Rblt 64 327-250 Overheating Issue - Help!

[Andrew P.]

So everything is new or rebuilt including a new (correct and dated) radiator from DeWitts. Temp Sender is reading 15deg low based on the gun readings.

Symptons (happens regardless of RPM or outside temp):
Starts fine...
Goes about 10-15 miles at what reads about 145 (actually about 160).
Climbs to 170/180 and will stay there about another 4-5 miles.
Then it gradually gains about a degree a minute and doesn't level out.

It's definately getting hot.

I switched the Thermostat. Same Result.

I switched the Fan Clutch. Same Result.

So I'll do the water-pump next but I think I may be missing something.

No water in the oil. Belts tight. A slight flat-spot in accelleration.
The rebuilder has been doing chevy 327's for many many years.

H E L P!!!!

Drew (Fallbrook)

[Timothy B.]

Re: Rblt 64 327-250 Overheating Issue - Help!

Andrew,

Expansion tank is half full with cold engine? When the engine is hot does it puke coolant? Did you check the temperature with your IR gun when it's very hot after it climbs to max.

Hard to believe it's a water pump problem but make sure the system is air tight and the hoses are snug so the pump is not sucking air. Where did you buy the waterpump?

New rebuild will run hot but should not overheat. Can you feel the hot radiator at the top and cooler at the bottom as that's where the engine pulls coolant.

[Doug F.]

Re: Rblt 64 327-250 Overheating Issue - Help!

is the system full of coolant ? when empty it will hold right at 4 gallons, bleed out the air through the heater hose at the intake, i've only seen 2 bad water pumps in my career, but it can happen

[Rich P.]

Re: Rblt 64 327-250 Overheating Issue - Help!

Did you plug any of the openings with paper when rebuilding the motor? Once in a while a stray opening gets overlooked and the masking material gets left and can impeed collant flow. I know it's a simple stupid thing but is just another possible cause.

Rich

[Jack H.]

Re: Rblt 64 327-250 Overheating Issue - Help!

Symptoms suggest minor leak(s) in the cooling system causing it NOT to hold pressure. The usual candidates are (1) rad cap and (2) hose joints at various clamping points (radiator to/from engine, heater hoses, head gaskets).

There's no reason to guess on this because most competent mechanics have a Stant pressure checker that can test/verify the rad cap with an adaptor that's part of the Stant kit as well as mounting the pressure checker directly onto the cooling system in lieu of the rad cap to test/verify the integrity of the on-car portion of the cooling system...

[Duke W.]

Re: Rblt 64 327-250 Overheating Issue - Help!

The rebuilder has been doing chevy 327's for many many years.


Drew (Fallbrook)

If I had a nickel for everytime I heard this one...

Was the engine rebuilt with all OE equivalent parts? What's the current bore dimension?

What is the spark advance map, and how does it compare to OE?

Duke

[Andrew P.]

Re: Rblt 64 327-250 Overheating Issue - Help!

Hi Tim,

Expansion tank is half full with cold engine?
-Yes

When the engine is hot does it puke coolant?
- Yes

Did you check the temperature with your IR gun when it's very hot after it climbs to max.
- I never allowed to "Max" but the gun says the Sender is reading 15 degrees colder than the gauge. It got to a reading of 220 once before I shut it off AND sit was puking out the overflow (new overflow and correct cap). Definately overheating.

Hard to believe it's a water pump problem but make sure the system is air tight and the hoses are snug so the pump is not sucking air.
Refilled and topped off. Very little air.

Where did you buy the waterpump?
Specialty rebuilder rebuilt a correctly dated housing.

New rebuild will run hot but should not overheat. Can you feel the hot radiator at the top and cooler at the bottom as that's where the engine pulls coolant.
Yep. Hotter and cooler.

??????

[Andrew P.]

Re: Rblt 64 327-250 Overheating Issue - Help!

is the system full of coolant ? when empty it will hold right at 4 gallons, bleed out the air through the heater hose at the intake, i've only seen 2 bad water pumps in my career, but it can happen

Hi Doug,

As full as I can get it. I'm topping it off through the upper radiator hose. Tricky but I'm getting almost all the air out.

Thanks

AP

[Andrew P.]

Re: Rblt 64 327-250 Overheating Issue - Help!

Did you plug any of the openings with paper when rebuilding the motor? Once in a while a stray opening gets overlooked and the masking material gets left and can impeed collant flow. I know it's a simple stupid thing but is just another possible cause.

Rich

Hi Rich,

I had it done by a professional rebuilder. I would HOPE so.

Drew

[Andrew P.]

Re: Rblt 64 327-250 Overheating Issue - Help!

Hi Jack,

No leaks or drips that we can find.

Andrew

[Andrew P.]

Re: Rblt 64 327-250 Overheating Issue - Help!

I know. I know.

The engine was done .030 over and the rebuilder does ONLY engine rebuilding and has done so for 30 years. Should I get the exact bore dimensions and materials used from him?

I have zero idea about the advance map but have a mechanic who could check it.

Drew

[William C.]

Re: Rblt 64 327-250 Overheating Issue - Help!

Have you verified that TDC actual (using a stop to find actual TDC) is the same as what is indicated by your damper/timing cover?

[Jack H.]

Re: Rblt 64 327-250 Overheating Issue - Help!

That's not what I said... Attach the Stant pressure checker to the system in lieu of a rad cap. Run the engine and watch the system pressure gauge on the pressure checker. It should climb to a level BELOW the rad cap's rated release level (should be 13 lbs) and STAY/MAINTAIN that pressure level.

If pressure continues to rise and crosses the 13 lb level, you've got leak(s) somewhere in the cooling system. Find and fix.

If pressure DOES stay and maintain BELOW the rad cap's release point. Now, attach the adaptor to the Stant pressure checker and exercise/verify the integrity of the rad cap REGARDLESS of how new it is...

[Timothy B.]

Re: Rblt 64 327-250 Overheating Issue - Help!

Andrew,

When you run the engine does the cooling system go under pressure. Can you feel pressure in the upper radiator hose? If it's a repro cap it may not be holding 15lb pressure and it will pop off sooner allowing coolant to overflow. You may want to check pressure relief on cap.

Just because the guage reads 15* lower at 160 does not mean it's reading 15* lower at 220*. These senders are all different so it's best to check thermostat housing temperature with IR gun if you have one. In archives there is a discussion on how the verify the dash guage calibration by using 60 ohms at the sender wire and the reading at the guage should be 230*. This test is simple and will tell you if the dash guage is in calibration. After that it's a matter of the resistance profile in the sender..

I don't see why you can't fill the system through the overflow tank, everytime you take the hose off you introduce air into the system.

How much timing are you running in the engine and does the vaccume advance work to spec for the 300hp engine.

[Andrew P.]

Re: Rblt 64 327-250 Overheating Issue - Help!

Andrew,

When you run the engine does the cooling system go under pressure. Can you feel pressure in the upper radiator hose? If it's a repro cap it may not be holding 15lb pressure and it will pop off sooner allowing coolant to overflow. You may want to check pressure relief on cap.

Pressure - Yes.

Just because the guage reads 15* lower at 160 does not mean it's reading 15* lower at 220*. These senders are all different so it's best to check thermostat housing temperature with IR gun if you have one.
I understand.

I ASSUME it's overheating because it started spitting waterout the overflow. and it "feels" hot.

In archives there is a discussion on how the verify the dash guage calibration by using 60 ohms at the sender wire and the reading at the guage should be 230*. This test is simple and will tell you if the dash guage is in calibration. After that it's a matter of the resistance profile in the sender..



I don't see why you can't fill the system through the overflow tank, everytime you take the hose off you introduce air into the system.

Because that's the high-spot in the system and that's where air ends up.


How much timing are you running in the engine and does the vaccume advance work to spec for the 300hp engine.

Factory Specs per my mechanic and yes the advance is working (250hp).

It overheats at idle also...

Strange.