My 86, with L67/4T65E-HD, has an annoying leak of hot air into the cabin no matter what I do with the hot/cold door. Since I deleted AC when I did the swap I cannot run my vent fan in the summer unless I feel like sweating my @@s off. Can I safely build a bypass circuit for my heater core without damaging anything? Btw, my heater core lines come off of the block at the stock location (Alt Bracket). Has anyone done this or have any suggestions? Thanks.
Make sure heat loop will flow when you bypass heater core. w/o that engine will have problems. See my Cave, Heater
------------------ Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should. (Jurassic Park)
The only thing I would worry about is if you have issues with the engine overheating. Its nice to be able to turn on your heater to help cool things if needed. There have been times on hot days I have blasted my heater to keep from overheating.
If you are getting hot air (that is actually being heated by the heater core) blown from your vents when the temp selector is set all the way to cold on the HVAC control panel, then you either have a problem inside the HVAC box up in the dash or your temp selector door cable has an issue at either end (at the HVAC box or at the HVAC control panel).
This is not to be confused with hot air (possibly from the radiator) being able to make it to the cowl area where outside air is drawn into the HVAC system. If air that has been heated by the radiator is making up to the cowl area and able to make it into the HVAC system from there, then bypassing the heater core coolant flow is not going to help your issue at all.
You really need to identify the cause of your problem. A properly working Fiero HVAC system will never allow air flow thru the heater core with the temp selector set all the way to cold. Thus, a heater core flow bypass valve should never be needed. And like Ogre said, installing one that could block heater circuit coolant flow entirely could cause problems (like blowing out a hose, line, or even the heater core itself).
-ryan
------------------ OVERKILL IS UNDERRATED Custom GM OBD1 & OBD2 Tuning | Engine Conversions & more | www.gmtuners.com
[This message has been edited by Darth Fiero (edited 08-13-2014).]
My truck as a shutoff valve to the heater core as OEM (that is how you control temp)....it was built in '73 and still has the original heater core.... so old coolant in the core shouldn't be a problem
When you use the "Check Fit" button on that page, it says this part will not fit your pontiac fiero .
I wonder if the left over stagnant water left in the heater core will cause it to corrode , rust out then leak ?
Those valves are for vacuum controlled HVAC cars, so it won't be easy to make that work on a Fiero. You'd need an electronically controlled valve instead.
The coolant left in the heater core when bypassed in the summer would be no worse than the coolant being left in the core in storage during winter.
The only thing I would worry about is if you have issues with the engine overheating. Its nice to be able to turn on your heater to help cool things if needed. There have been times on hot days I have blasted my heater to keep from overheating.
I agree, and I think you also have stagnant water just setting in the core and hoses not moving. Im not sure, but I think water still flows thru the system when you turn the heat off...it just dont get ducted to the interior.. It can cause faster corrosion in the core. If you still get some heat even when the heater is off, why not make some kind of block off plate over the duct outlets for summer.
The problem isn't letting coolant sit in the heater core and not having any circulation. You should be using a good mix of fresh anti-freeze anyway and this should be sufficient to keep any corrosion in check, even without being circulated. But like I said, that isn't the problem. What is the problem is blocking off the heater circuit flow. The 3800 has only a small coolant bypass circuit built into the factory alternator bracket to help keep excess water pump head pressure from building in the heater core circuit when the thermostat is closed. I have never seen a 3800 Series 2 or 3 used in a car with a heater hose cut-off valve. Blocking the heater hose coolant loop could create high head pressure to build within the engine if it is operated at high RPM when the thermostat is closed and this could cause problems.
Again, the bottom line here is you don't need a heater hose shut-off valve. A properly working Fiero HVAC system seals off the heater core when the temperature control is set to cold. If yours is still blowing hot air when it is all the way cold, then you have a problem causing that (which I have explained in my other post).
Again, the bottom line here is you don't need a heater hose shut-off valve. A properly working Fiero HVAC system seals off the heater core when the temperature control is set to cold. If yours is still blowing hot air when it is all the way cold, then you have a problem causing that (which I have explained in my other post).
A car that didnt come with AC will let some air pass by the heater core even in summer though will it not? My first Fiero did, and a few Fiero enthusiasts told me it was normal so I did put in a bypass hose under the hood, it worked well.
A car that didnt come with AC will let some air pass by the heater core even in summer though will it not? My first Fiero did, and a few Fiero enthusiasts told me it was normal so I did put in a bypass hose under the hood, it worked well.
I have never taken the HVAC box in a Fiero apart that was not factory equipped with A/C so I can't tell you if the heater core is supposed to be completely shut off from air flow when cold is selected at the HVAC control panel. I have to assume it would be in those non-A/C cars because any air flow being allowed thru the heater core will result in a warming of the air coming out of the vents. I think the OP has a problem with this HVAC system inside the car that is letting air get thru the heater core when he has his temp set to COLD on the HVAC control panel and that is his problem.
Originally posted by Darth Fiero: Again, the bottom line here is you don't need a heater hose shut-off valve. A properly working Fiero HVAC system seals off the heater core when the temperature control is set to cold. If yours is still blowing hot air when it is all the way cold, then you have a problem causing that (which I have explained in my other post).
(edit to make more sense)No Car w/ good or dead AC will do like you say... but hot intake air can act like heater control problems.
When parked and car gets allot of sun then intake air and box under windshield is hot and can take awhile to cool off even when local weather temp is cool.
This assumes front compartment doesn't "leak" and let hot radiator air get suck into the heater intake. OE front seals and spare tire wall controls air flow to both areas.
If max air (recirculate) door has problem then maybe you get hot air from cabin suck in, not fresh air. Missing seal that goes around heater core tubing can "leak" hot air from front compartment.
In all cases in this post, Bypassing heater itself likely won't help. Bypassing w/ wrong plumbing will cause engine problem in many engine, causing coolant leaks from over pressure hoses and seals, etc. Block pluming can even damage the WP or make WP belt problems. Can cut MPG some too.
[This message has been edited by theogre (edited 08-15-2014).]
This is what happened with my '86 GT, from This thread...
quote
Originally posted by Patrick:
Back in the summertime, my heater core started leaking. I didn't need the heater at the time, so while I was tracking down a new core, I bypassed the leaking heater core by disconnecting the two rubber hoses from the core and re-connecting them to each other. However, between the two hoses I used a fitting which had a very small passageway for the coolant to go through. When I got the new heater core, I flushed out my system and I was very surprised at that time to discover my thermostat looked much like it does in the picture below. I didn't understand at the time what the heck had happened to the thermostat, so I just bent it back into shape and re-installed it. Unknown to me until the cold snap here revealed a problem, the thermostat arms bent again from "normal" water pressure in the system (because the thermostat "arms" were now weak from being previously bent).
So in retrospect it's now easy to figure out what happened. The fitting I used to temporarily connect the two heater hoses to each other restricted the coolant flow way too much and this resulted in higher than normal coolant pressure pushing against the thermostat. The long thermostat "arms" therefore bent.
Just wanted to close the loop on this. I finally figured this out. I had to take part of my ducting apart to solve another problem and saw the problem. When I reassembled by ducting system I put the control cable on the wrong side of the clamp under the dash. As a result I shortened the stroke of the heater door making it remain open slightly when on cold. Dumb problem, easy solution. Thank you for al of your inputs.
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