1985 305 TPI, is set up with a 5/8 coolant hose that has a brass splitter with one line going to the throttle body and the other line going to the heater core. Is this the input for the heater or the heater return line?

 

That's feeds the heater core. Coolant flows out of the front of the intake manifold, up to the throttle body through the U-shaped hose, through the bottom of the throttle body, then out to the heater core.

The other, larger heater core nipple through the firewall with the ?-shaped hose is the exit back to the radiator.

 

I think both heater coolant lines were 5/8 on the 1985 and then changed to 5/8 and 3/4 from ‘86 onwards.

 

Appears that my set up is similar but the difference is that the return line from the throttle body does not go directly to the heater, but goes back to the engine block. The heater hose is a separate hose that comes off the brass splitter. The splitter has 3 hoses. One from the engine block which I assume is the water pump, and then splits into two separate hoses which feed the throttle body and directly routed to the heater core.
Picture attached.

i assume that the hose from this splitter to the heater is the input to the heater temp control valve and then to the core. This is what I am seeking verification as all the hoses on this year (1985) are 5/8 diam.


Hose at 12 o’clock from engine block Hose at 6 o’clock goes to throttle body Hose at 9 o’clock goes direct to heater

 

That's not a factory arrangement so you have whatever custom setup you have.

 

Like Komet said, that's nothing like a factory TPI set-up. And it really appears to complicate the project. Best to remove all of it and start fresh.

When you stated in your original post that it's a 1985 305 TPI, I assumed your car was a 3rdgen, but I see it's a vintage Corvette.

Regardless, as I said in my first post, the factory design is for the coolant to come out of the front of the TPI intake manifold where your 12:00 hose comes (out of the block, you said), and it should go straight up to a nipple on the front of the throttle body with the U-shaped hose pictured below. That's where coolant is supposed to ENTER throttle body.


The coolant is then supposed to flow along the underside of the throttle body and EXIT through the port on the side of the throttle body, where your 6:00 hose appears to be entering the throttle body. So the coolant should exit from there and go to the heater core.

Or you can delete the throttle body hoses altogether. A lot of people do; it's a common mod.

Here's a pic of the flow from the throttle body. 1985 didn't have the bypass valve(#5 in the picture below), so ignore that and its associated hoses and just send a hose straight back to the heater core from the front of the intake manifold.

 

The RHD conversion for the 58 corvette has sacrificed almost all originality although the finished car is aesthetically just as attractive as the original on the outside and cabin. Moving the heater to the other side of the firewall has also led to some innovative plumbing etc….
The much maligned 305TPI does very nicely in the conversion, and when the engine head needed replacing I fitted a 350 top end (Interchangeable with the 305) which gives slightly larger valves and a smaller combustion chamber (58cc I think rather than 64cc) which is a noticeable engine performance improvement.

Having got this far with fixing the heater core leak, I will go with your suggestion and remove the throttle body coolant lines. I’ve already blocked off the 9th injector as the climate here Down Under is nothing like an Alaskan winter.
The only comment regarding your description and illustration is that the return hose from heater doesn’t return to the radiator, instead is is back to the front of the engine block in a 5/8 nipple very close to the line out from the water pump. It appears to me that this set up simply loops the heater core into the main engine water system, with the small diversion for the throttle body via the custom modification brass splitter. I think I will just leave this set up as returning to the radiator would involve further work (retained the original corvette radiator without a line in fitting) and originality is not where I need to be.

thanks for your post reply

 

Thread a nipple into the port in the top of the water pump and connect the heater core's return hose to it. That's what that port in the pump is for in such an old school application.

 

Thank for everyone’s help.

 

Back to the well for some advice….
I am making the bypass modification, and reverting the plumbing to the normal setup. Yes, the u-shaped coolant hose comes from the intake manifold straight up to the throttle body. On the current setup there is another nipple exiting from the intake manifold, and this is connected to the non-factory plumbing that I am removing.
See picture.
I have 3questions:
To complete the bypass modification this additional manifold nipple is not needed. Is it just a case of removing this nipple and plugging the hole?
Any idea what thread and pitch size for the terminating plug?
Is it normal to have two coolant nipples on the front manifold, or is this another case of my weird custom setup?

 

In a warm climate I'd remove the coolant lines from the TB completely. There is no fuel atomizing in that area, no danger of freeze up, but the direct connection would sure heat up the incoming air - and I don't see the vacuum control valve on there.

 

It's another case of your weird set-up.

There are three coolant ports on the front of the intake manifold. One is for the nipple for the U-shaped hose to the throttle body. One is for the coolant temperature sensor. And one is for the cold start injector switch. Your second hose nipple is not correct. Is there an unplugged connector laying around that might reach that vicinity? If so, then it's likely for the cold start injector switch, which should go where your second hose is.

You said you're going to do the bypass, yet you said you would be reverting it back to the stock set-up, so that's a bit contradictory. The throttle body bypass consists of deleting the hoses to and from the throttle body, then using the nipple in the manifold that had the U-shaped hose on it to run a new hose straight to the heater core. Then you would leave the nipples on the bottom and side of the throttle body unused. Then a hose exiting the heater core can run straight to a nipple in the port on the top of the water pump(that's probably plugged). So... out from the manifold to the heater core. Then out from the heater core to the water pump.

As for the other two manifold ports, the coolant temp sensor you'll need, and that looks like it below the U-shaped hose in your picture. But the cold start injector switch and cold start injector(aka the "9th injector") can be deleted, providing the PROM is reprogrammed for such a modification, and it looks like it has been deleted, as that second hose is where the cold start switch should be. So if the PROM chip has been programmed to delete the cold start injector, then just plug that hole. If the engine fires up without hesitation, then it's probably been programmed out. But if the engine has trouble turning over, then it's probably because it needs the cold start switch and injector.

 

Your exactly correct, the cold start injector switch has been replaced with a coolant nipple, and the wiring loom connector is taped up and was poked in under the plenum at the front. I wondered what the additional plug was for.
Yes, the ECU is turned off for the cold start and the fuel injector removed and blanked off.
I stand corrected re reversion to factory set up. What I really meant was removal of the unnecessary custom plumbing and then the bypass modification exactly as you have set out.
I am now completely clear going forward, appreciate your help!

 

Thanks Tom3.
Definitely going to bypass the tb. No vacuum control valve on the current set up, What’s the benefit of this as I wasn’t planning to install this as I plan to simply install a new coolant line from the manifold intake to the heater core and a new re5un line o the top of the water pump.

 

The vacuum valve would keep the hot water out of the heater core and off the throttle body when not needed. Not sure if the always hot heater core would have the HVAC air flow diverted around it when the AC is on or not. But would be nice to get rid of the extra plumbing in the engine compartment for sure.

 

I think Tom is referring to the vacuum controlled diverter valve, which I called a bypass valve in post #6, where it's shown in the diagram I posted with an arrow as item #5. It wasn't on all model years, from what I've seen. It's helpful but not necessary, and 1985 didn't have one, so that's why I said to ignore it. Besides, your car will need an available vacuum line to make it function, which it probably doesn't have, so that's another reason I suggested to not worry about it. It's just another piece of unnecessary clutter. I removed mine years ago when I bypassed my heater core because the core was leaking.

 

Finished.
Following the bypass modification there are 3 less coolant hoses now, less clutter at the front end and less potential for leaks etc. Very happy to have taken your advice and also the help from tom3 + Komet.
Thanks.