yes, lean?
195-ish ok then?

 

[toolmanmike]

Yes, restrictive exhaust?
Yes, lean?
195-ish ok then?

Could be lean. You'd have to read plugs or plumb in a wideband o2 sensor. The 273 manifolds are definitely a restriction. As long as the engine doesn't climb to 230°+ you should be fine. It apparently climbs and stabilizes.

 

[Mopar Vince]

Could be lean. You'd have to read plugs or plumb in a wideband o2 sensor. The 273 manifolds are definitely a restriction. As long as the engine doesn't climb to 230°+ you should be fine. It apparently climbs and stabilizes.

Stable at just under 200

 

[jazak5]

get rid of those 273 ex manifolds !!! not doing that 408 any justice... nice car !!! By the photo. you cant tell me that you got cheap.... OR you used them because you don't trust yourself !!//restrictor plate/rev limiter ??

 

[brian6pac]

Yes get rid of the manifolds, even tri-y headers would be better. 200 degrees is fine but I would get a air/fuel meter and watch it for a while to see what you really have.

 

[CRUZE 418]

Could also be the lower radiator hose collapsing. Spring?

 

[AJ/FormS]

What are the spec on your cam and what centerline did you install it at?

More likely your ignition-timing is retarded
And the exhaust leaving the cylinders is still burning, and still expanding. And jamming up in the logs. Then on the overlap cycle, the HOT high pressure exhaust is racing across the piston and up into the intake, which is at waaaaaay less pressure.
And around and around and around it goes.

Here is your proof; the first few inches of the intake runners will be coated with a thic, cooked-on layer of black soot.

Here is your cure; With the car stopped and brakes locked, rev the engine up to cruise-rpm and hold it there. Then grab the distributor, and advance the timing until the rpm no longer increases. Now read the timing at your cruise rpm. Subtract 3 degrees and Write it down!
Let the engine return to idle and put the timing back to where it started.
Now, go figure out how to get that written-down number of cruise timing, without affecting your PowerTiming, and make it happen.

 

[brian6pac]

Could also be the lower radiator hose collapsing. Spring?

It will only collapse if there isn't any pressure in the system, as is a bad radiator cap. Does the system make pressure when the temp comes up ?

 

[Ccas]

I agree with all the comments above but one that was missed is that you may have a 'volume' issue. With a big motor and a small radiator at higher speeds, you don't have an air flow issue. The air is pushing through the radiator faster than any fan combination that exists. If you can get more fluid in the system, you can lower temps at speed.

 

[69FBCuda]

Fan clutch?

 

[CRUZE 418]

Doesn't need it at cruze speed.

 

[Mopar Vince]

It will only collapse if there isn't any pressure in the system, as is a bad radiator cap. Does the system make pressure when the temp comes up ?

I agree with all the comments above but one that was missed is that you may have a 'volume' issue. With a big motor and a small radiator at higher speeds, you don't have an air flow issue. The air is pushing through the radiator faster than any fan combination that exists. If you can get more fluid in the system, you can lower temps at speed.

I'm using this radiator from engineered cooling 22" Mopar BIG BLOCK HD Aluminum Radiator - Dual Fans And Aluminum Shroud and a milodon high flow water pump so I'm not sure fluid is an issue, but maybe.

 

[brian6pac]

The shroud is blocking the air through the rad at high speeds, your forcing the air through the 2 holes about 10" in diam each.

 

[yellow rose]

I'm using this radiator from engineered cooling 22" Mopar BIG BLOCK HD Aluminum Radiator - Dual Fans And Aluminum Shroud and a milodon high flow water pump so I'm not sure fluid is an issue, but maybe.

That should have a 26 inch radiator. As Ccas pointed out, you don’t have enough volume to keep the engine the same temp at cruise as you do at lower engine speeds.

The temp should not climb going down the highway. Perfect example of a radiator not doing its job.

I didn’t look at your links but as Brian pointed out, if that radiator has one of those flat shrouds on it, that is killing air flow at speed. Not good either.

 

[Ccas]

I'm using this radiator from engineered cooling 22" Mopar BIG BLOCK HD Aluminum Radiator - Dual Fans And Aluminum Shroud and a milodon high flow water pump so I'm not sure fluid is an issue, but maybe.

That's a dual 1" unit. I suffered from my personal car running hot for years. I tried everything including a 2 row 1" aluminum radiator. It helped but only delayed the steadily rising temps. Then I switched to a dual 1 1/4" aluminum radiator without changing anything else and problem went away. This was before Cold Case even existed. That being said, at 200 degrees, you really don't have a problem. At 3500 rpm and 75 mph, i'm sure that temperature bump is felt in the cabin and combined with the engine noise, may be a little annoying. However, It's only an 'overheating' problem if 200 becomes 210 and then 210 becomes 220 etc.