Heat system questions

[Tom '74 911]

I know there is a lot of info on this already on the forum. I've done a lot of searches already - many of which lead to comments like "do a search, there's a lot of info on this already on the forum".



So. . . my car is a '74 w/a '77 2.7 engine. The exhaust is a (2) in/(1) out system - not sure how that affects things?? See attached photo above. The heater blower motor in the engine compartment doesn't seem to work, but I can still get some heat by just pulling up on the heater box lever by the ebrake lever - as long as I'm moving along at least. My first question is this: would I get more heat if I deleted the blower altogether and set up more direct routing like in this photo below. (sorry if that's your car - it is a perfect example of what I'd like to do to mine.)



I realize that's not a '77 2.7 engine, but the heater hose routing looks direct and very clean. Can I do that to my car? Will I need these parts from Thom aka widebody911? Also, what hose is shown in the photo above - or better yet, what is the best replacement hose to use? There seems to be a lot of info, just not a lot of concise info on this.



Finally, while I do get heat, under certain circumstances I also get some great smelling exhaust fumes. It happens before the engine is fully warmed up and also under hard accelleration. This seems to be fairly common, however is it an indication that my heat exchangers are starting to rust thru? I'd love an excuse to replace them w/some stainless ones, however that's a fairly expensive experiment, especially since I'm not sure I want to roll the dice by taking my existing ones off and breaking studs/nuts/bolts etc...

Sorry to beat an oft. asked question, but thanks for everyone's help,
Tom

[Jeff Alton]

The pieces from Thom are what you need. The hose looks like it is from aircraft spruce, not sure of there website. The factory stuff works just fine though. IF you smell exhuast throught the heater, your exchangers could be rusty....

Cheers

[Jubbie]

Tom,

The 74' came with the 'backdated' heater ducts that came from the front of the fan housing down to the heat exchangers. The fan came later (not sure when) to boost the heat flow to the cabin. Your 74' body may not have been wired up for the fan that your 77' engine came with. You may check around and see if you can get it working. It may be desirable in Idaho.




I have the 'backdate' on my 77 C3 engine and it works great here in Houston. Weak heat at idle, but will burn your toes off at 2000 rpm+. You should be able to find the parts from a 74' engine to do the backdating if you want. I think Widebody's parts are for backdating a 3.2 engine. Your 77 should take the 74 parts just fine.

I have fairly new SSi's and get a noticible change in smell when I hammer the gas, but it is not bad. You could go get one of thoes home carbon monoxide sensors to be sure.

[ianc]

My first question is this: would I get more heat if I deleted the blower altogether

You will get the most heat by replacing your existing heater blower motor. They are kind of expensive new, or you can find a used one, or adapt an inexpensive motor to fit the housing. See here:

The Wavey heater blower motor fix

Don't get me wrong; if you backdate, you will likely get better heat than you now have with a broken blower motor. However, if you backdate, you will really only get decent heat when the car is moving. Since the backdate relies on the main engine cooling fan to supply air over the heat exchangers, if you get stuck in traffic in the rain, you better have a towel handy to keep continually wiping down the windshield.

If that doesn't sound like fun, think about repairing\replacing the blower motor. I know your engine compartment won't be as clean, but with that solution, even at idle, you'll get decent heat.

HTH,

ianc

[JTL]

I did a trial run without the heater blower fan today. There wasn't close to decent heat even driving 80mph. It was pretty cool with temps in the 20s...

I may uninstall the fan and ducting for the summer for better engine cooling but the fan is a keeper for the drivable winter months.

jt
-84 targa

[ruf-porsche]

74 did not come with a blower motor in the back. Looks like someone updated the heater system when they installed the 77 engine.

[NoLift911]

Originally posted by JTL
I did a trial run without the heater blower fan today. There wasn't close to decent heat even driving 80mph. It was pretty cool with temps in the 20s...

I may uninstall the fan and ducting for the summer for better engine cooling but the fan is a keeper for the drivable winter months.

jt
-84 targa

What kind of heat do you have? Auto or manual? Were you sure the flapper boxes were all the way open? There is alot of heat coming from the fan with no heater blower - at 80 and you get no heat there is something wrong.

-Jeff

[Tom '74 911]

I finally got some parts to get this going. I would've loved to go w/the cool ones that Thom aka widebody911 makes and sells (sorry Thom!) but unfortunately I found some used metal ones and decided to save some $$. Now I have a fitting question. I removed the existing right side piece and immediately ran into a problem. There's something in the way of the buldge of the new piece. Please see photos below. The first shows the offending part circled, the second shows the new shroud piece - it won't fit.





What exactly is the part that's in the way? Can I just rotate the offending part counterclockwise so it's out of the way? It looks like it should rotate.

Thanks for the help,
Tom

[ianc]

That is the oil pressure sender. Someone has updated your motor with the Carrera chain tensioners (that's a good thing).

I don't think you'll be able to rotate it without mucking up the tensioner oil line, which is the thing you see coming out of the right side of the grayish green block (adapter).

You can either try to find an adapter that will let the sender lay horizontally, or you can try to bend the metal piece you bought to fit over the sender without damaging it. Couple shots with a ball peen hammer may do the trick. Rattle can it black; that looks horrible!

ianc

[wowzer911]

That isn't the correct piece for your 2.7, with the correct piece, the oil pressure sender location will not be an issue. The correct 74-77 OEM pieces will be plastic, not metal.

[Tom '74 911]

Wowzer -
So there's a plastic piece that fits there that allows me to still "backdate" the heat? I will do some more searching.

ianc -
I think horrible is a nice way of saying how it really looks! I'm test fitting the pieces before I spend any time buffing them out - in case they end up not fitting!

Thanks,
Tom

[wowzer911]

Yes, the bend radius is different. see pic. (not my engine)

[wowzer911]

You could make your part work, but you will need to rotate (angle) that pressure sending unit towards the rear.

[bigchillcar]

i second ianc..replace the heater blower motor. it ain't as pretty, but the blower would sure come in handy in the winter. also, check all your ducting for integrity..may have some holes/air leaks somewhere along all of those lengths of hose.
ryan

[Tom '74 911]

I just spoke to the P.O. - he said the blower motor should work. When they retrofitted the '77 engine to the '74 chassis, which didn't come w/a blower, they set it up so the blower either ran all the time, or never ran. They didn't connect it to a switch up front or the heater lever. In the summer, they just unplugged it in the engine compartment. He let me know where to go looking as far as getting it running again, so I think I'll give it a shot before I ditch it completely - it does get cold here in Idaho! Bummer cause I just pulled the complete assembly out last night - at least I know what's under there now!
Tom

[Brad01mc]

Hi!

I just took apart my heating system because I thought the motor was bad. Pull the connectors and test it with a 12V source before you give up on it.

So, It turns out that there are two little switches at the bottom of the heater flap levers that were not making solid contact.

I ended up taking the switch apart and cleaning the contacts until shiny. I also needed a new relay.

Works fine now.

Brad