Vortec Coolant Bypass - Can't you just drill a hole in the head?

[SirRobyn0]

That's what I'm trying to determine for sure. Why would GM specifically drill a bypass into a vortec block but not the head? If they did actually do something like that, what about all the people without a heater hose port on the radiator? How are they supposed to run a heater and a bypass hose from the water pump if there is only one port? Vortec headed engines are a super popular swap, where's all the people with a rigged up bypass hose and a heater hose T'd in? Do they just all have temperature swings and nobody complains about it? Why don't my own two engines have temperature swings?

Like I said, I've got so many questions now. It's just as well, I'm currently sitting in a hotel room 600 miles from home and nothing to do, at least now I have something to research.

I cannot comment on the vortec heads as I do not own one nor have I installed them on anything other than a factory block in a newer rig, but as I read this thread, I keep thinking about the Chrysler 2.2 and 2.5 4 cylinder engines from back in the 80's and early 90's. They had a terrible problem with temp swings on the gauge from the factory. The solution was to drill a 3/32 hole in the thermostat, to act as a bypass. This solved the problem. I have to think that perhaps the hole you like to drill in your thermostats is the reason you don't see swings. Whether or not that's good enough in the long run I have no idea, but I'm following this thread and am another person interested.

 

[K5ride]

I know I've seen crate engines on display with vortec heads and the bypass port in the block. The early 330 hp version for sure. I pulled the following pic from Summit, which I'm assuming is from GM's own advertising. Notice it has vortec heads and even appears to be a vortec block as well (plastic timing cover, fewer bolt holes) but it has the bypass port.

You must be registered for see images attach

The GM crate engines using vortec heads that have the block bypass are using the 638 block. This was originally used in the TBI engines. These blocks are roller cam ready and some even have a provision for the mechanical fuel pump. I'm building one now. The true "vortec" block is the 880 block and does not have any provisions in the block or water pump for a bypass. They both use the same alloy and are equally as strong. The 880 bore is slightly shorter so most people that build a 383 use the 638 block so there is extra meat at the bottom of the bore.

 

[bucket]

The GM crate engines using vortec heads that have the block bypass are using the 638 block. This was originally used in the TBI engines. These blocks are roller cam ready and some even have a provision for the mechanical fuel pump. I'm building one now. The true "vortec" block is the 880 block and does not have any provisions in the block or water pump for a bypass. They both use the same alloy and are equally as strong. The 880 bore is slightly shorter so most people that build a 383 use the 638 block so there is extra meat at the bottom of the bore.

I know about the TBI blocks with roller cams and some have the fuel pump boss. The picture I posted is in fact a vortec block, the timing cover gives it away. Upon more research, the original equipment vortec blocks of course do not have the bypass, but replacement blocks even of the same casting number often have the bypass port and a functional fuel pump boss as well. I don't know how that is supposed to work for a stock replacement as the vortec water pump does not cover the bypass hole. There may be GM instructions to plug that hole and I haven't found it yet.

But as for the whole bypass issue, opinions are all over the place. Some people insist they are fine with no bypass. Some people insist the heater circuit, with no shut-off, does a fine job as a bypass. Some people insist that a couple small holes in the thermostat does a fine job. Some people insist than a dedicated bypass hose is required.

All methods have their advantages regarding looks, cost, packaging, etc. If you come up with a nice clean and tidy way to run a dedicated bypass, I'd like to see it.

One other tidbit that came up often in discussions. If you can get away with just a couple holes in the thermostat, you will be using your cooling system at full efficiency when the thermostat is open. A dedicated bypass will always let coolant bypass the radiator. Which is why GM went away from the in-block bypass. The external bypass used on the factory vortec intake is plumbed into the bottom of the thermostat opening. The thermostat used is a modern bypass type, which closes off the bypass hose when the thermostat is open.

 

[DoubleDingo]

On my '81 I use the heater hose as the bypass to the radiator, as it is always flowing coolant from the engine through the heater core to the radiator. Temps don't fluctuate at all. If I ever decide to tap the GM Performance intake for the bypass, it will then get the official bypass from the intake to the water pump. On mine, I have run it in triple digit temperatures on the open road, gauge stays about 1/4 up from "C". Sitting idling in In-n-Out drive thru, I use them as the example of idling because it always takes a long time here, and still a steady temp gauge. And no holes are drilled in the thermostat, just a stock thermostat for an '81 C20.

 

[77 K20]

Why not just use the lower, forward facing port for the temp sensor and the one next to the thermostat for the bypass?

From what I can remember (hey- it was back in 2014) the ports were different size. The forward facing one was too small for the temp sensor they sent me.

 

[77 K20]

Did the vortec heads make a big difference? Is it worth all the $$? Would you do it again? I've already purchased everything but just wondering if regular gen 1 aftermarket heads would do the same without the bypass headache and expense of the new intake manifold.

I bought a whole entire crate engine from GM (HT383) after my 400 started drinking oil after putting new heads on it. I wanted something with a roller camshaft after I found my old 400 had some lobes flattened when I bought it.

I did a TON of research and thought I made the best decision in the world to get that engine. And I was very happy for a month or two.. then fall and winter hit. Engine ran like crap. All my reading was from people who live in warm climates and they praise vortec heads and that GM performance intake. They suck in cold weather.

Vortec heads were meant for a multi port fuel injection system. Thus there is no heat crossover tube below the carb/tbi. With multi port you want the intake as cold as possible. Once winter hits fuel from a carb/tbi cannot stay suspended when it makes a 90 degree turn- and the fuel drops out of the air and puddles in the intake manifold. Intake manifolds usually have a waffle pattern or a bunch of "speed bumps" to help the fuel break away from the intake and become airborn again. The GM performance intake manifold is 100% smooth on the bottom.

So I bought an Edelbrock 7116 manifold. Has the waffle pattern. Has a heat crossover tube. I couldn't figure how to use exhaust, so instead that became my coolant bypass. In my case I want/need coolant to heat up fast. Going from the water pump thru the block and under the intake avoids being cooled off by the radiator and actually heats up the intake pretty fast (just a few minutes). Without it I could run 14 minutes on the highway and when I stopped the engine would sputter as the intake was icy cold. Unfortunately the casting was very porous. I was losing a lot of coolant. After I shut the truck off coolant would seep thru the intake and start puddling under my tbi. Edelbrock refused to believe me. I had pictures. So I bought a SECOND intake manifold maybe 6 months later. SAME THING! At that point I was so pissed I just dumped one or two of those tubes of alumniseal in the radiator and dropped from my 16? lb radiator cap to something like a 10 lb. Problem "solved".

Ultimately I need to get a multi port aftermarket fuel injection system. That would solve my cold weather issue and my Edelbrock TBI doesn't like it when it gets above 80 degrees either. Starts surging. (I have awesome luck, huh?)

So in my case I kinda wish I would have just put in a 6.0L LS engine... but in 45-75 degree temps it runs great! Lots of power. I don't have to work about zinc content in the oil.

Since you are a California guy then I doubt you will get -20 degree weather.


And I truly do not know why there is so much conflicting info out there about the coolant bypass. Some say they have run for years without one and it is fine. Others have issues. For me the temperature fluctuations only really showed up at highway speeds- maybe not many run 3,000-3,300 RPM on the highway? I also have a 4 core radiator from the 400/454 so I have tons of extra cooling capacity. In winter I even tried blocking off the radiator to help heat it up. Doesn't do any good with a mechanical fan and there is so much air coming in from behind the headlights and below the bumper anyway.

I've read the thermostat drilling trick works well- they said 2-3 small holes are best. But that adds time to the warmup of the engine. For me that was a big issue. Warmer climates probably not.

 

[Allan Abley]

I have had same issue. Have not tried the small holes but what is a small hole? 1/16th, 1/8th? What size hole are u drilling in the thermostat?

 

[bucket]

I have had same issue. Have not tried the small holes but what is a small hole? 1/16th, 1/8th? What size hole are u drilling in the thermostat?

If it's something I drive a lot in cold weather, I drill a single 1/8" hole. If it's generally something I drive in warm weather, I'll drill two holes.

I've heard other people talk about drilling bigger holes like 3/16", but at that point, you may as well not even run a thermostat, imho. That's just too much unregulated flow to the radiator.

 

[Frankenchevy]

I just ran the hose from water pump to intake. Pretty basic. Not really easy to see, but I guess that’s a good thing…

You must be registered for see images attach

 

[bucket]

I just ran the hose from water pump to intake. Pretty basic. Not really easy to see, but I guess that’s a good thing…

You must be registered for see images attach

You are running a vortec water pump aren't you?

You've been a little scarce around here lately, compared to normal. Everything going good?

 

[Frankenchevy]

You are running a vortec water pump aren't you?

You've been a little scarce around here lately, compared to normal. Everything going good?

Yes sir, staying busy. Essentially working two jobs until I wrap the work on the books for my contracting business.

Yes Vortec water pump. Thought it’d keep it simple.

 

[K5ride]

I know about the TBI blocks with roller cams and some have the fuel pump boss. The picture I posted is in fact a vortec block, the timing cover gives it away. Upon more research, the original equipment vortec blocks of course do not have the bypass, but replacement blocks even of the same casting number often have the bypass port and a functional fuel pump boss as well. I don't know how that is supposed to work for a stock replacement as the vortec water pump does not cover the bypass hole. There may be GM instructions to plug that hole and I haven't found it yet.

But as for the whole bypass issue, opinions are all over the place. Some people insist they are fine with no bypass. Some people insist the heater circuit, with no shut-off, does a fine job as a bypass. Some people insist that a couple small holes in the thermostat does a fine job. Some people insist than a dedicated bypass hose is required.

All methods have their advantages regarding looks, cost, packaging, etc. If you come up with a nice clean and tidy way to run a dedicated bypass, I'd like to see it.

One other tidbit that came up often in discussions. If you can get away with just a couple holes in the thermostat, you will be using your cooling system at full efficiency when the thermostat is open. A dedicated bypass will always let coolant bypass the radiator. Which is why GM went away from the in-block bypass. The external bypass used on the factory vortec intake is plumbed into the bottom of the thermostat opening. The thermostat used is a modern bypass type, which closes off the bypass hose when the thermostat is open.

You are correct on the 880 blocks. I knew there were some differences but after I read your post, I did some more research. The 880 block I'm building for another project is the late model 880. It's missing some timing cover bolt holes, no coolant bypass and no fuel pump provision. It appears there were 3 different styles of the 880 block. Some have the timing cover holes tapped / threaded, some have the coolant bypass, some have the mechanical fuel pump provision and some have all three. It appears from what I'm reading online is that the heavy duty trucks got the 1st gen 880 with all these items. I'm sure there are others as the years progressed. It's making me rethink my 880 build. I'm not into it for too much $$ yet and may look for a better 880 foundation to start with. Thanks for your correction, I always enjoy learning more.

 

[bucket]

You are correct on the 880 blocks. I knew there were some differences but after I read your post, I did some more research. The 880 block I'm building for another project is the late model 880. It's missing some timing cover bolt holes, no coolant bypass and no fuel pump provision. It appears there were 3 different styles of the 880 block. Some have the timing cover holes tapped / threaded, some have the coolant bypass, some have the mechanical fuel pump provision and some have all three. It appears from what I'm reading online is that the heavy duty trucks got the 1st gen 880 with all these items. I'm sure there are others as the years progressed. It's making me rethink my 880 build. I'm not into it for too much $$ yet and may look for a better 880 foundation to start with. Thanks for your correction, I always enjoy learning more.

Imho, no matter the variance, they are a good block to build from. What's not to like about a 1-piece rear main, factory roller cam, late model machining tolerances and the ease of running SFI?

 

[Raider L]

@K5ride,

I've read about this mod and it is very successful. Have at it. And, yeah, I'm like you why doesn't the maker say, "just drill hole here" . I think it's because of all the different engines these heads fit, some have a place to do it some don't, so the easiest thing is to run the hose. But in your case you can drill the hole, then do it. and yeah, you use the gasket as the template.