Absolutely stumped with cooling

[PilotInASpider]

Hi all, I have a ‘79 Spider 2000 with a recently redone head gasket. It will not stop overheating. I have read almost every forum post and tried various things with no luck. My problem is with the thermostat. After bleeding the system properly according to the Vick Auto instructions, the two upper radiator hoses get hot but the lower hose and the lower half of the radiator stay cool. I took out the thermostat and drilled a hole in the lower outlet to let air bubbles escape and I boiled it and confirmed it opened at 205 degrees F. I’m not sure if there’s air still caught in there (unlikely with the hole in the thermostat) or if I need a new thermostat. I am stumped and just want to drive my spider without having the gauge read above 250 F. Thanks for any responses.

[wetminkey]

I have no idea what Vick's recommended, so here's how I fill mine from empty.
Fill radiator as much as possible, apply cap. Fill through passenger-side upper coolant hose (while disconnected at the coolant-T) until fluid runs out of the coolant-T, reconnect hose. Fill through coolant -T plug as much as possible. Apply plug.
Jacking the front-end slightly can assist, as can occasionally 'rocking' the car, to help release trapped air.
Be sure that the coolant reservoir is to proper level, line to it is clear, and cap is good.
Folks have added a coolant fill to their heater hose coming from the rear of the head, but I found no benefit in my addition of the thing, and find that it gets in the way of access to spark plug #4, and it's wire,...I might actually remove it. I don't have problems filling my cooling system, as is,...
Are you dealing with a factory-type, external thermostat? Sounds like what you've got, works - at least now.
You didn't have the same lame-brain mechanic that I inherited my Spider from, did you? He decided that if one thermostat was good, maybe two was better, and installed an "in-head" T-stat to complement the factory external one - nothin' but bad news!
I hate to ask, but was it overheating before the head gasket replacement,...or did it start after that? Or was it not running enough to know,...?
Todd.

[tima01864]

I will add: Fill the radiator slowly to Wetminkeys procedure, I fill with a measuring cup letting the coolant displace air.

[18Fiatsandcounting]

I’m not sure if there’s air still caught in there (unlikely with the hole in the thermostat) or if I need a new thermostat.

Is it possible that the thermostat is installed incorrectly? With the 3-neck design, it's very easy to put it in "backwards". It should be installed so that the connection to the water pump inlet is open to either the hose that goes to the T-connection at the top of the head, or to the lower radiator hose. But not both, except for a brief period when the thermostat is "opening" and switching from one to the other.

To check this, you pretty much have to take out the thermostat and test it cold and then in a pot of boiling water.

-Bryan

[PilotInASpider]

I’m sure it is in the right way. I took it out and inspected it while I drilled the hole and boiled it. The weird thing is that I had it working last week after bleeding the system. I took it for a drive and it didn’t overheat. Then I try to drive two days later and it started overheating again. I guess I could have a clogged radiator but when I took the thermostat out coolant flowed from the bottom hose outlet just fine. I am so confused

[PilotInASpider]

I have no idea what Vick's recommended, so here's how I fill mine from empty.
Fill radiator as much as possible, apply cap. Fill through passenger-side upper coolant hose (while disconnected at the coolant-T) until fluid runs out of the coolant-T, reconnect hose. Fill through coolant -T plug as much as possible. Apply plug.
Jacking the front-end slightly can assist, as can occasionally 'rocking' the car, to help release trapped air.
Be sure that the coolant reservoir is to proper level, line to it is clear, and cap is good.
Folks have added a coolant fill to their heater hose coming from the rear of the head, but I found no benefit in my addition of the thing, and find that it gets in the way of access to spark plug #4, and it's wire,...I might actually remove it. I don't have problems filling my cooling system, as is,...
Are you dealing with a factory-type, external thermostat? Sounds like what you've got, works - at least now.
You didn't have the same lame-brain mechanic that I inherited my Spider from, did you? He decided that if one thermostat was good, maybe two was better, and installed an "in-head" T-stat to complement the factory external one - nothin' but bad news!
I hate to ask, but was it overheating before the head gasket replacement,...or did it start after that? Or was it not running enough to know,...?
Todd.

It just has the external thermostat. I have basically narrowed it down to that or the radiator because the bottom half of the rad and the lower hose are cool. The PO said it was overheating before but I assumed that was because of the head gasket (probably assumed wrong). I have the top filler tee above the valve cover and am pretty sure I got most of the air out by putting coolant into the block from the tee. It’s a fairly simple system once you understand it so I’m not too worried. Just a little confused as to why my stat won’t open. Maybe I just have to shell out for a new one thank you for the input!

[tima01864]

https://www.mirafiori.com/124/cooling.html

[18Fiatsandcounting]

Based on what you've described, it sounds like a bad thermostat. It sounds like water is running through your radiator, so it's not completely plugged, and it sounds like you've taken pains to get enough coolant in the system. Other than the thermostat and the water pump, there's not much else to go wrong.

One question: Does it immediately overheat, or just creeps upward over time until the point where it's above normal? If the former, probably a thermostat issue. If the latter, probably a cooling system that isn't up to snuff (partially plugged radiator, not enough coolant, fan not coming on, etc.)

-Bryan

[SteinOnkel]

Fill system best you can. Get a radiator test kit. Pressurize the system. Make sure it holds pressure, if not, stop and fix it.

If it does. Let the pressure out, top off system. Repeat this 4 or 5 times as necessary until your radiator is full.

Boil a BIG pot of water. Run engine and bring to operating temperature. Pour boiling water over thermostat. It will then open and let the last air bubbles escape. Let everything cool off, then top of radiator.

Done.

[Nut124]

I have never had to do any of these extra procedures to bleed the cooling system after filling it. I just jack the front of the car up and pour coolant into the radiator, then squeeze the hoses to work air out with the cap open. I have always assumed that the thermos is not bubble tight but some might be. I have drilled/tapped a small bleed hole on top of the T for a little final bleed off.

If the thermos indeed tests to be bubble tight, then I would consider drilling a very small hole in the plate. What size hole did you drill?

I would double and triple check the thermos orientation. That is what I have to do. I mark the ports with black marker and arrows after I study it or I get confused. There is a mistake somewhere of defective components.

The port that is always open goes to the pump inlet. The port that is closed at room temp goes to bottom rad hose. The port that is open at room temp goes to top T.

One thing to note: One cannot determine orientation based external looks of the thermos. I have seen some that have the thermos shaft inline with the pump port, others where the shaft is perpendicular to the inlet port.

[PilotInASpider]

Update: at this point I am just flummoxed. I spoke to the PO and he said that he replaced the thermostat and radiator himself with new parts. I drilled a 1/4” hole in the lower rad side of the stat. I know it is on the right way and opens before a boil. I have a couple of ideas: 1. My temp gauge was reading way off (before I lost power to my gauges ). 2. My heater core is somehow the problem and I should remove it from the coolant circulation. 3. My block is clogged? I replaced the head gasket and water pump so I know those are good. Maybe I’m just freaking out but when it gets hot the fan won’t come on. I just replaced the fan switch with a low temp. one from Mark. If anyone has any other ideas please let me know. I am pretty sure I am bleeding it right and the hoses get hot so I know water is in circulation through the block. Today I removed the ‘stat and put in a tee of metal pipe for a test. I let it get hot and the fan still wouldn’t come on. As I said I am just flummoxed. One important note: I had it driving without overheating. Then I tried to drive two days after that and it overheated again. Thank you to everyone for the responses. I have no idea what to do at this point

[Nut124]

If you have concerns about the instrument cluster wiring, then I would address those first.

I would check the cooling fan function. The fan should come on after idling for 10min or so. To test the fan, disconnect the new low temp radiator fan switch and short the wires on the harness side. The fan should run now.

The heater core cannot do any of this IMO.

I'd replace the temp sending units in the head.

Why did you replace the head gasket? Did it show evidence of overheating?

Did you double, triple check the thermostat plumbing for correct arrangement?

[PilotInASpider]

If you have concerns about the instrument cluster wiring, then I would address those first.

I would check the cooling fan function. The fan should come on after idling for 10min or so. To test the fan, disconnect the new low temp radiator fan switch and short the wires on the harness side. The fan should run now.

The heater core cannot do any of this IMO.

I'd replace the temp sending units in the head.

Why did you replace the head gasket? Did it show evidence of overheating?

Did you double, triple check the thermostat plumbing for correct arrangement?

The fan works. It has power and if I ground the wire coming from the fan it turns right on. I’ll replace the temp sending units and deal with my gauge cluster power soon hopefully. There was foam in the oil and oil in the coolant so I knew it was a head gasket. As for the thermostat I know it’s on the right way. The side that’s closed at room temp was and is going to the lower rad hose. The side that closes when hot goes to the upper hose to the T. The middle goes to the new water pump. I also drilled a 1/4” hole in the bottom side of the ‘stat to let air bubbles through but it still overheats.

[SteinOnkel]

Ah, I missed the part about the head gasket replacement. Therefore, lemme repeat:

Get a radiator test kit. Pressurize the system. Make sure it holds pressure, if not, stop and fix it.

This should be standard operation after any cooling system work. If the system can't hold pressure, all sorts of strange things start to happen.

[PilotInASpider]

Update: everything is working perfectly! And I suppose it always was... the problem was the temp senders in the head. I was told to unplug one and now the gauge reads perfectly. I re bled the system, jacked up the front with the rad cap off and turned it on. It slowly came up to 195F and the thermostat opened. Shortly thereafter my low temp fan switch kicked in and I let it run two fan cycles before capping it and shutting it off. A huge thank you to Mark Allison who supplied the low temp fan switch and told me to unplug one of the senders. Now it’s time to hit the open road with the new 32/36 installed! Thanks to all for the help on this problem.

-Sam