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Stock LS routes water thought the heater core full time. I’m told that connecting the heater hoses from the LS pump to the C3 heater valve and heater core will cause the engine to overheat. This is because the C3 heater valve blocks the water flow returning to the pump when heat is not on inside the car.
I currently have the ICT heater core bypass hose installed on the LS water pump and therefore no heat.
I have the Holley Mid Mount that has 2 sets of heater hose ports. (Bottom and side of the pump) Would leaving the bypass hose installed, and connecting the other ports to the heater core and C3 heater valve work? Any other ideas to get the heater working in the car?
Last edited by TorchZ51; Nov 20, 2024 at 01:48 AM.
A heater bypass (U shape hose on pump) is what causes difficulty cooling because hot water is bypassing the thermostat and going into the engine all the time.
What you want is to block off the heater core outlets at the pump itself tap the heater core and plug them both.
Its not like an SBC. If you leave out the thermostat the engine recirculates hot water and overheats. That is what a U-shaped hose between the heater core ports causes also just not as fast
I've never heard of a engine over heating because the heater core was blocked off.
Where do you guys get this ****?
The LS thermostat is mounted backwards, and requires a hot signal on the cold side to open. It's more complicated than that, so I'd suggest you read up on it.
OP, you may get better answers with less snark if you post LS-specific questions in C5, C6, or on LS1Tech.com. I read up, and watched YouTube videos, and decided to drill a hole in my $100- LS water pump, rather than risk overheating.
Morning I agree with Bikespace on how the thermostat works. The way I solved the problem is I had a block made that went in the heater hoses with a 1/4in bypass hole drilled between the 2 lines. I have vintage air so I installed the bypass block before the shutoff valve.
The LS thermostat is mounted backwards, and requires a hot signal on the cold side to open. It's more complicated than that, so I'd suggest you read up on it.
OP, you may get better answers with less snark if you post LS-specific questions in C5, C6, or on LS1Tech.com. I read up, and watched YouTube videos, and decided to drill a hole in my $100- LS water pump, rather than risk overheating.
You are 100% correct on the LS thermostat operation. The Holley instructions clearly state not to block the heater hose ports and that a bypass is required to maintain flow. My thought is to use the ports already on the pump itself. Put the bypass on the Side ports maintain the flow. Lower ports connect to the C3 heater valve and core. Thoughts?
Another one of the issues that aren't an issue unless you install a LS engine. There are "plenty of pluses" and now "a few negatives" to installing an LS engine.
I am like you 4-vettes as this surprised me as I have had my heater core both connected and disconnected and there were no issues! I used to have a manual valve on the heater core supply line to shut off the HOT coolant from circulating through the dash. But then I couldn't use my heater core as an "auxiliary Radiator" when the engine got really warm....
I've had the heater ports blocked on my LS water pump since 2017 its been that way since at 600rwhp turbocharger daily driver over 50,000 miles and I can hold the water at 160*F if I want in Florida weather.
I'd like to see where it says in some holley instructions that they need to be kept open because I think its either a mis-print or incorrect and I will contact Holley over it
Although maybe they have provided a non-standard water pump? Or some aftermarket thermostat that interferes? Is this a kit? Like engine pulleys and thing? Can you provide part# for water pump I am intently curious
I've had the heater ports blocked on my LS water pump since 2017 its been that way since at 600rwhp turbocharger daily driver over 50,000 miles and I can hold the water at 160*F if I want in Florida weather.
I'd like to see where it says in some holley instructions that they need to be kept open because I think its either a mis-print or incorrect and I will contact Holley over it
Although maybe they have provided a non-standard water pump? Or some aftermarket thermostat that interferes? Is this a kit? Like engine pulleys and thing? Can you provide part# for water pump I am intently curious
I'll tell ya what guys, as reliable as my gen 1 Chevrolet Small Block V8 has been, I'll just continue to keep running it. And do my damndest to ignore posts like these.
Read up about it? Why?
where this guy explains that there are two styles of thermostats, a typical one and then a “bypass” one that has holes in the bottom and allows water to pass through. He explains that if you block off the water pump fittings you either have to tap and drill new ones in another location, or you have to use the “bypass” thermostat to keep the engine from over heating.
Anyone know if there’s any truth to this? It sounds logical and could be the reason why some of the guys in this thread claim they’ve been running blocked off heater hoses with no issues.
But at the same time, I find it hard to believe that in all the years this swap has been done, this is the only guy to discover this simple solution.
Last edited by rabinaba; Nov 21, 2024 at 10:54 AM.
I'll tell ya what guys, as reliable as my gen 1 Chevrolet Small Block V8 has been, I'll just continue to keep running it. And do my damndest to ignore posts like these.
Read up about it? Why?
I can't speak for all the other guys with LS swaps in their C3s, but for myself, it was well worthwhile reading up on upgrades. Now my 77 can cruise very comfortably as well as trounce 99% of Corvettes out there on the street or the track. And that includes C4s, C5s, C6s, C7s and C8s.
To be honest. I think whoever wrote the Holley instructions was just guessing and being cautious. In other words, I don't think even they knew.
I don't think the person who wrote the instructions designed the pump or understands how it works. I've found a couple mis-prints or typos in the holley instructions before so it wouldn't surprise me if they winged it.
It may be, that somebody decided to play it safe and do what people have been doing (wrong) for so many decades already. Because if you tell people to let the water flow, the worst thing that happens is the engine seems like it always wants to overheat and has difficulty cooling, but it will still 'work' and pump fluids around. If you notice this behavior then, thats probably the problem.
Waiting to hear back on this though. I don't know what "LT1 PUMP" means tbh. I opened a thread on holley site and if anybody wants to send them an email or take pics of the insides of this special pump so we can compare to LS1 pumps that would be great too
I can't speak for all the other guys with LS swaps in their C3s, but for myself, it was well worthwhile reading up on upgrades. Now my 77 can cruise very comfortably as well as trounce 99% of Corvettes out there on the street or the track. And that includes C4s, C5s, C6s, C7s and C8s.
Yep with a pos junkyard LM7 they gave me free rusty old 180k miles 5.3L I put in my car 2017 and make 600rwhp over 50,000 miles already daily driver I'm at 230,000 runs flawless no leaks no smoking all factory bottom end 25mpg 4l80e built myself. No machine shop no down time and the engine was free build thread in sig including tune file and transmission mods.
Cant do that with an free SBC just slap together high mileage 200,000miles+ 600rwhp gasoline daily driver haha dreamin!
To close the loop on this, it seems that @TorchZ51 is using the Holley Mid Mount pulley/accessory kit. The second set of heater hose holes is unique, AFAIK. All other LS engine water pump solutions require plugging and drilling new holes to avoid the C3s A-Arms (unless you get very lucky). Perhaps you can confirm that the kit uses truck spacing (-03) for the accessories?
Anyway, this thread came back to life, along with a solution of how to build that system for almost a reasonable price. The author of this video "saved" enough to buy a running LM7.
As for why doesn't @Kingtal0n's LM7 overheat if there isn't a hole in the water pump, perhaps there is a hole in the thermostat?
When I put my LM7 together (dry fit, not run yet), there was a one-way needle valve in the thermostat. I removed that, and drilled the hole out a bit bigger. There is a larger hole that I drilled in the water pump housing itself. I should try to get pictures sometime.
LS swap heat options
