408 still overheating :/

Hi all,

I just put my new engine together:

1976 360 block 0.30 over
Scat cast steel crank
Scat I-beam rods
+5cc flattop pistons
windage tray
Melling HV oil pump
Rapom alu heads 2.02 intake 1.60 exhaust valves 65cc
Comp hydraulic flattapped xe274 cam
Edelbrock air-gap intake
about 10.6 to 1 compression
Hughes 2500 stall converter
TF-904 reverse full manual valve body
8 3/4 with 3.23 to 1
Car is 1974 Plymouth Scamp

and its still running too hot (yes i checked with infrared too) on hot days up to 250 degree...

what i did until now:

Checked 180 degree thermostat - works fine but i throwed it out think i had trapped air in the motor (already heard something about drilling a little hole in it??)

Changed the 26" griffin aluminium radiator with the original one - no improvement

Changed the milodon high volume water pump with the original one - no difference

Spring in the lower radiator hose

throwed my custom made fan shroud out
Has now only an electrical fan behind the radiator but i think when the car is moving it should work without a shroud (heard even without a fan because the fan is only for cooling when the car is not moving?)
The motor is running hot even when im just cruising down the street with nearly no throttle

Carb is a holley 650cfm DP now with bigger jets from a 750cfm hp main body because i thought it was too lean but also no difference still running hot

Any ideas what i should do next??
Thinking of an engine oil cooler just have the stock oil pan but with a dual oil filter relocation kit with two tall filters??

Thanks, Laurin

Water pump pulley too big not turning the pump fast enough...I put a smaller dia one on, cured my problem.

lomchivok said:

Water pump pulley too big not turning the pump fast enough...I put a smaller dia one on, cured my problem.

Click to expand...

When you were looking for a smaller diameter pulley, what year did you use and what where the sizes before and after?

You can drill 2 (1/16") holes on the thermostat. This will help air work its way out of the system. I have always done it.

Something like this:


Stock size crank pulley and water pump pulley?

Don't remember off hand but 3/16ths smaller rings a bell. The car is in storage 40 miles away but the old pulley is in storage with it. I'll measure Monday on my way home from work.
Edit: my pump is an 8 vane impeller. Changing from 6 to 8 vane didn't help much. The pulley was the fix.
Mine is a 408 too. Same pulleys were swapped from the 318 to the 408. The 318 ran cool the 408 didn't till I swapped the pulley.
The length of the pulley was shorter too. I turned out a brass spacer on the lathe to make the grooves line up...come to think of it I think 3/16ths is what the spacer was...maybe that's why 3/16ths rings a bell or was it 3/8ths...lol. I don't remember...I'm old.

have you bled the system? That seems to get looked over often times

This may or may not help but we're is the timing set. Not enough timing or having the timing locked out can cause the engine to run hotter than it should. Depending on the quality of your fuel you may need more timing not less and you may want to run a vacuum advance to help with timing at cruise rpm. Just my 1 1/2 cents good luck

I have a very similar setup in my 416 with 274-S cam, ebrock 7066 heads (65cc measured), Icon 20.5cc dish pistons, 160 degree milodon T-stat.

I run 91 octane pump gas.

What gas are you running?

On my engine, measured and cc everything and got ~9.7:1 compression. I'm at 32 degrees total timing. With just a couple degrees more timing I'll ping on hot 90+ deg day up a steep grade under acceleration.

What's your initial and total timing?

IMHO, if you are running pump gas, you have too much compression. It might not be 100% of your problem, you'll be always fighting it.

Well I see the original poster is in Austria. I think they have higher octane pump gas there

But with the info given I get this for static compression with std Fel Pro gasket kit and zero deck height.

11.18 to 1

found the pulley dia from my ebay purchase.
Mopar single grove fan, water pump, pulley. 5-5/8" diameter x 2-3/16" deep

I bet it's your pulleys also. Do you have to run catalytic converters there?

What is the timing set to?
If it runs hot all the time it could be pinging
If it runs hot only in park, sitting while running....then it's a coolant flow issue where a higher flow water pump, sometimes bigger fan will help that issue.

I check the temp at the heads when using a temp gun.

Where is the temperature being checked? It should be checked on the thermostat housing and upper radiator for a number that can be compared to other cars.

Make sure your temperature gauge is accurate and that your conversion from degrees C to degrees F are accurate.

This is a high compression engine. That means the combustion temperatures are a few hundred degrees F hotter than for low compression. This puts more heat directly into the heads and block and manifolds. More heat will go into the coolant too, but the air in the engine compartment is going to be much hotter over all because of the direct heat conduction through the engine. With AL heads, they conduct heat even better than iron heads and so there is even more heat conducted directly into the engine compartment air. Headers make the engine compartment air even hotter.

Putting in larger radiator in this case will not help too much because that is not where much the heat is going. I suspect that the heat is just building up in the engine compartment and needs to be ventilated out. As an easy experiment, cut and drill some flat steel plates to use to raise the rear of the hood about 20 mm at the stock hinges. This will create a gap in the back of the hood through which the hot air can better escape. And, it will increase cool airflow through the radiator. If this works, then you can make a better long term solution for this problem.

I had this problem in my turbo 2.6L Mitsubishi Starion rally car, and raising the back of the hood by < 20 mm dropped engine temperatures by 15-20 degree F on rally stages.

Ok well, a 408 @ 11.18 Scr still only makes a Dcr of 9.0 @188psi with an ICA of 63*( in at 106)
So; I have run about that, in my aluminum-headed 367 with zero overheating. And on 87E10. I ran 11.3 with the 292/108@ ICA of 74,70,and 66
So I think as to compression you're ok, especially since you say just taking it easy. Think of it this way; when running easy on the primaries, your VE is down at say 30%. So the EFFECTIVE compression ratio might only be a fraction of that 11.18;that is to say, the cylinder pressure will be way down. So this is not a compression ratio issue.At least not one that I can see.
Cruising down the street at nearly no throttle, implies below 30 mph. With 3.23s and say 2nd gear, this should be about 1800rpm with a TC that does not lock-up until 2500ish. Ok so if your tach is showing rpm that low, or anything lower than about 2300(that's a guess), then that could be a problem. That means the TC is smashing fluid around inside of itself and creating a lot of heat.And it's worse in 3rd. So the first thing I would do, is to put it in first and run the tach up to 2500.Which should be 24mph@5% slip. Now see if it overheats in the same manner as before.
If no it seems a lot better, then get a great big thermostatically controlled trans-cooler, and take the lines off the radiator.
But if it still has trouble, then either the rad is not shedding the heat, or the air is not passing thru it.
here>But the first thing I would do is put an anti-cavitation plate on an 8-vane impeller, and install that pump. The second thing I would do is gut an old thermostat and install that into the housing, as a restrictor. And the third thing I would do is run fresh air to the carb.If she's sucking in air at 400 degrees, and the engine is compressing that to who knows what, then reacting it, and the exhaust leaves the cylinders at 600* instead 400*, well you get the picture; you have created a big 'ol heat pump.
So after the engine is getting fresh air, then put a 7 blade direct drive fan on that pump and re-install the shroud.
Now try that 24mph cruise in first again.Make sure the timing is at least 40* from all sources (including the Vcan).
Make sure the electric fan is on the workbench.
If you have A/C, um you shoulda mentioned that. If you do; Back up the bus all the way to here. do those two things and then take out the condenser, and repeat the 24@2500 test.If that shows a heckof an improvement you will have to eyeball that condenser; air has to pass thru it pretty freely.
But I would still do all the other improvements,one atta time, until the cooking stops.
Then I would try it in second gear, still at 24 mph. If it cooks, install that trans-oil cooler.
Don't forget minimum 40* at 2500 at light throttle.

Lots of unanswered questions here. Would be good if we could get some answers so we could get caught up.

Ok wow thanks for all the answers and ideas!

lomchivok said:

Water pump pulley too big not turning the pump fast enough...I put a smaller dia one on, cured my problem.

Click to expand...

what pulley do you have? Currently im running the original one from my 318 who was in the car before.

68cuder said:

have you bled the system? That seems to get looked over often times

Click to expand...

How do you do it? I just put my front in the air that the radiator is higher than the engine and run the engine a few times without the radiator cap and leave it open for a few hours?

autoxcuda said:

I have a very similar setup in my 416 with 274-S cam, ebrock 7066 heads (65cc measured), Icon 20.5cc dish pistons, 160 degree milodon T-stat.

I run 91 octane pump gas.

What gas are you running?

On my engine, measured and cc everything and got ~9.7:1 compression. I'm at 32 degrees total timing. With just a couple degrees more timing I'll ping on hot 90+ deg day up a steep grade under acceleration.

What's your initial and total timing?

IMHO, if you are running pump gas, you have too much compression. It might not be 100% of your problem, you'll be always fighting it.

Click to expand...

We have good fuel in europe so i dont think the compression should be a problem.
Timing should be ok but i dont remember what it was - a friend of me checked it 2 or 3 times, he is running a ford 408stroker with about 11.5 to 1 compression and it runs fine with the same fuel.

lsm360 said:

I bet it's your pulleys also. Do you have to run catalytic converters there?

Click to expand...

No converter for cars 25years and older ;)

Temp. was always checked at the thermostat housing - there is alsonthe sending unit for the gauge.


But i remember i was alwas driving with about 60km/h in 3rd gear so and when i was driving 100km/h with nearly no throttle the temp. came down a little but still too hot

1974scamp said:

what pulley do you have? Currently im running the original one from my 318 who was in the car before.

Click to expand...

was the car an a/c car? if so is it still an a/c car ?

abodyjoe said:

was the car an a/c car? if so is it still an a/c car ?

Click to expand...

No was no A/C car.

But i dont know if the pulley is the one who came with the car because the 318 is from 1969 and the car is 1974

nm9stheham said:

Putting in larger radiator in this case will not help too much because that is not where much the heat is going. I suspect that the heat is just building up in the engine compartment and needs to be ventilated out. As an easy experiment, cut and drill some flat steel plates to use to raise the rear of the hood about 20 mm at the stock hinges. This will create a gap in the back of the hood through which the hot air can better escape. And, it will increase cool airflow through the radiator. If this works, then you can make a better long term solution for this problem.

Click to expand...

Good idea nm9! Or just run the car without hood for some testing. When you then have lower temperatures at all speeds you know how to proceed. The fact that a lot of your changes didn't do anything to the temperatures makes me think that something fundamental is off.
I had a similar problem in my E-body (long gone) with a much lesser engine, but then it simply was the original radiator --> bad "connections" between the mesh and the water channels of the radiator.

ok so for a 74 scamp (assuming thats what you are working on) with 318 and no a/c these are the pulleys it should have.. 69 would be different. not sure if its the issue but worth looking in to..

just use the pics as a guide. i'm not telling you to buy these new ones..

Hi,

Hemi466 is right on IMO. I had the same issue. I changed my vacuum advance source to "manifold", which in turn adds some timing at idle the car instantly ran cooler. Also Adding a set of SPAL Fans over the stock fans that Champion provided took the engine to another level of cooling. 179 degrees at stoplight idle and 183 degrees @ 3100 rpm on the interstate. I was at 213 at a stop light and 196 @ 3100 on the interstate. Changing the vac source made a huge difference! Ported vac by design is intended to increase engine temps on the smog engines to burn up left over hydrocarbons and reduce emissions. There are many articles online by experts that outline this much better than I can.

FYI,
Marion

hemi446 said:

This may or may not help but we're is the timing set. Not enough timing or having the timing locked out can cause the engine to run hotter than it should. Depending on the quality of your fuel you may need more timing not less and you may want to run a vacuum advance to help with timing at cruise rpm. Just my 1 1/2 cents good luck

Click to expand...

1974scamp said:

But i remember i was alwas driving with about 60km/h in 3rd gear so and when i was driving 100km/h with nearly no throttle the temp. came down a little but still too hot

Click to expand...

100kph in third, with 3.23s is about 2488 no slip, so the TC is now nearly locked.If the temp only came down a little, then the TC may not be the source of the hi-temps. But at 100 the ram-air effect thru the rad SHOULD be cooling the rad pretty good. Because it does not, by this time (2500),
there are really only three possibilities;
A) the brand new Griffen isn't doing it's job, or B) the water isn't circulating, or C)the air is going around the rad.


By 100kph a properly functioning rad with air being rammed thru it, and the pump moving the coolant, it should be cooling very well. You got 2500ish rpm. That's lots of waterpump speed, no matter what the ratio,the number of impeller vanes or with/without the anti-cav plate.It shouldn't matter.
Also no matter what fan is being run.
And the throttle is; "with nearly no throttle", indicating to me that the timing has got to be close,and it ain't lean; cuz the engine is hardly working.
And the TC is as good as locked.
And even if the carb is sucking hot underhood air, by this roadspeed the underhood air-temp should be down to nearly the coolant temp.

So my best guess is lack of air-flow thru the rad.
Make sure the front of the rad sees the incoming air, and that the rad is sealed to the core support. It helps to seal the hood to the top of the core support.Make sure the air can get out the back of the rad and is able to exit the chassis. As in no full belly-pan! I have a small skid plate is on mine, and seems to be OK.

here's a sort of test; With a cold engine and engine off; direct a small water stream into the rad fins, from a straight-on angle; the stream should come out the back nearly as strong as it entered.

As to the bypass hose; I restricted mine to force the coolant to mostly stay in the main circuit.That seemed to help too. You might need a hi-flow stat tho. I already had one.

AJ/FormS said:

So my best guess is lack of air-flow thru the rad

Click to expand...

thats what it sounds like... its overheating everywhere.. so the rads aren't doing their job, water isn't circulating or the air isn't going over the core properly..

like you said, shouldn't need a fan at all at 60 mph. air flowing through the core should cool it fine..

Well I can give my experience with my overheating and not overheating problems. I have believe it's pretty much a stock radiator and put a shroud with two electric fans behind it. I usually pretty much gut my thermostat so it's more of a restrictor than an actual opening and closing thermostat. Now my first 318 had to stock water pump with the stock fan actually and that all work fine and never overheated. Then when I put the 410 stroker in I actually used in electric water pump. I also just use straight water with one bottle of Redline water wetter. Never had any overheating problems with the Stroker motor. I just pulled that out a couple months ago for funsies and put a 318 in for my wife and it has a high-volume water pump. The first thing it started doing was overheating and sucking the bottom radiator hose closed. And of course first thing I did was get a better hose for the bottom that didn't collapse. The one with the spring was kind of expensive and I didn't like the spring in there that just corrodes anyways or rust. They actually had a cheaper alternative that was just a more stronger hose as if the spring was built into the rubber. it stays a little hot a lot of times especially when it's really hot outside and one time I had it overheat on the way home from the dragstrip an extremely hot afternoon. It could just be a lack of radiator and or it could be that the water's flowing too fast and not transferring? But all in all it was definitely the electric water pump that didn't allow my stroker to overheat. It seems like that was the factor. Of course I use a higher octane fuel with the Stroker because of the compression. Both of them are set at about 35 degrees Timing. I'm the last one to tell you to buy something that's for sure because you know how us Yanks are we love to spend money. One thing I ran into with the current 318 the previous owner or maybe the owner before him was a big fan of that crap called radiator stop leak! That block was clogged so full of crap I'm not sure if I got all out of there at this point. Anyways that's my experience that probably doesn't help one bit but....