Heater box bypass?

[pd_55]

Question for the M10 gurus. I’m in the middle of my motor swap and didn’t have the correct coolant bypass tube or silicone lines to mate up to the heater entry and exit hoses. Rebuilt motor and going from downdraft to sidedraft EFI.

 

I’ve read about the heater bypass and some say ok and others not ok; leads to running hot. I’m in AZ, so a heater is more or less optional. I’m installing a couple 4” fans under the dash for air circulation and ECU cooling and lined the firewall with heat insulation, to avoid a hot footwell. But I am looking for input on if my DIY bypass (pics) will be ok and not lead to issues with the motor running hotter than normal. The hose is about 3.75” back from the head, so should clear the firewall. Thanks.

Edited May 12, 2022 by pd_55

[Mike Self]

Were it mine, I think I'd leave the heater in place in my TY 114 2002.  While your bypass will work, the heater is a designed piece of the cooling system--even the cars sold in Central America and the Middle East had heaters--AFAIK there was no "heater delete" option.  So it figures in the car's cooling system design.  

 

If you remove the entire heater box, it'll leave a big hole in the firewall that you'll have to make a patch to cover.  If you plan to leave the heater box in place and simply use the existing fan to move air into the passenger compartment, you'll get a lot better air flow by removing he heater core--and that requires removing the box and opening it up, then reassembling and reinstalling.  Not a particularly pleasant task, especially if you shatter the plastic heater box.    

 

Just my opinion

mike

[dlacey]

In this configuration there is a flow of water through the head and pump that never sees a chance to cool (either at the Rad or the heater matrix)...you are 'short circuiting' the radiator. It will run hot.

Either block this bypass completely ( same impact as original heater valve set to 'off') or put a restrictor inside your bypass pipe. I use a 3cm length of thick wall rubber pipe with a ~7mm hole stiffed inside the bypass pipe. That way there's a small flow to prevent airlocks, but the majority volume is forced to take the radiator(cooled) route.

[pd_55]

@Mike Self Appreciate that. Don't intend on removing or changing anything with the heater box. I wanted to keep it if I eventually wanted to replace the blower motor as it currently doesn't work. Or if I wanted to take it back to stock. The only reason for me entertaining the bypass was to avoid buying a straight coolant tube (mine has a 90 degree so it doesn't line up) and/or new silicone hoses. The set I cut up were from spares that I had. There's enough invested in everything else, so I guess I'm on a budget now. But, what I don't want to do is compromise cooling. This is a weekend, spirited driver, no track time expected. 

[TobyB]

Just block off both ports for now.

 

When the valve's off, that's pretty much what it does.

(the late valve leaves a small air bypass, the early does not)

 

It will be harder to bleed, but just take your time.

 

If you were going to take it out permanently, what I do is run

a loop with a small restrictor in it- it makes bleeding a lot easier,

and prevents air from being trapped in the back of the head initially.

But not worth it if you're going to eventually hook up the heater.

Just get the nose of the car up a bit, like on jack stands.

 

And I don't like silicone hoses, but that's a personal prejudice.

 

In Seattle and Portland temperatures, the heat leak of a bypassed

heater didn't overheat a race car.  The car I bought from Mike Roberts

came to me that way, and he'd raced it for several seasons...

 

t

thermorocket science

[pd_55]

@TobyB Thanks for the input. I actually didn’t realize there was no flow when the heater was off. I was thinking it was like a modern valve where the opened heater valve let the  coolant through through the core, but still kept it circulating when it was closed. I have a late model 74, but still looks like the valve and flow is either on or off. I have the hose material, so maybe I can redesign to keep the heater hooked up. And I guess I could turn the heat on to help cool the engine when it’s warm,  even though the blower doesn’t work.

[lawddf]

I used some brass plugs from Lowes in the ends of the heater hoses for several years including a day at the track with no issues. I made a simple plate to block off the hole from the heater box. I recently re-installed the heater box and everything works fine. 

[jgerock]

4 hours ago, pd_55 said:

@TobyB Thanks for the input. I actually didn’t realize there was no flow when the heater was off. I was thinking it was like a modern valve where the opened heater valve let the  coolant through through the core, but still kept it circulating when it was closed. I have a late model 74, but still looks like the valve and flow is either on or off. I have the hose material, so maybe I can redesign to keep the heater hooked up. And I guess I could turn the heat on to help cool the engine when it’s warm,  even though the blower doesn’t work.

Toby mentioned the later valve design. It has a channel cut into it to allow a little coolant and air to flow even thru a closed heater valve.  I suppose that design was incorporated to prevent stale coolant from sitting in (and clogging) the heater core. The all brass valve in my 73tii is like this- I’m not sure about the plastic spool version.

[jgerock]

I scanned this from an old Roundel.  And they say everything has already been done?