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1994 mustang overheating after hci swap

6K views 44 replies 10 participants last post by  hyyeguy123 
#1 ·
I have a 94gt auto with 58,000 miles. I recently aquired a set of heads and decided to do the full hci swap. Here is a parts list of everything I put on:

gt40p heads with beehive comp springs
trick flow stage 1 cam
gt40 upper and lower intake
70mm tb
bbk cai
bbk equal length headers
bbk underdrive pulleys
deleted ac and power steering

after initially finishing the swap I was immediately having overheating problems. It was getting hot way too fast and coolant was spewing out of the overflow. After a couple of days of trying to figure out what was going on I realized I had the water pump pulley spinning the wrong direction. So i bought a new belt and now have the water pulley spinning counter clock wise. I started it up and it was cooling fine, took it for a spin down the road (about a 2 minute drive) just to make sure it was cooling like it is supposed to and came back. Everything seemed fine. The wife and I decided to go out tonight and I wanted to take my car since I have it in running condition now. I did a quick check over and noticed that the overflow was almost empty, so I filled it a little above the cold mark. Well, we go to leave and 2 minutes down the road the car starts overheating like crazy again and coolant is gushing out of the overflow tank again. I let it cool for a few hours and just tried starting it up a little while ago but now it overheats as soon as it gets to running temp, and the upper radiator hose looks like a balloon that is about to burst. I checked temps at the heads and the water neck with a laser, 230-240 around the water neck and lower intake, and it said any where from 215 to 250 on different parts of the head. i am

Is the thermostat not opening up?
Is the radiator cap bad?
Do i have too much/not enough coolant in the system?

I had read a few other threads suggesting blown head gasket leaking into the coolant system but i really don't think that is the case here. Because it had the symptoms, i fixed the problem and the symptoms went away and now the symptoms are back but slightly different. also, the car is running great aside from this overheating issue. Also not to mention I just put these damn head gaskets on.

What do you fellas think? I am really at a loss. It seems like one issue after another and when I finally think i can drive it BAM here is something else you need to fix.
 
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#2 ·
You did install the thermostat with the spring facing the correct direction didn't you? Spring on the thermostat should face the engine. If the upper radiator hose is swelling badly something is definitely not right. I know it sounds trivial but are you 110% sure you installed the head gaskets the correct way? Each one has a front and an arrow on it so it will line up properly with all your cooling jackets in the block. Lastly have you checked to make sure the water is even circulating through the engine? You can let it idle with the radiator cap off and you should be able to see movement in the water if the thermostat is open. A quick and cheap thing to try is a new thermostat. Also are you running the stock clutch fan or an electric? If you have air in the cooling system and it won't burp itself you will have it overheat almost instantly. You can jack up the car on the side of the radiator cap and squeeze your upper radiator hose a bunch to help relieve the air trapped inside. And lastly many high performance thermostats have a hole drilled in them that allows a little antifreeze to circulate before the thermostat opens. Those are good also as they help to prevent any air being trapped in the cooling system.
 
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#3 ·
I'm almost 99% sure I installed the thermostat correctly, but I'm praying that I put it in backwards. I'll be taking it off and looking today, and either drilling the hole in it or buying a new one with a hole. I'll also get a new radiator cap. I'm not sure I quite understand about seeing the water flow in the radiator though. Like rise and drop? I'm also 99% sure I installed the head gaskets correctly. The tabs are poking out the front side of the engine on both gaskets.
 
#4 ·
A couple years ago I put a thermostat in backwards in a mustang and it did NOT overheat. In my experience it ran very cool. I believe the flow of the water overcame the spring pressure and allowed water to flow. I realize these pumps are not positive displacement but that is what happened to me.

Seeing flow in the radiator means with the thermostat open and the cap off you can visually see liquid rushing in near the top and heading downward. If you just see stagnant fluid sort of raising and dropping a little you either have air in the system or a plugged radiator.

You didn't happen to plug the rad and pump with rags while the car was apart did you?
 
#6 ·
I did put some rags in the radiator but i took them back out before reinstalling? also, i don't see water flowing through the radiator, but i am going to assume that is because i had a lot of air in the system. if not, i would rather it be a clogged radiator than something wrong with the head gasket.

headgaskets not installed correctly can give similar issues
i really hope this isn't the situation.

Alright, i took the tstat out. i had it installed correctly. i also did a boil test on it. opens up properly. i bought a new radiator cap today. when i took the tstat out, no coolant gushed out. i am assuming because all of it gushed out of the overflow. so i will reinstall the tstat, add more coolant and burp the system again tonight. if that doesn't work then my next fix will be getting a new radiator.
 
#7 ·
You can prove the radiator thing in like 10 minutes. Leave it a little low, cap off, run it in the driveway. When you feel a little heat in the engine shine a flash light in the rad. You will literally see water flowing in a stream out of the coils and into the tank headed back to the water pump. If you don't see this then there is no flow. Is the pump spinning the right way?Also a badly scaled radiator will restrict almost all flow. With the coolant low take a picture of the inside of the radiator.

Warning. I'm sure you know this but: don't put eyeball right in the radiator fill while it's running. And if the ethylene gets all over the driveway because of a burp or something keep the kids and the pets away from it.
 
#8 ·
I definitely am now thinking the radiator is clogged. Because i am not seeing anything flow in it. Before i started the hci swap, my car would overheat on really hot days and it would always overheat when i turned on the ac so i am thinking i have a plugged radiator core. Could this also be from a head gasket covering coolant passages though? I was thinking, if i installed the water neck without the tstat and tried to flush the system with water, will the head gasket prevent coolant or water from flushing out the lower hose? would that be a good test?
 
#9 ·
I cannot say much about the head gaskets and the symptoms if installed backwards. I mean they are marked front. I would have to see what is covered when they are installed backwards to even comment.

Others here have said it would cause overheating. Maybe they can comment why.
 
#10 ·
I ordered a new radiator, mine is 22 years old so it probably needs replaced anyway. it was only like $60 on ebay for a new stock replacement. i had read somewhere to pull a coolant plug from the front of the block and if you can stick your finger through it or a piece of wire and get coolant then your gasket is on backwards. apparently the gaskets are supposed to block the coolant passages on the front of the engine and open on the back? can anyone confirm this? also, the tabs for both of my gaskets are sticking out on the front of the block which i have read is the correct orientation.

i really hope the new radiator will solve my problem. how are you supposed to work on the cooling system without having to fork out $15 every time you need to add more coolant?
 
#15 ·
I noticed that you also installed underdrive pullies. I have never personally had any luck with those. Always had overheating problems and under charging problems. Will never run them again on the street.
 
#16 ·
I am using the water pump pulley and the crank pulley, but left the stock alternator pulley on.

Look inside the old radiator you should be able to see scale. Post a picture. You need a thermostat and I wouldn't leave straight water in there too long without a corrosion inhibitor package.
I will do that when i get the chance. I plan on putting the tstat back in and coolant when i get the chance too. I was just using water for the time being incase it all exploded back out again so i didn't have to waste more coolant.
 
#17 ·
well sh*t, i drove maybe a total of 6 miles and it started overheating and spewing out coolant again. i guess the new radiator helped with the coolant flowing better so it just took longer to happen. anyway, i started tearing it down tonight. hopefully i can get down to the block before bed time lol. i will keep the thread updated.
 
#24 ·
i had considered this being the issue, but underdrive pulleys wouldn't create back pressure causing coolant to spew out of the system. i will give it a try but i really don't see how they could cause it. i can understand overheating because the water pump pulley spins slower but not this. there was rust stains by the back 2 valves on the driver side head. maybe there was a leak.
 
#28 ·
okay, don't test it.

and just assume, it works.



if it does, and the system is burped of air, you have a crack in the block/heads, you can check for combustion gases in the coolant.
 
#30 ·
Maybe I missed it but you have the correct rotation water oump and belt routed correctly for it? Did you replace the thermostat yet? You might not always see the blocked cracked.
 
#33 ·
I checked the pressure and 16 pounds held without a problem.

So if something were cracked then the car would be staying cool. My car is definitely getting very hot. I think it's the wAter pump. If not then it's the pulley. I really hope it's the pump and not something simple like the pulley. I'd feel so stupid.
 
#37 ·
Here's what I did:

I removed the radiator cap. I placed the coolant system pressure checker on the radiator with the supplied radiator cap adaptor. I pumped to 16psi (what the coolant system is rated for) and let it sit for an hour. I checked every 15 minutes watching to see if the pressure would decrease and looked the engine over for leaks. Pressure stayed almost right at 16psi and I couldn't spot any leaks.

Is there another method?

Believe me, I'm not intentionally skipping any steps. Keep in mind this is the first time I've worked on a car this extensively.
 
#38 ·
Two questions: Which head gaskets did you use, and is there any coolant in the oil?
 
#45 ·
Well guys, after finally getting some time to put it back together and then solving a no-spark issue, the car is running like a champ. Now i just need to finish tuning it and time it properly. I think it was the water pump because that was the last thing I replaced. Thanks for your help guys!
 
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