[dataway]

Originally Posted by HWYSTR455

You have to remove a fender to do a heater core? Should be able to just remove the inner fenderwell if that's what needs to happen. The fan holds the outside case in place while you remove the inside case, no?


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To remove the underhood suitcase .... pretty much yes. The heater core is on the interior side HVAC case ... so should be all under dash work. Shouldn't need to remove the underhood stuff ... except the heater hoses ... which are no fun either.

[HWYSTR455]

Originally Posted by grivera

I thought all coolants sold today are safe with aluminum components- do you know which ones aren’t?

Yeah, there is still some that are not, but are specifically labeled so.

Now they make the 'green' antifreeze that's aluminum safe, so it can get confusing. Read the label is my motto.


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[NeighborsComplaint]

Originally Posted by dataway

I was making the first tentative shakedown tests on the freshly restored 68 GTO and I noticed some condensation showing up inside the windshield on the passenger side aligned with the defroster outlet.

I'm assuming a heater core leak. The vapor is not coming out of the defroster vent, it's sneaking past the defroster vent gap to the upper dash ... I know because it's only on the passenger side.

Heater core is original, it was in great shape, I vacuum tested it, but did not pressure test it. I think it's leaking from a tank ... if it was leaking from the fins it would fog the whole windshield when I turn on the defroster.

Engine cooling system holds pressure when hot for what seems to be the normal amount of time, so it must be a small leak.

I've resigned myself to the fact I'm probably going to have to pull off the inside HVAC box and replace it ... but I was also wondering ....

There are some respected voices on the forum that have high regard for stop leak products like "Barts" (?). Would that be an option? I have no real experience with them, a bit hesitant considering new engine, new recored (expensive) original radiator etc.

So far no moisture showing up on the carpet etc. Was thinking about trying to locate a place to drill a 1/8" weep hole in the bottom of the case to check for coolant standing in the bottom of the case.

What do you think?

Taste test the condensation first. Wipe it with your fingertip and touch it to your tongue. If it's sweet, it's antifreeze, if it's not it's condensation. Rinse your mouth, it won't poison you. I had good results with the Bar's Leaks G12BP Powder Radiator Stop Leak, not the syrup with the pellets.

[dataway]

I could smell an ever so slight aroma of anti-freeze .. and the condensation, while it didn't leave a stain on the glass ... did feel way more "slick" than just water.

I should have tasted it.

I took a very short drive today and saw it forming again ... I didn't wipe it away so I'll check and see if there is any residue on the glass. Seemed to be producing less and less condensate every time I fire it up ... does modern coolant have any "stop leak" capabilities (like the old Prestone stuff). I'm using the gold bottle Zerex right now.

[Ram Air IV Jack]

Originally Posted by Schurkey

Aluminum heater cores have been "a thing" for decades. GM put aluminum heater cores in the '88--~'98 GMT400 trucks. I don't doubt that they were in use--somewhere--long before that.

If the thing fits, there's no reason it wouldn't work just fine.

Not decades man!! I replaced a copper/brass core in a late 70's Olds Cutlass some time back. GM using inferior materials is not uncommon. Just because GM uses these materials, is no endorsement it will last. Case in point, I had an aluminum radiator replaced in my late model Cadillac recently. It was covered under warrantee, but I asked the mechanics how this could happen in a newer car. Their response was inferior aluminum radiators made overseas! Didn't use to see it this much with the copper/brass radiators. This echos what the radiator shop people told me. Enough said!!

[MUSLCAH]

By pass the heater core ....and see what yah get.

[Brentco]

I researched this a bit ago, and GM has a factory approved coolant sealing compound that the dealerships used for decades. Supposedly they even put it in the cooling systems of all new cars coming off the line for a while. It’s sold as Acdelco Cooling System Sealing Tabs. Should be 100% guaranteed safe, so it’s worth a try (especially given the PITA of replacing a heater core).

I’ve also used a more modern product, Bar’s Liquid Aluminum Stop Leak, and it was very effective.

[dataway]

MUSLCAH ... I sorted already did that ... I was running the car for quite some time with the core bypassed ... never saw any condensation. Only recently hooked up the lines to the core, and first time I get it up to temp good, that's when I saw the condensation.

It will be a pain, but a new copper/brass core is only $120 ... and I've got all winter to do the job ... so better safe and than sorry (hope I feel the same way on hour five on my back under the dash).

I was planning on draining the coolant anyway to get all the "new engine" garbage out of it. And I'll probably turn up an aluminum restrictor while I'm at it since I don't think the reproduction core has the crimped inlet tube.

[NeighborsComplaint]

I learned this lesson trying to save $10.00 of heater hose ... never twist off the heater core end of the heater hose. The nipples are easily tweaked and the "welds" break. Always cut them off. When reinstalling new, leave enough extra length to cut and reattach if needed.

[dataway]

I typically grease up the fitting and hose a bit for installation ... while it certainly makes installation easier I've always wondered if there was any side effects of the grease on the hose, coolant etc.

[dataway]

Well ... that was quite a pain in the butt. About three hours and I got the interior HVAC taken out. Had to remove the glove box, radio, ash tray bracket, kick panel and lower AC duct work. Four speed nuts on the firewall side, two bolts on the dash side.

Pressurized the core to 40 psi and it had a comical number of leaks ... probably 20 of them throughout the core where the fins met the tubes .... very surprised, the exterior looks outstanding, literally like new, inside must be a mess. And this core passed a vacuum test perfectly before ever having new coolant run through it ... just goes to show sitting on a shelf for 30 years didn't do it any good.

New copper/brass unit on the way. That's $120 I sure wish I spent months ago.

[tjs72lemans]

Ya looks can be deceiving. And sometimes the cheapness in us wants to put money into other areas we know need it. Then we find out we fooled ourselves. When you're done, you'll know what you have. Probably the last time you'll have to do that job.

[Tom Vaught]

Once you install the new heater core, add the 5/16 restrictor in the feed line to the
heater core to keep from having the new core leak.

Have posted on this MOD many many times.

Tom V.

[dataway]

Got the new core installed in the HVAC case (but not in the car yet) ... and a mighty nice piece of work it is ... absolutely identical to the OEM unit in every detail, would not be surprised at all if they were the OEM vendor back in the day. "Thermal Solutions Manufacturing" ... supplier to Ames by the way.

Tom ... I just turned up one with a 1/4" orifice that fits in the inlet tube of the core, with a chamfered inlet ... large enough, or should I take it out to 5/16? Not installed yet so I would just have to pop it in the lathe for a moment. I also still have the OEM spring thingie in the head port. Going to be TN car ... so hopefully won't need much heat.

[HWYSTR455]

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You may want to psi test it anyway, just to be safe.


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[Formulas]

If you do pressure test your new one i would NOT got to 40 psi that is excessive like more than double operating pressure you probably created more leaks with your old one at that test pressure

just go to radiator cap pressure or a touch over but not much

[HWYSTR455]

Agreed, 20-25 psi should be good enough, it will get stronger with a few heat cycles too.

In a bad overheat, it could exceed 40 psi, but doubt anyone would let it go that far before pulling over/shutdown.


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[grivera]

Originally Posted by Tom Vaught

Once you install the new heater core, add the 5/16 restrictor in the feed line to the
heater core to keep from having the new core leak.

Have posted on this MOD many many times.

Tom V.

Do you have a link to this MOD?

[mzbk2l]

Originally Posted by grivera

Do you have a link to this MOD?

Here are a couple:

https://forums.maxperformanceinc.com...33&postcount=7

https://forums.maxperformanceinc.com...07&postcount=2

Other useful information in those threads, too.

[dataway]

Haven't put coolant back in and tested the new core .. but I did make this restrictor. Slips into the core inlet and has a small step to keep it in place.