overheating question

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F-BIRD'88
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Re: overheating question

Post by F-BIRD'88 »

Short of simple locked out timing you need to create a idle/off idle timing control circuit that will trigger the ECU to add timing when at idle and small throttle openings
(throttle position sensor or switch.+ MAP sensor (vacuum sensor)
This can simulate the function of old school idle/off idle) "vacuum advance" but EFI ECU controlled.

Lack of spark timing at idle and of idle cruise (especially on cammed up engines) Makes slow late cumbustion that heats up the cylinder walls and combustion chambers.

Back in the day emissions era GM used this lame idle timing to make the smog motor run hotter to reduce ex emissions at idle.. Of course lame throttle responce was a result. GM also modified the water pump bypass to make the engine run hotter at idle..
The origional design had the bypass/heater hose going to the back of the intake near the diz not to the front near the thermostat. Moving the heater hose to available rear water ports on the intake corrects this.. The engine idles cooler.
The cooling system works better.
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Re: overheating question

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F-BIRD'88 wrote: Sat Apr 17, 2021 8:06 pm The origional design had the bypass/heater hose going to the back of the intake near the diz not to the front near the thermostat. Moving the heater hose to available rear water ports on the intake corrects this.. The engine idles cooler.
The cooling system works better.
I don't recall any SBC getting heater water from the rear of the intake, however some Oldsmobiles did.

If you want the most heat from your heater you get the water from right at the thermostat where it is hottest. Moving the heater hose to the rear saved xx inches of hose per car x millions of cars = $ xxx,xxx,xxx.xx
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Re: overheating question

Post by BillK »

Belgian1979 wrote: Sat Apr 17, 2021 6:06 pm 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 ...............

However, today I saw it happen again when heating the engine up to temp ...................
I guess I dont understand exactly what is happening ? Today when you saw "it happening" what temperature was it up to ? Did the fans turn on ?

I have never been a proponent of warming an engine up for more than a minute or so before driving. Only exception would be a true race car.

I guess my main point is if the fans keep the temperature under control then what more do you want ? Maybe worrying about nothing unless I don't understand the exact issue.
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Re: overheating question

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Tuner wrote: Sat Apr 17, 2021 8:30 pm
F-BIRD'88 wrote: Sat Apr 17, 2021 8:06 pm The origional design had the bypass/heater hose going to the back of the intake near the diz not to the front near the thermostat. Moving the heater hose to available rear water ports on the intake corrects this.. The engine idles cooler.
The cooling system works better.
I don't recall any SBC getting heater water from the rear of the intake, however some Oldsmobiles did.

If you want the most heat from your heater you get the water from right at the thermostat where it is hottest. Moving the heater hose to the rear saved xx inches of hose per car x millions of cars = $ xxx,xxx,xxx.xx
It wasn't about the heater. It was about cooling at idle.
The old pre 1965 sbc intakes had the heater port at the rear of the intake near the diz. They moved it to make the smog motors idle hotter.. Many aftermarket intakes have these rear water ports too. Connect the heater hose there (heater or not) the motor cools better. If when you do this on a 400 sbc no need to drill steam holes in the cylinder heads.
Better circulation.

Here is a pic of a 63-64 sbc Rochester fuel injection lower manifold.. There is a pipe plug in the rear water port but thats where the heater hose goes. If you delete the heater you still need the heater hose water loop.
https://www.picclickimg.com/d/l400/pict ... Intake.jpg
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Re: overheating question

Post by F-BIRD'88 »

On this old sbc intake the rear water port bosses are there but not drilled and tapped. Improved cooling if you finish the job.
https://i.ebayimg.com/images/g/~GoAAOSw ... s-l400.jpg
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Re: overheating question

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I agree with the comment that your pump may be more of higher rpm type, I think eddy's pumps are the same deal. One version has the vanes milled so they won't cavitate at higher rpm but reduces low rpm flow.

When's the last time you cleaned in front of the radiator or between if you have AC? I know both my C3 & C4 collect leaves there good.
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Re: overheating question

Post by Belgian1979 »

BillK wrote: Sat Apr 17, 2021 8:44 pm
Belgian1979 wrote: Sat Apr 17, 2021 6:06 pm 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 ...............

However, today I saw it happen again when heating the engine up to temp ...................
I guess I dont understand exactly what is happening ? Today when you saw "it happening" what temperature was it up to ? Did the fans turn on ?

I have never been a proponent of warming an engine up for more than a minute or so before driving. Only exception would be a true race car.

I guess my main point is if the fans keep the temperature under control then what more do you want ? Maybe worrying about nothing unless I don't understand the exact issue.
Fans come on at 197 and the next at 200°F. (195°F thermostat). It warms up nicely but seems to keep climbing. I would not make much of it but temps are only 50-55°F during the day at the moment, so I worry a bit that when it gets really warm it wouldn't be able to cope.

Will try a higher initial of 26° and see what it does.

As for the heater hose under the thermostat to the pump: this is what Stewart also recommended to aid with the warming up of the car and to be able to use a normal thermostat. Personally all drawing I've seen with this hose had it connected to below the thermostat.

(BTW: pump and heads are modified to take the coolant also to the area between the 2 exhaust ports on each bank (pump to bank)
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Re: overheating question

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BOOT wrote: Sun Apr 18, 2021 2:47 am I agree with the comment that your pump may be more of higher rpm type, I think eddy's pumps are the same deal. One version has the vanes milled so they won't cavitate at higher rpm but reduces low rpm flow.

When's the last time you cleaned in front of the radiator or between if you have AC? I know both my C3 & C4 collect leaves there good.
This area is clean. It also has the 78 type spoiler in the front which aides the cooling some.

About the pump: this was a bit my reasoning. So this pump wouldn't help with the low rpm cooling? I choose it because it is a high quality piece with good bearings, high volume and it had the provisions to drill for the hoses to the center cilinders. Didn't know they were milled so low rpm flow is reduced. At least it wasn't said they were doing that.
Originally Stewart said to use their Robert Shaw thermostat for the reason the pump didn't have the bypass hole, which I did, but in winter it did have difficulties to get up to temp at times. That's why, when going to EFI I used the bypass hose and a regular thermostat. Combined with it dropping the temps when increasing the rpm to about 1500 I was indeed thinking about an idle flow problem which might be solved with bypass holes in the thermostat. I believe the Shaw item has 3 of those 3/16" holes in the poppet.
I must add that the bypass hose was also recommended by Stewart to resolve the issue and it did a great job at getting the engine up to temp. The 6 AN was also their recommendation.
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Re: overheating question

Post by Geoff2 »

I do not think the pump is your problem, but you need to turn it quicker with a smaller pulley, 10-30%. More info on www.stewartcomponents.com

I have the Edel Victor #8810 pump on my Pontiac. This is a Chev pump that I adapted to work on the Pontiac engine. Many years ago now. My engine actually cools at idle. Also fitted smaller pump pulley. I don't think the Edel pump would be any better than your Stewart pump.

You should only drill the stat IF the pump itself does not bypass.
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Re: overheating question

Post by naukkis79 »

Belgian1979 wrote: Sun Apr 18, 2021 3:29 am Fans come on at 197 and the next at 200°F. (195°F thermostat). It warms up nicely but seems to keep climbing. I would not make much of it but temps are only 50-55°F during the day at the moment, so I worry a bit that when it gets really warm it wouldn't be able to cope.
Is there a reason to run at those temps? There will be all kind of cooling problems if trying to run engine too cold. For correct pressure cooling system needs much higher temperatures, at those lowly temperatures cooling liquid might boil in hot parts of engine making vapor locks.
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Re: overheating question

Post by Belgian1979 »

195°F is best compromise on an engine in terms of running temperature, wear and performance.

As for the pulley, yes that was something I have been thinking about as well, but seemingly I cannot go any smaller than what is already on the engine. (6.250").
Crank pulley is 7.677" outside circumference. From what I see this is already one of the biggest.
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Re: overheating question

Post by allencr267 »

Fan temp sensor location not in the radiator's outlet?
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Re: overheating question

Post by Belgian1979 »

The fan is actuated by the ecu based on coolant temps. The sensor is in the driver side head between n° 1 & 3.
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Re: overheating question

Post by jeff swisher »

195°F is best compromise on an engine in terms of running temperature, wear and performance.

I have heard that kind of stuff for decades.
Do not try to convince me that 195 is best.
My engines run better at 160 or less.
Only hit taken is in the MPG department.
I have a 1969 300HP 350 that has many heads cams in it and every time I take it apart there is Zero wear.
I have had it apart for a refresh 4 times and after 400,000 miles I quit doing it because there is no wear.

140-160 F is where it spent most of it's life.
No sludge no varnish , standard bore standard crank.
You are waiting until the engine is very heat soaked before you turn on the fans.

Turn them on earlier and boil the thermostat in a pan of water on the stove to see exactly when it begins to open and when it is fully open.

Every 195 thermostat I have cooked begins to open at 195 and is fully open by 205.

180 thermostats I have cooked begin to open at 180.
160 thermostats I have tested are usually fully open at 160.

I run a restrictor plate in place of a thermostat.
If my ride is too cold in the winter I block some of the radiator.
I drive many thousands of miles a year and do not need a thermostat failure.
After having a few failures that could have stranded me I began running restrictors and no more issues in over 30 years.

Cook the thermostat and bring in the fans sooner.
Check temps at different areas with a temp gun to make sure you are getting correct readings.
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Re: overheating question

Post by allencr267 »

It needs it at the radiator, its outlet.
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