Big Block Overheating, No Thermostat

[VAD Gold Rush]

Short Version,
Can you run a big block without a thermostat without problems?

Long Version,
I finally got to drive my 1974 Plymouth Scamp yesterday. It has a 400 swapped into it. Plenty of coolant, very minor leaks, but it got extremely hot in a short amount of time. The engine cranks super smoothly, so I doubt any head gasket problems. The engine has no thermostat in it currently. I pondered if this would be a problem, but didn't figure it would that big of a deal. After pegging the temp gauge, I'm now wondering if that is a huge problem. I notice there is a small hole, approximately 1/2" if I remember correctly, in the water pump housing that I wondered if it needs to be sealed off by the bottom of the thermostat. I know the Cleveland Ford has that problem. I'm I correct in my assumption, or am I way out in left field?

 

[Kendog 170]

The hole under the pump is so when your bearing goes it will leak out of the hole. Sounds like bad WP. Did you inspect the impellor when it was off? Is it old? Don't block hole.

 

[j_anderson]

Sounds a lot like what happened to mine when I put the rebuilt engine back in. During transport from Dyno to my garage, I put rubber plugs in all the openings of the engine. When I installed the engine, my dad put the lower hose on and didnt remove the plug from the water inlet on the water pump. He couldn't see it.

We found that and put it back together and still had a fast heat up and hot temps.


Took it back apart and found ANOTHER plug that I had put in the radiator inlet last winter when I removed it to pull the engine. I put that in there to keep junk out of there while it was all taken apart.
Removed that, put it all back together and its cooling like it's supposed to.

You don't have any blockages like I had do you?

 

[PROSTOCKTOM]

You need the restriction of a thermostat to actually slow the water down so it can cool.

I know guys that take the thermostats apart or put a plastic disc in place of a thermostat with different size holes in the plastic to adjust there water temperatures on race cars, but

you should never leave the restriction out.

Tom

 

[dano]

Likely a previous owner pulled the thermostat to fix an existing overheating condition. Get a 180 deg high flow, I think Milodon makes one.

Any coolant leak will compromise your cooling system. It works under pressure with a coolant water mix. Straight water is not recommended.

What are you using to measure temp? Dash gauge or aftermarket?

State of tune can cause overheating, too retarded and/or too lean can increase the engine temp. Do not overlook proper timing and the correct amount of fuel.

400, could this have a lean burn distributor?

 

[RustyRatRod]

Sounds like the radiator isn't doing its job.

 

[VAD Gold Rush]

Likely a previous owner pulled the thermostat to fix an existing overheating condition. Get a 180 deg high flow, I think Milodon makes one.

Any coolant leak will compromise your cooling system. It works under pressure with a coolant water mix. Straight water is not recommended.

What are you using to measure temp? Dash gauge or aftermarket?

State of tune can cause overheating, too retarded and/or too lean can increase the engine temp. Do not overlook proper timing and the correct amount of fuel.

400, could this have a lean burn distributor?

The engine swap was done before I got the car, but the rest of the setup is my own fault.
I know the engine is running lean due to a vacuum leak in the throttle shaft on the carburetor. I'm getting a new base plate soon.
The coolant leak I found was fixed, though I still need to put sealer on the header bolts.
The temp gauge is aftermarket. The car has none of the stock instruments or wiring left.
The distributor is a stock points style with limited advance set at 20* initial timing.
I have a thermostat coming to the parts store soon to see if it helps.

 

[VAD Gold Rush]

Sounds like the radiator isn't doing its job.

It's a brand new, 3 row core aluminum radiator.

 

[VAD Gold Rush]

You need the restriction of a thermostat to actually slow the water down so it can cool.

I know guys that take the thermostats apart or put a plastic disc in place of a thermostat with different size holes in the plastic to adjust there water temperatures on race cars, but

you should never leave the restriction out.

Tom

That's what I'd always heard, but the only time I had an engine without a thermostat was a low output 318 that was in my 1971 Plymouth Satellite when I first got it going. It never even showed on the gauge, but that was in early March 2018 when it was still cold out here. The hot 400 with the heat of Oklahoma summer might be a different story.

 

[RustyRatRod]

It's a brand new, 3 row core aluminum radiator.

Ok. Then by all means, we all know new and good always mean the same thing.

 

[VAD Gold Rush]

Sounds a lot like what happened to mine when I put the rebuilt engine back in. During transport from Dyno to my garage, I put rubber plugs in all the openings of the engine. When I installed the engine, my dad put the lower hose on and didnt remove the plug from the water inlet on the water pump. He couldn't see it.


View attachment 1716427844

We found that and put it back together and still had a fast heat up and hot temps.


Took it back apart and found ANOTHER plug that I had put in the radiator inlet last winter when I removed it to pull the engine. I put that in there to keep junk out of there while it was all taken apart.
Removed that, put it all back together and its cooling like it's supposed to.

View attachment 1716427845


You don't have any blockages like I had do you?

I just double checked, and the water pump is definitely moving coolant. That's not guaranteeing there's no internal blockage due to rust or corrosion, but it something.

 

[VAD Gold Rush]

Ok. Then by all means, we all know new and good always mean the same thing.

Fair point, I don't trust new parts either.

 

[VAD Gold Rush]

The hole under the pump is so when your bearing goes it will leak out of the hole. Sounds like bad WP. Did you inspect the impellor when it was off? Is it old? Don't block hole.

I'm not meaning the weep hole in the pump. I'm meaning the hole in the housing that's right underneath the thermostat.

 

[RustyRatRod]

I especially don't trust anything larger than a two row with either 1" or 1.25" tubes. When you start stacking rows in front of each other, they become an air dam and reduce air flow. Tell you what you need to do. Go to Harbor Freight and get you a 20 buck IR temp gun. Shoot the temp of the radiator at the top of the core and then at the bottom and see the difference. It should be a big difference between the two.

 

[RustyRatRod]

I'm not meaning the weep hole in the pump. I'm meaning the hole in the housing that's right underneath the thermostat.

View attachment 1716427890

That almost looks like some kinda restrictor. I'd pull the thermostat housing and investigate further.

 

[VAD Gold Rush]

I especially don't trust anything larger than a two row with either 1" or 1.25" tubes. When you start stacking rows in front of each other, they become an air dam and reduce air flow. Tell you what you need to do. Go to Harbor Freight and get you a 20 buck IR temp gun. Shoot the temp of the radiator at the top of the core and then at the bottom and see the difference. It should be a big difference between the two.

I'll invest in one of those today. I don't know why I didn't think of that.

That almost looks like some kinda restrictor. I'd pull the thermostat housing and investigate further.

I looked into it before I installed the housing that's on the car. It's just a hole going between the thermostat and water pump. I initially thought it's a bypass.

 

[RustyRatRod]

Looks like that's how it's made. Here is one on the E bodies site. It appears to be the same.

440 Water Pump Housing

440 Water Pump Housing Available for pick up / shipping out of southwestern Ohio $60.00 OBO OE, bead blasted, primed

www.forebodiesonly.com

 

[Uncle Bob]

Short Version,
Can you run a big block without a thermostat without problems?

Long Version,
I finally got to drive my 1974 Plymouth Scamp yesterday. It has a 400 swapped into it. Plenty of coolant, very minor leaks, but it got extremely hot in a short amount of time. The engine cranks super smoothly, so I doubt any head gasket problems. The engine has no thermostat in it currently. I pondered if this would be a problem, but didn't figure it would that big of a deal. After pegging the temp gauge, I'm now wondering if that is a huge problem. I notice there is a small hole, approximately 1/2" if I remember correctly, in the water pump housing that I wondered if it needs to be sealed off by the bottom of the thermostat. I know the Cleveland Ford has that problem. I'm I correct in my assumption, or am I way out in left field?

What fan does it have?

I had a 7 blade fixed fan, though it was good to go but the car was overheating like mad. Then I looked up the part number (200) and found it was a /6 part with only 1/2" of pitch. I replaced it with a 216 clutch fan with 2-1/2" of pitch. I can't say for sure because I changed that and the water pump pulley at the same time but I think that was the one thing I threw money at that fixed my overheating problem.

Factory fans have the part number stamped into the blades.

 

[dano]

The engine swap was done before I got the car, but the rest of the setup is my own fault.
I know the engine is running lean due to a vacuum leak in the throttle shaft on the carburetor. I'm getting a new base plate soon.
The coolant leak I found was fixed, though I still need to put sealer on the header bolts.
The temp gauge is aftermarket. The car has none of the stock instruments or wiring left.
The distributor is a stock points style with limited advance set at 20* initial timing.
I have a thermostat coming to the parts store soon to see if it helps.

Thanks for the update. All good things for everyone to know.

On the Distributor, 1974 should be electronic not points. Can you confirm?

Initial timing is not limited in the distributor, that is distributor advance. So is your total timing 20*? If stock cam that's a bit high.

What carburetor?

Fan? Electric, fixed, clutched? Size?

Are the pullies originally from the 400?

 

[VAD Gold Rush]

Thanks for the update. All good things for everyone to know.

On the Distributor, 1974 should be electronic not points. Can you confirm?

Initial timing is not limited in the distributor, that is distributor advance. So is your total timing 20*? If stock cam that's a bit high.

What carburetor?

Fan? Electric, fixed, clutched? Size?

Are the pullies originally from the 400?

The car is far from stock. It's a stock points distributor that I welded on to limit the advance. I plan to use an Accel dual point distributor, but I haven't gotten the correct adapter to use the RB distributor in the B block. The initial is at 20* at the moment.
It has an old MP purple cam, though I don't know which one yet. I haven't measured, just saw the purple on the camshaft.
The car is setup with an electric water pump drive. There's no fan on it yet, but the car got super hot within such a short amount of time, it was baffling. Five minutes of driving down the road and it was at 230.
I will be adding a fan off my buddy's 1976 Dodge Aspen 318 before the next drive.

 

[RustyRatRod]

An electric water pump is in no way form or fashion for use on the street. It's main function is for cooling a car down between rounds at the track. Just food for thought.

 

[dano]

The car is far from stock. It's a stock points distributor that I welded on to limit the advance. I plan to use an Accel dual point distributor, but I haven't gotten the correct adapter to use the RB distributor in the B block. The initial is at 20* at the moment.
It has an old MP purple cam, though I don't know which one yet. I haven't measured, just saw the purple on the camshaft.
The car is setup with an electric water pump drive. There's no fan on it yet, but the car got super hot within such a short amount of time, it was baffling. Five minutes of driving down the road and it was at 230.
I will be adding a fan off my buddy's 1976 Dodge Aspen 318 before the next drive.

Is it an all electric pump or a motor that turns the water pump pulley?

 

[VAD Gold Rush]

Is it an all electric pump or a motor that turns the water pump pulley?

Electric motor driving mechanical water pump.

 

[forphorty]

Electric motor driving mechanical water pump.

There's your problem.

 

[VAD Gold Rush]

I threw a thermostat in the car. It did the exact same thing, only I drove a shorter distance so it didn't get as hot. I'm going to fix the engine's poor running for now, then rob a water pump pulley off a 440 in the storage unit to see if that helps.