overheating question

[Belgian1979]

A question guy:

Like many know I own a 79 Corvette. These always had a tendency to easily overheat. Now, I have upgraded the rad in the sense the heaviest core is in it (still copper though) and a Stewart stage 3 pump. Seems to do a fine job when driving even in hot weather, but she climbs easily in temperature when at idle for some prolonged time. Fans seem to get it back under controlled (dual Spall like setup with staged turn on of the fans).

However, today I saw it happen again when heating the engine up to temp since it is standing still for quite some time, and contrary to my instinct I increased the rpm...the temps dropped. This seems like a sure sign it is lacking flow at idle (ca 1050 rpm)
So what is the route to tackle this? I was thinking about overdriving the waterpump, but it has the stock pulleys on it and the pump has a 6.250" pulley which seems to be about the smallest. Drilling the thermostat with some holes to get more flow?

PS: since neither the block nor the pump had the bypass holes I have a tube connecting the top of the pump to the inlet manifold right below the thermostat.

[chevyfreak]

I blank the bypass, even on my chevy inlines. And run a restrictor in thermostat bowl. Bit smaller mech fan and a electric in front on a thermoswitch for when stuck in traffic. Takes a bit longer to heat up but works. No true petrolhead/gearhead is gonna go hard on a cold engine.

You can always go bigger crank pulley to speed up waterpump. Or just to test , blank bypass and give a couple of holes in thermostat , or restrict the bypass, could be that the bypass is giving more heated coolant to waterpump.

Chevyfreak.

[Belgian1979]

I blank the bypass, even on my chevy inlines. And run a restrictor in thermostat bowl. Bit smaller mech fan and a electric in front on a thermoswitch for when stuck in traffic. Takes a bit longer to heat up but works. No true petrolhead/gearhead is gonna go hard on a cold engine.

You can always go bigger crank pulley to speed up waterpump. Or just to test , blank bypass and give a couple of holes in thermostat , or restrict the bypass, could be that the bypass is giving more heated coolant to waterpump.

Chevyfreak.

Leaving the termostat out and putting a restrictor in it is no good around here. We do get very cold weather (freezing) in winter so...

If the bypass would play such a big role, wouldn't it also have the problem when increasing the rpm?

[Walter R. Malik]

A question guy:

Like many know I own a 79 Corvette. These always had a tendency to easily overheat. Now, I have upgraded the rad in the sense the heaviest core is in it (still copper though) and a Stewart stage 3 pump. Seems to do a fine job when driving even in hot weather, but she climbs easily in temperature when at idle for some prolonged time. Fans seem to get it back under controlled (dual Spall like setup with staged turn on of the fans).

However, today I saw it happen again when heating the engine up to temp since it is standing still for quite some time, and contrary to my instinct I increased the rpm...the temps dropped. This seems like a sure sign it is lacking flow at idle (ca 1050 rpm)
So what is the route to tackle this? I was thinking about overdriving the waterpump, but it has the stock pulleys on it and the pump has a 6.250" pulley which seems to be about the smallest. Drilling the thermostat with some holes to get more flow?

PS: since neither the block nor the pump had the bypass holes I have a tube connecting the top of the pump to the inlet manifold right below the thermostat.

Keep the by-pass so, you don't blow-up the hearer core when cold.
Stewart pumps are great when they are turned at a higher RPM however, there is a company called "FlowKooler" whose pumps provide more block pressure and are the best water pumpers I have ever witnessed below 3,000 RPM with the less power loss above it.

[steve cowan]

can i ask how much ignition timing at idle ?

[Belgian1979]

18°

[mag2555]

What are you running for a intake manifold, as all too many Edelbrock ones have far smaller water inlets at the flange then what’s at the head.
The lower pump pressure at idle rpms can not over come this restriction !

The fact is that if your pump pressure at whatever given rpm is not higher then your average system pressure then how do you expect coolant to move thru the motor?

Though it’s a bit expensive you might find that Evans brand coolant has the added benefits to solve your issue all on its own!

[Belgian1979]

What are you running for a intake manifold, as all too many Edelbrock ones have far smaller water inlets at the flange then what’s at the head.
The lower pump pressure at idle rpms can not over come this restriction !

The fact is that if your pump pressure at whatever given rpm is not higher then your average system pressure then how do you expect coolant to move thru the motor?

Though it’s a bit expensive you might find that Evans brand coolant has the added benefits to solve your issue all on its own!

ITB manifold. The passages were not small as far as I can remember.
I run Valvoline coolant in it.

So the Stewart pump is to blame?

[Tuner]

A question guy:

Like many know I own a 79 Corvette. These always had a tendency to easily overheat. Now, I have upgraded the rad in the sense the heaviest core is in it (still copper though) and a Stewart stage 3 pump. Seems to do a fine job when driving even in hot weather, but she climbs easily in temperature when at idle for some prolonged time. Fans seem to get it back under controlled (dual Spall like setup with staged turn on of the fans).

However, today I saw it happen again when heating the engine up to temp since it is standing still for quite some time, and contrary to my instinct I increased the rpm...the temps dropped. This seems like a sure sign it is lacking flow at idle (ca 1050 rpm)
So what is the route to tackle this? I was thinking about overdriving the waterpump, but it has the stock pulleys on it and the pump has a 6.250" pulley which seems to be about the smallest. Drilling the thermostat with some holes to get more flow?

PS: since neither the block nor the pump had the bypass holes I have a tube connecting the top of the pump to the inlet manifold right below the thermostat.

Restrict the bypass to the pump so less water recirculates and more water goes through the radiator. Does anybody else recall that in some applications the bypass hose fittings have a small ID, 3/8" or 1/4" ?

The days are gone but, a pal who rebuilt water pumps made high flowing pumps by replacing the stamped sheet metal impellers with the old cast iron impellers that had curved blades. He would also use a profile transfer gauge to acquire the shape of the volute in the pump housing and cut the impeller in the lathe to that shape. Then, when he pressed the impeller shaft and bearing into the pump housing he would press it to contact with a piece of paper as a shim to set the clearance for minimum leakage, like is done in blueprinting a boat jet pump. A stock pump with the tin impeller would barely dribble water into the radiator at idle, his pump would shoot water clear across the shop if some idiot started the engine with the upper radiator hose disconnected. Howard Stewart and Edelbrock, etc, aftermarket pumps may approach this performance.

[BigBlockMopar]

And how many timing advance at the raised rpm-level?
I would try to add more timing at idle, like around 24 orso as a test.

[Belgian1979]

Would be around 24-26° at the higher rpm.

Bypass tube is a 6 AN tube, so it has a pretty small ID.

[Tuner]

In the wayback dayze when 283 and 327 SBCs all had hot manifold vacuum 100% of the time, if the vacuum advance quit working they would run hot.

[Belgian1979]

In the wayback dayze when 283 and 327 SBCs all had hot manifold vacuum 100% of the time, if the vacuum advance quit working they would run hot.

It is controlled by the ECU, so there's no vacuum advance unit.

[Tuner]

In the wayback dayze when 283 and 327 SBCs all had hot manifold vacuum 100% of the time, if the vacuum advance quit working they would run hot.

It is controlled by the ECU, so there's no vacuum advance unit.

I'm pretty sure we all understood that. The fact I was trying to convey is without the additional advance supplied by the archaic diaphragm and spring mechanism the engines would overheat at idle and in general driving such as at steady cruise on level ground.

[F-BIRD'88]

No vacuum advance and only 18 initial... Thats ½ your problem. Try 26 base initial.. With your big cam try locked timing 34-36 at idle. (The cammed up motor actually wants MORE AT IDLE). If your intake manifold has the extra water ports at the rear near the distributor connect the drivers side rear to the heater hose on the top of the water pump.
Good info on water pump impeller mods.