[Authentic-242]

Another cooling/overheating problem...I know, I know, I've searched , but can't find my problem. Here are the facts (71 GTO, 400 CID, 4BBL, 1969 #62 heads):
1. Last fall, drained coolant (didn't open block drains), new lower rad hose (with spring), new upper rad hose, new 160deg thermostat (pretested in kitchen - opened fully by 170deg - old 160deg in motor was stuck wide open, car always ran too cool), new Zerex green coolant 50/50 mix with distilled water and hydrometer tested at -34deg protection after circulating in motor). Before this activity, no overheating or other issues. In hindsight, I did a big no, no during coolant drain - I blew compressed air into upper rad hose to drive out extra coolant from bottom hose, which got out another 1/2gal., but i think I trapped extra air in the engine interior. Refilled coolant till just below thermostat (to remove as much air as possible), installed thermostat and housing, connected hose, completed filling.
2. Left rad cap off, ran motor to burp system, let run till coolant started coming out rad opening, capped and test drove car.
3. During test drive, water temp gauge would go spastic, knowing coolant couldn't change temp that quick, I suspected trapped air (steam) was the cause and went home.
4. Shut off car, lots of loud banging from cooling system after engine was off, temp gauge spiking above 230deg (I think called air cavitation - expanding and contracting air pockets in engine).
5. Bought coolant funnel that goes in rad opening, reburped, got more air bubbles, but when engine shuts off, big burp forces a mess of coolant out funnel top (something about water pump suction stopping?)
6. For a few days, perform multiple funnel burping, fluid retopping (I know leave about 3" below top), still loud banging when shutting off, erratic temp gauge, some dieseling when shutting off (must be hot!).
7. Worried about damaged head gasket, cracked head from hot engine. Pull all plugs - no coolant or wetness, no milky residue under oil fill cap or dipstick, no oil film in coolant. No leaks on ground or around engine showing air entry point. Perform engine compression check (cold engine), looked reasonable all cylinders within 15%. Pressure tested cooling system to 16lbs with all plugs out, no leak down after 1/2 hr time. Pressure tested cooling system with engine running. Ran up to say 11lbs pressure as engine warmed up, no spiking or erratic pressure readings. These tests gave me some confidence that I wasn't introducing combustion gases into the cooling system internally. The next step would be a hydrocarbon sniff test of the cooling system for fuel traces, but I haven't gone to a repair garage yet. No white smoke or high levels of water from exhaust pipes when running. Bought new 15lb rad cap.
8. Drained coolant down, pulled thermostat, drilled small hole in body to let air bypass thermostat during refill, refill and reburp system.
9. Stored car for winter, took out for a drive yesterday. Predrive inspection, coolant level 3" down from cap - check. Drove for a while just fine temp gauge stayed at 172-175 steady as a rock for about 25 miles around town not above 45mph. Came to stop light, the damn temp gauge started bouncing all around again, as I left light, quickly came right back to 175 and stayed there until next light, were it did the same thing again. Drove car home ( as long as I stayed moving the temp gauge was solid at 175).
10. Shut off car in driveway, no dieseling at all, but the damn banging was back for about 30 seconds and the damn temp gauge went to 250deg in about 10sec when it was fine at 175 moments before. Let cool, started it 1hr later when gauge was at 190deg, dropped right down to 170deg and put car in garage. Motor seemed to run fine, no noises, funny smells, good power.
11. I don't think I have a water pump problem. I think I still have trapped air in the system (I kept the heater on during all burping to get air out of heater core). I guess there still is the possibility I could also be putting combustion gases into the cooling system from a small head gasket/cracked head from all the banging and temp spiking. I checked the coolant level the next day, looked good and again, no signs of any problems in any of the fluids.
12. What is the recommended burping procedure? Should I just be patient and let this sort itself out - that choice worries me!. Has anyone had these same symptoms? Do I have a combustion leak and should I do the hydrocarbon test?

Please help, I'm going insane with this one.

[Authentic-242]

All ideas are welcome, c'mon boys I need ya!

1. Is it possible the water pump turns well enough at speed to keep temps down, but 'slips/has impeller wear' so at low rpm it can't push enough water to maintain temp? All belts are tight/not slipping as far as I can tell.

2. Should I take the thermostat out and see what happens to make sure it's not
closing intermittently or when surrounded by an air pocket and won't open?

[indymanjoe]

I havent had the noise you mention ever happen to me.the dieseling could be timing related and heat related i suppose.I think your post above #7 rules out head gasket as well.Do you have a clutch fan? is it working properly?When i "burp the coolant system" all it usually takes is running it and topping it off.I guess you could drive it on some ramps so the rad opening is the highest and go from there,If you put too much coolant in,it will just blow off what it doesnt need.Are you running an aftermarket gauge? or a factory type? If ya can get a infrared thermometer type(harbor freight 40.00) and check at the water crossover.wish i could help more.Keep us posted on what ya find.

[indymanjoe]

Do you know what your compression ratio is?I'm not familiar with your combo.

[LPete]

These cars aren't prone to trapping air (nothing like some of the newer ones). It can help to jack up the front as high as you can get it, but I'd be surprised if that's necessary.

What is the flow like through the heater core? Do you have A/C and a heater valve? If there's good flow, with the heater on and blower on high, the outlet hose should be the same temp as the inlet. If the heater circuit is flowing, I'm not sure the bypass passage from timing cover to intake is critical. If the heater circuit is closed, it's very important. I had a new Chevy small block water pump that the bypass hole wasn't drilled, and that thing acted crazy -- it would sit there and hammer until the thermostat eventually opened, then it'd cool down a bit, and repeat the cycle.

If yours is fine without a thermostat, I'd suspect a bypass problem -- either heater flow or the bypass passage, or both. Hope this helps.

BTW, is your temp sender by the thermostat in the intake crossover?

[Authentic-242]

1. Aftermarket temp gauge, likely not overly accurate, but shows wide changes in temp from a 'relative' standpoint and the loud banging confirms something isn't right.

2. The small chamber heads likely put C.R. at 9.5-10:1 (which I know is high for today, but I haven't really had any detonation problems under load or otherwise before this all started. I believe the pistons are original as I have only owned the car for just under a year. As stated earlier, the stuck open thermostat kept everything cool last year and lower temps will definitely keep it from detonating (and hide a bypass problem) and I do run 93 octane Sunoco.

3. No clutch fan, 5-blade stock, aluminum radiator, AC yes, heater blows just fine and hot. I do have nose elevated to some degree during burping.

4. Temp sensor mounted in intake to the right (looking from front of car) of thermostat housing.

5. As none of this started before I replaced the faulty thermostat (along with other things) last year, it is possible a bypass problem that was hidden has now surfaced. Perhaps even causing the thermostat to fail during previous ownership. I'm going to pull the thermostat today, retest in kitchen, and see how much running without it changes the problem I'm having.

Thanks, keep em coming/stay tuned

[rolling money pits]

sounds, no pun intended, like it might be a WP clearance issue. or at least that's part of the issue.

i had same engine set up years ago, .030 over 400 with 62s, and while the car would get pretty warm, never an issue like you have. and this was long, long before i ever even heard of a WP clearance issue. i just slapped on the new one and let it ride. what pistons are in it? if it's the old school cast alum TRW style, static compression isnt an issue.

if you havent already, peruse the two stickied threads in the cooling section. should provide you with valuable info.

your description of it running cool at speed, then spiking(erratic) while at a standstill screams of WP clearance issues.


FWIW my car had a fixed four blade fan, and at idle it would draw a crap ton of air through the radiator. could drop a piece of paper a foot in front of the grille and it would get sucked into it. a fixed ( non-flex) five blade should be equal, or better, at pulling air.

do you have an overflow/expansion tank? if no, get one, a good one.

when was the last time the WP to DP sleeves were changed?

[Authentic-242]

1. Don't know what pistons are in the motor, not a lot of paperwork. I believe the rotating assembly is stock.

2. I pulled the thermostat today and tested in kitchen. It opened a bit higher than I remember last year by about 10deg. Its a 160 and was fully open by 180deg with a slow ramp up. I took it up and down in temp a few times and it seems like its functioning. I sealed the thermostat housing without the thermostat and will refill Monday, burp and see what happens - heading to Musclepalooza tomorrow in West Lebanon, NY to see what nice running cars look like I'll report on progress later - enjoy the weekend boys

[north]

Did you check the functionality of the water cut-off valve (Vacuum control of hot water to the heater on A/C cars)?

Also something stupid like a chunk of the old thermostat gasket feel into the system and is blocking a passage somewhere?

[Authentic-242]

Did a few things in parallel the last day or two so not entirely sure which one helped the most, but now we can start narrowing things down.

1. Removed thermostat, checked out Ok in pot of water, resealed thermostat housing without thermostat.

2. A forum member suggested I pull the 5/8" heater hose off the back of the passenger side head as I refill the cooling system and wait for coolant to come out to force air out of the back of the head, which I followed.

3. In the picture below is a valve installed by a previous owner. (1) valve goes in the 3/4" heater hose between the water pump and heater core nipple at the firewall. (1) valve goes in the 5/8" heater hose between the heater core nipple at the firewall and the back of the passenger side head water inlet. When the valves are manually closed the flow of coolant is cut-off from entering and exiting the heater core. This is the way I received the car. I was under the impression that since the car was from Florida (and its hot) that it helped keep the passenger compartment cooler by cutting off the heater core flow. I would open the valves when burping the system of air after coolant change or service, but would close them again like I received the car. One of the hoses was damaged so it also helped to keep the valve closed until I got around to replacing it.

4. Today I bought all new heater hoses and installed them as the factory did and removed those added valves. I refilled, got car running, saw EXCELLENT water pump flow without the thermostat in the radiator, let run about 20 min and no temp gauge spiking or loud knocking after shutdown.

5. Took car for 15-20 mile spin, no temp spiking whatsoever, no detonation or knocking when returned from trip. It appears that part of problem is solved.

6. Temp gauge ran cool (150 deg) without the thermostat and I know at some point I want to run with a thermostat for the good of the engine.

So here are my thoughts. (2) valves closed and stuck open thermostat when I received and drove car last year with no big cooling issues. (2) valves closed and working thermostat started cooling problems/spiking/knocking. (0) valves and no thermostat with no cooling problems. I don't know the purpose of those (2) valves. When I burped the car today the heater put out plenty of heat, when I test drove with heater controls off, there was no heat coming in the cabin as you'd expect (so why the valves?). Those valves cut off coolant to back of passenger side head - is that part of the bypass circuit that some have mentioned? So was it the closed valves or trapped air or both? With the valves gone, could I put a thermostat back in and expect all to be well?

[north]

Now it makes sense, I guess someone added those valves to cut hot water flow to the heater but God only knows what they had to do with your problem. Throw in your thermostat and see what happens.

[AJD1964]

Just a wild guess, but I'm wondering if those valves may have created some type of flow "turbulence". It doesn't look like a straight shot from inlet to outlet of the valves.

[LPete]

Just want to talk a little more about the bypass circuit. With the thermostat closed, there's no circulation inside the engine -- the water pump isn't really doing anything. The bypass is added to provide for circulation inside the engine with the thermostat closed, otherwise hot spots develop in the cylinder heads. That's what you're hearing -- water boiling inside the engine. The coolant in the intake crossover doesn't heat up, so the thermostat doesn't open, even with the boiling coolant in the heads.

A few cars I've seen have no bypass circuit -- they use the heater core for that. In that case, if they have a heater valve, there's a connection in the valve that allows for flow even with the heater flow shut off.

Pontiacs with heater valves depend on the bypass passage from intake manifold to timing cover for the bypass flow when the heater valve is closed. I suspect that yours is plugged. I'd bet you'll be fine with the heater circuit open, though.

One more note: most cars with AC only turn off the heater flow on "max air". The heater core is flowing otherwise, and the blend door closes to shut off hot air.

[Authentic-242]

Thanks Lee. It appears I don't have a vacuum controlled heater valve that I can see, whether it was delivered that way I can't say as you state you've seen cars like that. The manual valves I took out of the heater hose lines I'd say perform the same function as that missing valve (to cut off flow to heater core) and I've seen that manual valve (nearly identical) to what I removed in the resto parts catalogs for that same purpose. This is usually mounted between the 5/8" heater hose from heater core to passenger side head, although mine were in both heater core hoses. Mine has always been a southern car and perhaps previous owners have been content leaving it configured for max. AC more often than for heat. My AC compressor can spit oil so I basically leave it off to minimize a mess under the hood till I straighten that out also. I also believe the coolant bypass you describe between the intake and timing cover (if blocked) can't be confirmed unless I remove the water pump - correct? The car has been driven a few days in a row now and other than the engine running too cool from lack of a thermostat everything appears to be fine. With my heater core in the loop now and acting as the bypass circuit (if the bypass in the timing cover is plugged) I should be able to reinstall the thermostat with no ill effects - correct? If that is successful, should I install the missing vacuum controlled valve and see what happens before ripping apart the water pump to view something that may be just fine? How do I know what vacuum valve is correct for my AC config?

[Squidward]

Originally Posted by LPete

Just want to talk a little more about the bypass circuit. With the thermostat closed, there's no circulation inside the engine -- the water pump isn't really doing anything. The bypass is added to provide for circulation inside the engine with the thermostat closed, otherwise hot spots develop in the cylinder heads. That's what you're hearing -- water boiling inside the engine. The coolant in the intake crossover doesn't heat up, so the thermostat doesn't open, even with the boiling coolant in the heads.

A few cars I've seen have no bypass circuit -- they use the heater core for that. In that case, if they have a heater valve, there's a connection in the valve that allows for flow even with the heater flow shut off.

Pontiacs with heater valves depend on the bypass passage from intake manifold to timing cover for the bypass flow when the heater valve is closed. I suspect that yours is plugged. I'd bet you'll be fine with the heater circuit open, though.

One more note: most cars with AC only turn off the heater flow on "max air". The heater core is flowing otherwise, and the blend door closes to shut off hot air.

Don't forget that bypass hole that connects the crossover to the timing cover. It's a constant bypass that keeps coolant circulating when the tstat is shut. When the tstat opens, it just creates an additional large parallel path to generate a d/p and flow across the radiator.

It becomes a balance of the 3 parallel flow paths: radiator, heater core, and timing cover bypass.

OP: has the radiator been flushed?

[sts]

<what they had to do with your problem<

It's called water hammer. If you take a length of water pipe, install a "t," extend a length of pipe, and cap the extension, it will make a hammer noise when turning water pressure on and off. I don't know why because I'm not an expert on the subject. You might find water-hammer information with a google search; I have other things to do.

As for a subject I do know, there isn't any special coolant filling methods for a Pontiac v8. As someone already mentioned, fill it up, cap it, run it around town, let it cool, top it off, and it's done.