Attn: Blower Gurus

[GT63]

Questions for you blower guys.

What psi of radiator cap are you using? I ask because every now and then, when I kill the motor after driving about 10 miles or so, it spits out about 8-12 oz of water from the overflow tank. It runs at about 185 when cruising down the road and each time it's puked water, it wasn't over 200. It doesn't do it all the time either. I'm pretty sure the cap is a 15 psi. At first I thought it was an air pocket, so I removed the cap after letting it warm up, then started it to see if it would burp and it never did. It's possible I just over filled the radiator, so I'll keep my eye on it.


Also is your temp sender in the back of manifold or is it up front? Which one is more accurate? I have mine in the rear.

I'm still working out the bugs, but so far she's running good with the Edelbrocks. I checked the #1 and #8 plugs after about 30 miles of driving and they were both a nice tannish brown color.

 

[Lee_in_KC]

I have a 15# cap and it has never puked. However, my motor runs very cool, like 160-170, which is weird because I have a 185 thermostat! At first, I thought I had a bad sender or gauge, but I recently changed out my gauges (and senders) from Dolphins to Autometers, and the water temp still shows 160-170. My sender is at the front of my manifold. I have the nice, two-core all aluminum radiator with a Spal fan that runs all the time. The only way I can see the temp staying so low is if the thermostat is stuck open or is mis-calibrated from the factory (or I forgot to put it in when I assembled the motor ).

One possibility with your motor is that the heads are running very hot and the coolant is flashing to steam when you shut off the motor and stop the circulation, thus over-pressurizing the system and causing it to puke. I would suggest you put your temp sender in one of the heads and see what you get.

You also might try filling the radiator with the front of the car raised, either on a jack or on a sloping driveway or something. That should help with any air in the system. You did drill your thermostat flange, didn't you?

 

[GT63]

Hey Lee, It sounds like yours does the same as mine. When I first start it, I watch the temp gauge. It will slowly climb to 210, then the thermostat opens and it will cool down to about 160 or 170. When I stop at a red light it might inch up to 180, but when I start moving it will drop back down. My fan runs as long as the key is on. I have a Walker Cobra radiator and the heads are aluminum Edelbrock Performer RPM heads with the larger 70cc chambers. The thermostat is one of those Reo-stat that stays open when it fails. It's a 185 degree thermostat and the radiator cap is a 15#. My brand new Patriot AHC coated headers aren't showing any fading due to high exhaust heat. They actually still look new even after about 60 miles with the new blower set-up. The #1 and #8 plugs looked right on the money with the tannish brown color. I'm using those new E3 plugs. If it weren't for this little purging of water , I'd say it was running great.

What's the drilling of the thermostat for? It wasn't mentioned in either of my Supercharger books.

 

[LumenAl]

Food for thought... when I first filled my up... it went a couple of weeks burping some water up here and there... then just like that, it found it's level and runs great and doesn't purge the water any more...

 

[Lee_in_KC]

Drilling the thermostat isn't blower related. It's a trick to reduce the chances of trapping air in the system. You drill a 1/8" hole in the flange of the 'stat far enough in from the outer edge so it isn't blocked by housing.

My temp never gets up to 185 ('stat temp). It stops rising in the 160-170 range and stays there. At the Nats it got up to about 180 during the parade to downtown. I don't know why we had to drive the whole way at 5mph!!!

I'm thinking my 'stat has got to be sticking (or failed) open.

 

[LumenAl]

...I don't know why we had to drive the whole way at 5mph!!!

Now Lee in KC... that's they call it a Parade vs. a cruse... drive, etc. Sure makes for an itchy right foot huh? :rofl:

 

[RPM]

Mine was doing the puke thing till I quit filling the rad back up every time it did it. It just need some room in it to expand I guess. I went to a 24 lb cap to try and stop it but it did not help it. I did put a puke can on it.

 

[blownt]

This is from Stewart Components. I drilled the last themostat I had but I run the middle size restrictor with no problems. I do not know how they can decrease coolant flow and inhibit cooling? They come is three different hole sizes..... Been using them for years with no problems.


Thermostats & Restrictors
We strongly recommend NEVER</B> using a restrictor: they decrease coolant flow and ultimately inhibit cooling.

For applications requiring a thermostat to keep the engine at operating temperature, we recommend using a Stewart/Robertshaw high flow thermostat. This thermostat does not restrict flow when open. The Stewart/ Robertshaw thermostat enhances the performance of the cooling system, using any style of water pump. However, the Stewart Stage 1 high-flow water pump may require this thermostat to operate properly, and Stewart Stage 2, 3, and 4 water pumps simply will NOT operate with a regular thermostat because these pumps have no internal bypasses.
Stewart further modifies its thermostat by machining three 3/16" bypass holes directly in the poppet valve, which allows some coolant to bypass the thermostat even when closed. This modification does result in the engine taking slightly longer to reach operating temperature in cold weather, but it allows the thermostat to function properly when using a high flow water pump at high engine RPM.

A common misconception is that if coolant flows too quickly through the system, that it will not have time to cool properly. However the cooling system is a closed loop, so if you are keeping the coolant in the radiator longer to allow it to cool, you are also allowing it to stay in the engine longer, which increases coolant temperatures. Coolant in the engine will actually boil away from critical heat areas within the cooling system if not forced through the cooling system at a sufficiently high velocity. This situation is a common cause of so-called "hot spots", which can lead to failures.</SPAN>

Years ago, cars used low pressure radiator caps with upright-style radiators. At high RPM, the water pump pressure would overcome the radiator cap's rating and force coolant out, resulting in an overheated engine. Many enthusiasts mistakenly believed that these situations were caused because the coolant was flowing through the radiator so quickly, that it did not have time to cool. Using restrictors or slowing water pump speed prevented the coolant from being forced out, and allowed the engine to run cooler. However, cars built in the past thirty years have used cross flow radiators that position the radiator cap on the low pressure (suction) side of the system. This type of system does not subject the radiator cap to pressure from the water pump, so it benefits from maximizing coolant flow, not restricting it.


and this is on radiator caps -


Tech Tip #2 - Radiator Caps

Radiator Caps
In a cooling system, a higher pressure equates to a higher boiling point for the coolant. Higher coolant pressures also transfer heat from the cylinder heads more efficiently. We recommend using a radiator cap with the highest pressure rating that the radiator is designed to accept. In general, performance radiators will accept 22-24 PSI, and professional racing radiators will accept a 29-31 PSI.

The coolant will typically only build to 16-18 PSI, due to expansion up to 200F. However, if the engine does overheat due to external factors, the pressure inside the cooling system could reach as high as 28 PSI. Once the radiator cap has opened and vented coolant, the engine will not cool down until it has been turned off. The radiator cap is basically a "safety valve", so always use the highest pressure radiator cap that the radiator will tolerate. If you are unsure of the pressure rating for your radiator, check with the manufacturer for the maximum recommended operating pressure.


Radiator Cap Location
The radiator cap should always be located at the highest point of the cooling system, and on the low pressure side (after the radiator core).Cross flow radiators mounted higher than the engine are ideal because the cap is on the tank that is connected to the water pump inlet. This configuration offers 3 advantages:

1.The cap is at the highest point of the system, allowing any air to migrate to the area just below the cap. In the event the cap vents due to excessive pressure, the air will escape first.2.This area has the lowest velocity within the system, allowing air to separate from coolant even at high engine RPM.3.The cap is located on the low pressure (suction) side of the system, so it is unaffected by the pressure generated by the water pump.
For cooling systems NOT using a cross flow radiator, mounted higher than the engine, you must use a surge tank. A surge tank is typically a 1 quart tank mounted at the highest point of the system, with the radiator cap on top. The bottom of the tank is connected to the inlet side of the water pump with a 1/2" or 3/4" line. A 1/4" to 3/8" "bleed" line from the side of the surge tank is connected to the highest point of the low pressure side of the radiator. The bleed line allows some circulation through the tank while the engine is running. The surge tank is also large enough to allow the air to separate as the coolant flows through it. Air in the system will then migrate to the area just below the radiator cap, again so that it will forced out first if system pressure exceeds the radiator cap's rating.

In street car applications, an upright radiator (top and bottom tanks, with the cap on the top tank) represents a compromise that will work, as long as the car is not operated at sustained high RPM, like those seen in racing.

Any aftermarket thermostat housing that mounts the radiator cap directly above the thermostat location, or that mount the radiator cap in the top coolant hose, are NOT recommended. Both of those housing styles are poorly designed, and will push coolant out of the cap at high RPM.


http://www.stewartcomponents.com/Tech_Tips.htm

 

[Photoman]

I have a 15# cap and it has never puked. However, my motor runs very cool, like 160-170, which is weird because I have a 185 thermostat!

The rating of the thermostat doesn't control the coolant temperature. It's just a valve that opens at a certain temperature.

 

[Photoman]

It will slowly climb to 210, then the thermostat opens and it will cool down to about 160 or 170.

You have air in the block.

 

[Photoman]

Mine was doing the puke thing till I quit filling the rad back up every time it did it. It just need some room in it to expand I guess.

Exactly. You want all the air in the radiator and the upper radiator hose. If you fill the system full of fluid (no air) when it is cool, it will puke when it heats up due to expansion.

 

[Photoman]

This is from Stewart Components. I drilled the last themostat I had but I run the middle size restrictor with no problems. I do not know how they can decrease coolant flow and inhibit cooling? They come is three different hole sizes..... Been using them for years with no problems.

The benefit to running a restrictor or a drilled thermostat is it keeps all the air in the upper radiator hose or radiator and out of the block.