Cooling system Gurus please step inside

Gears & Crosses · Oct 5, 2009

I got a 1986 GT that wont build any cooling system pressure and will run hot if the A/C is running. I have pressure tested the system to 16 lbs and it will hold it. I have tested the rad cap too and it holds pressure as well. What would cause this problem? I have a Summit H/D alum radiator, Mr. Gasket hi flow 180 deg thermostat, H/D clutch fan, factory shroud, bottom hose with the wire inside. I do have the heater core bypassed (do to leakage) with a loop.

Your wisdom would be appreciated. Thanks,
Gears

BlownFiveLiter · Oct 5, 2009

Wow, that's a name I haven't seen around here in ages! Welcome back!

That's a tough one. It sounds like it could be air in the system somewhere, as you wouldn't build hydraulic pressure when a bubble compresses. Try giving it one good burp if you can. Toss the front end up nice and high on some stands, remove the cap, and fire it up until you come to operating temperature. Once the coolant starts flowing, start adding and squeezing the upper hose. I have a big ol' radiator funnel like this one that fits tightly inside the radiator fill and acts as a reservior, so I can watch the bubbles come out of the system:

View attachment 243441

Gears & Crosses · Oct 5, 2009

Thanks for welcoming me back StangGT. I've been trying to work on my cars rather than work on the computer. I will try bleeding the system tonight if possible.
Anyone else?

Gears

HISSIN50 · Oct 5, 2009

How hot does it run (per an aftermarket gauge or temperature measurement) with the AC on?

Does it run hotter at speed or while idling?

Gears & Crosses · Oct 6, 2009

Hey StangGT1995, where did you buy that funnel? I need one of those.

Hissin50: The car will run to the L on normal on the stock gauge. I wont let it go past that. It will run hot standing still or moving.

I didn't get time to bleed the car last night. Will try again tonight.

Thanks for all the replies!!!!!!!!!!
Gears

BlownFiveLiter · Oct 6, 2009

I grabbed that pic off Autozone's website (just hosted it elsewhere), so they should have one. Most all of the big-name stores should, as far as I know. I believe it's made specifically for the purpose of wedging into the radiator fill and holding coolant, until the level drops, or raises.

I hear ya on working on the cars. I need to spend less time working on this site and my own, and more on getting my car moving again.

Gears & Crosses · Oct 6, 2009

Thanks StangGT,I will look for one of those tonight!

I think Stangnet was one of the very first sites I ever joined. I have learned so much here. I really enjoy looking around the site, but I've don't have the time like I used too. With work, family, church, cars etc. I do not have the free time.

Thanks again,
Gears

Gears & Crosses · Oct 7, 2009

Ok guys, here's what I found. It appears that the stock type cap will not seal to the Summit radiator. The neck on this radiator is long. I got my pressure tester to seal while it was running and I built up 10-16psi while running. My problem is where do I find a cap that is longer?
Also, while setting at idle, with the A/C on, system pressured up, the Infared pyrometer was reading 220 degrees at its highest. My factory gauge was reading all the way past NORMAL but not in the red. That still sounds a little high to me. I was pointing it at the intake manifold right next to the factory sensor.

Help!
Gears

HISSIN50 · Oct 7, 2009

There are a lot of guys running that radiator and I have not read of them having an issue with the caps. I'd call or email Summit (I've emailed them about parts interchanging and differences in parts, and have been impressed with their replies).

I cant see how the filler neck length is important - as long as the overflow orifice is the same distance from the top of the open neck (as a stock rad) and the attachment flange you screw it onto is the same dimension as stock. Does your cap not seem to clamp down as tight as it does on a stock rad?

I'd get yourself a real gauge (even if just a 15 dollar parts store mech version that you use under the hood while doing diagnostics). If I had a spare, I'd mail it to ya.

ddonaca351 · Oct 7, 2009

Well I don't think it's related to your problem... but I saw you mention your hc is bypassed, so I thought I'd share;

I had a heating problem that I couldn't find (when I had my heater core bypassed it would cool fine while moving, but once at a stop/traffic it would slowly, but surely start to build heat, and build and build... ) anyhow, I finally cured it by putting a flow restrictor in the hc bypass.

Might be worth keeping in mind.

54deuce · Oct 8, 2009

I had to use a stant pressure releave cap the one with the red latch on my griffin and that seemed to seal better then the other caps. I had this problem years ago and the neck was too deep for a stock cap when you put it on it just turns in with no pressure against it. I told people about it and even called griffin and they acted like I was crazy. So hope this helps you, it worked for my car she now has pressure after a cruise. I never had a overheat it just never had pressure on the system.

Gears & Crosses · Oct 8, 2009

The problem I am having is the bottom "disc" of the cap is not touching the "inner neck" of the radiator. I hope you can understand my crude description. When you put the cap on, you don't feel the cap spring compress at all. The radiator pressure tester has a longer reach for that bottom disc and sealed the radiator the whole time while testing.

Thanks for the offer on the gauge. I will buy a Sun gauge today. You would put it in the front/drivers side of the intake manifold?

Thank you,
Gears

Gears & Crosses · Oct 8, 2009

ddonaca351 said:
Well I don't think it's related to your problem... but I saw you mention your hc is bypassed, so I thought I'd share;

I had a heating problem that I couldn't find (when I had my heater core bypassed it would cool fine while moving, but once at a stop/traffic it would slowly, but surely start to build heat, and build and build... ) anyhow, I finally cured it by putting a flow restrictor in the hc bypass.

Might be worth keeping in mind.

Thank you for saying this. Now that I have pressure in my system, I was hoping it would solve my problem. It helped but I still think I am running too hot for the mods I have. I kinda suspected the bypass is hurting me too. I have seen this mentioned only one other time. How did you restrict the flow???

Thank you for your help,
Gears

Gears & Crosses · Oct 8, 2009

Unfortunately 54Deuce, thats the same cap I have now.

HISSIN50 · Oct 8, 2009

Yep, use the stock temp sender location.

I see the issue now. I don't have any great ideas for you though. If the new rad is that off, Summit should be able to suggest a cap that will fit.

ddonaca351 · Oct 8, 2009

Gears & Crosses said:
How did you restrict the flow???

Thank you for your help,
Gears

Get two stainless hose niples the right size for the heater hose, turn them back to back (niple sides out) then put a stainless washer in between them (I think I used one for about a #10 or 1/4" maybe...) and tig weld it together.

Or you could use brass and just braze it, I guess...

You can probably buy premade flow restrictors from companies that make plumbing parts, but I used what I had around the garage.

54deuce · Oct 9, 2009

Gears & Crosses said:
The problem I am having is the bottom "disc" of the cap is not touching the "inner neck" of the radiator. I hope you can understand my crude description. When you put the cap on, you don't feel the cap spring compress at all. The radiator pressure tester has a longer reach for that bottom disc and sealed the radiator the whole time while testing.

Thanks for the offer on the gauge. I will buy a Sun gauge today. You would put it in the front/drivers side of the intake manifold?

Thank you,
Gears

Is the neck flange bent up if so you may have to tap that down alittle. As for the cap the best thing to do other then seeing if they would take it back and give you another one would be putting a hard rubber O-ring or donnut to space up and seal the cap. They would not take my griffin back it was in the car to long before I found out.

Gears & Crosses · Oct 9, 2009

ddonaca351 said:
Get two stainless hose niples the right size for the heater hose, turn them back to back (niple sides out) then put a stainless washer in between them (I think I used one for about a #10 or 1/4" maybe...) and tig weld it together.

Or you could use brass and just braze it, I guess...

You can probably buy premade flow restrictors from companies that make plumbing parts, but I used what I had around the garage.

Thanks for the tip!

I got in a hurry last night and I was able to press fit a brass reducer bushing into my bypass pipe. My bypass is made of two 90 degree 1/2" elbows joined together by a 1/2" close nipple. On one end of the elbow I have a 1/2" to (?") hose barb adaptor for the small heater hose. On the other end of the elbow I have a 1/2 X 2" threaded nipple for the bigger heater hose. I double clamp each side of the bypass pipe. The brass reducer is pressed into the 2" nipple. It is reduced to about a 1/4" hole now.

Gears

Gears & Crosses · Oct 9, 2009

54deuce said:
Is the neck flange bent up if so you may have to tap that down alittle. As for the cap the best thing to do other then seeing if they would take it back and give you another one would be putting a hard rubber O-ring or donnut to space up and seal the cap. They would not take my griffin back it was in the car to long before I found out.

No my flange isnt bent. It is a very stout piece. It looks like it was machined from billet. I've had mine in the car way too long also to return it also. I bought this radiator because it was supposed to be almost a drop in. The funny thing is I heard that the Griffin radiators needed the special cap, but didn't hear about Summit's. I bet their radiators have changed specs from time to time!

To others, I have emailed Summit two days ago and haven't heard a word from them yet.

Gears

Cobra912 · Oct 10, 2009

well it sounds like the problem I ran into but I solved it by replacing my crappy Mr. Gasket theromstat, mine was stuck

Cooling system Gurus please step inside

Gears & Crosses

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