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I have a GM Performance 350 HO in my '80. I went to the Engine Specifications document for the recommended spark plugs. The paragraph above the Ignition System section says:
"Any small block engine, regardless of year, that uses Vortec heads, will require an external coolant bypass line from the intake
manifold to the 5/8" hose nipple on the water pump (passenger’s side). Suggested routing is from the 3/8 NPSF boss on intake
manifold to the water pump."
Uh, I don't have an external coolant bypass line as GM describes. The heater hose connects to the 5/8" hose nipple on the water pump (passenger’s side). I have an Edelbrock Performer RPM Air Gap intake, and all the coolant bosses are either used for sensors (2) or plugged.
Why do Vortec heads need an external coolant bypass line?
I have a plugged coolant boss on the intake I can use, but do I really need to replumb my water pump to add an external coolant bypass line?
It's required because older small blocks have an internal bypass in the block. There is a small passage on the passenger side below the bottom water pump bolt that goes through the block up to the deck surface. Then, there is a hole in the head surface into the coolant passage. This lets coolant continually circulate when the thermostat is closed. The Vortec does not have that hole/passageway so the external bypass is required. Remember, even with the thermostat closed you still want the coolant circulating in the block.
The typical bypass uses the hole on the top of the pump to connect a hose to the intake manifold below/before the thermostat.
Now, you can also use the heater circuit as the bypass as long as the coolant can always flow through the heater core.
So, on your Vortec you need one or the other. A heater that always flows or an external bypass.
It's required because older small blocks have an internal bypass in the block. There is a small passage on the passenger side below the bottom water pump bolt that goes through the block up to the deck surface. Then, there is a hole in the head surface into the coolant passage. This lets coolant continually circulate when the thermostat is closed. The Vortec does not have that hole/passageway so the external bypass is required. Remember, even with the thermostat closed you still want the coolant circulating in the block.
The typical bypass uses the hole on the top of the pump to connect a hose to the intake manifold below/before the thermostat.
Now, you can also use the heater circuit as the bypass as long as the coolant can always flow through the heater core.
So, on your Vortec you need one or the other. A heater that always flows or an external bypass.
Day um! I put in a shut-off valve in my heater hose a couple of years ago. I haven't had steady coolant flow through the heater circuit since then.
Both bosses near the left-front corner of my Performer RPM Air Gap intake are currently used, one for the FAST EZ EFI coolant temp sensor and the other for my temp gauge. There is another 3/8" boss near the left-rear corner that is currently plugged. The alternative would be to put a T in the heater hose.
I don't like the heater hose T alternative and the coolant temp above cylinder #7 will be good enough for a temperature gauge temp. I'm going that option unless, of course, someone has a better idea.
Last edited by MN80Vette; Aug 24, 2015 at 07:38 AM.
Thats interesting.....I've had vortecs on my car without the bypass for years and I've never noticed anything interesting going on. The vortecs are coming off this winter so i'm not going to worry about it.
I run vortec heads without a heater core connected or an external bypass. I was getting high temp spikes after driving 2 or 3 miles. I drilled 3 bypass holes in my 180 thermostat to function as a bypass and it was the easiest fix for me. Cured by temp spikes but engine takes 5 more miles or so to warm up. Only reason I drilled the holes was to work as a bypass.
I run vortec heads without a heater core connected or an external bypass. I was getting high temp spikes after driving 2 or 3 miles. I drilled 3 bypass holes in my 180 thermostat to function as a bypass and it was the easiest fix for me. Cured by temp spikes but engine takes 5 more miles or so to warm up. Only reason I drilled the holes was to work as a bypass.
I like this idea...it's simple. I assume the holes don't need to be very big, like 1/8" or so?
I haven't had any temperature spikes that I know of based on my temp gauge and ECU live data. Both those temps are taken at the front of the intake, so I don't think the reading reflect the temp in the engine, below the thermostat. Holes in the thermostat would allow a little coolant to circulate.
However, I will look into relocating my temp gauge sensor to the 3/8" holes near #7 and re-purpose the hole near the front of the intake for a bypass.
Mine are no more than 1/8" and I tried to get them equally spaced around the stat. I'm not one of the "gotta drill a hole in hole in your stat" people, but in this situation it solved my problem. Plus I live in south Georgia and I dont care if the car takes a little longer to warm up. In fact its kinda nice
I like this idea...it's simple. I assume the holes don't need to be very big, like 1/8" or so?
I haven't had any temperature spikes that I know of based on my temp gauge and ECU live data. Both those temps are taken at the front of the intake, so I don't think the reading reflect the temp in the engine, below the thermostat. Holes in the thermostat would allow a little coolant to circulate.
However, I will look into relocating my temp gauge sensor to the 3/8" holes near #7 and re-purpose the hole near the front of the intake for a bypass.
I installed the cts for my efi in the head reasoning being the ecm controls the fan and I want the ecm to turn the fan on when the head gets to operating temp (Aluminium heads) and not when the thermostat gets to desired temp. EFI also uses the coolant temp to modify the tune , it is also how newer cars with EFI also have the cts installed in the head.
I installed the cts for my efi in the head reasoning being the ecm controls the fan and I want the ecm to turn the fan on when the head gets to operating temp (Aluminium heads) and not when the thermostat gets to desired temp. EFI also uses the coolant temp to modify the tune , it is also how newer cars with EFI also have the cts installed in the head.
When you say you installed the cts "in the head", do you mean in the intake as close to the head as possible?
My cts is currently located in the front center of the intake. This location is technically below the thermostat, but the cts will measure the ct accurately only there is coolant flowing. Without the water pump moving coolant through this area, the ct is dependent on coolant convection in that area.
I seem to be having temperature-related issued with my ECU. I live in Minnesota, and high temps have been in the lower 60's the past few days preceded by temps in the mid-upper 80's.
How does the coolant flow in front vs. rear of the intake? I'm thinking that if the coolant flows from front (where the water pump and connections are) to the back (where the un-used coolant port is located), then the rear port should provide a higher reading than the front, and will provide a better reading for the ECU?
Is my logic correct? If not, please advise.
Thanks.
Hey Majoho, I have the same issue. I've gotten several different answers from GM Performance that just don't seem right. Can I ask which route you took and how it turned out? I am going nuts trying to figure this out.
When you say you installed the cts "in the head", do you mean in the intake as close to the head as possible?
My cts is currently located in the front center of the intake. This location is technically below the thermostat, but the cts will measure the ct accurately only there is coolant flowing. Without the water pump moving coolant through this area, the ct is dependent on coolant convection in that area.
I seem to be having temperature-related issued with my ECU. I live in Minnesota, and high temps have been in the lower 60's the past few days preceded by temps in the mid-upper 80's.
How does the coolant flow in front vs. rear of the intake? I'm thinking that if the coolant flows from front (where the water pump and connections are) to the back (where the un-used coolant port is located), then the rear port should provide a higher reading than the front, and will provide a better reading for the ECU?
Is my logic correct? If not, please advise.
Thanks.
Not sure how i missed this, no it is in the coolant port between the exhaust ports.
Since no one mentioned it yet.......Almost all thermostats for Chevy- especially the higher quality ones, have a small hole or opening that allows coolant to flow even when the thermostat is closed. On my 454 the water pump bypass is plugged with a pipe plug and the bypass port on the intake is used for an additional coolant temperature sensor for my electric radiator fan on-off function.
I know this thread is really old but its the best one that Iv found. First off my application is not a vet but it has to do with the same situation. I have a 94 1500 with a 383 stroker. The block is a 97 vortec and the heads are the cast iron vortec heads. When I bought the water pump I bought it for a 94. Well now I know that a vortec has an external coolant by pass not an internal. So my question is Do I need a vortec water pump? My heater hose goes into my Manifold right next to my T stat. I do not have a spot to plumb another hose. Both locations have sensors in them. My truck was running a little warm above 200°. So I took the cheap 195 t stat out, put a Edelbrock 180 and drilled a hole on the passenger side of the t stat. The Tstat already had a hole on the driver side from the factory. No my truck runs in the 180s. If i run a v tec h20 pump ill have to use a Tee into the heater core hose? Is this where I would put the Tee?
If I remember correctly, it's the block that has a passage drilled from the deck down towards the inlet ports on the block. There are two water inlet holes, the big one and a smaller one that intersects the drilled passage. you would just need to check if your water pump has the upper smaller outlet hole that lines up with the one on the block.
But if your truck is running at 180 now.....what are you worried about? Don't make it into something it isn't.
see here for the flowpath. I would just drill a couple of holes in the thermostat-- that's what I did with my vortec heads about 15 years ago. Not only does it deal with the vortec heads but also helps with filling and venting. Follow the link for more discussion.
If I remember correctly, it's the block that has a passage drilled from the deck down towards the inlet ports on the block. There are two water inlet holes, the big one and a smaller one that intersects the drilled passage. you would just need to check if your water pump has the upper smaller outlet hole that lines up with the one on the block.
But if your truck is running at 180 now.....what are you worried about? Don't make it into something it isn't.
Good deal. I didnt know if I had to do anything else to get the entire head cool.
see here for the flowpath. I would just drill a couple of holes in the thermostat-- that's what I did with my vortec heads about 15 years ago. Not only does it deal with the vortec heads but also helps with filling and venting. Follow the link for more discussion.
To complete the flow path, the gasket and head both also needs a hole that matches that hole on the deck and goes to the coolant passage. The Vortec heads do not have this hole, so after even putting them on the above block there will be no flow.
To complete the flow path, the gasket and head both also needs a hole that matches that hole on the deck and goes to the coolant passage. The Vortec heads do not have this hole, so after even putting them on the above block there will be no flow.
Excuse my ignorance but im totally confused. I know i originally stated my truck runs at 180 but today it went up to 210ish then shot back down. My block and heads are vortec. So if I get an edelbrock intake made for a 96 to 2002 vortec that has the coolant bypass Machine in the front of the intake and a vortec water pump i should be good to go?Right now i have a water pump meant to be on a 94 5.7 w no bypass fitting.
"External coolant bypass line" for Vortec heads?
