'99 engine swap into '96--overheating question

[pottsy]

Kind of a long post but anyone that has had experience with working on these cars, please read:

I have been helping with a '99 Cobra engine swap into a '96 Cobra. Everything has been swapped into the car, the wiring has been properly modified, the returnless fuel rails were retained, kept the stock plug wires....and it starts up and runs every time. Unfortunately there is a problem with the car--it keeps overheating. This '96 has had the cooling recall and when the '96 engine was in it, it never overheated.

The problem is that the car gets up to "operating temperature" and stays there for a few minutes, and then it begins to overheat...quickly. A couple of times the coolant reservoir has literally boiled over and spilled coolant onto the pavement (while driving)!

We've gone through four thermostats, boiled them to make sure they are opening at the ideal temperature (the first two were bunk). The fan is coming on. We have been using about a 70/30 mix. We pressurized the system twice and it seems to hold at 16 psi alright for a decent amount of time, so we don't think there are any issues with the headgaskets or heads. The system has been cleaned well more than once, and we've jacked the car up high each time we fill it to keep air out of the system (as well as the proper fill method). We know the thermostat is allowing flow because the hoses on both sides are warm to the touch after operating. So we think it may be the radiator, but there may be something we somehow overlooked...

Anyone have any ideas what could be causing this problem? This car is up and running great except for the overheating....any suggestions would be appreciated, thanks.

 

[4.6 Rocket]

If there is air in the line it could be causing a problem

 

[Doug]

i would go over the wiring again for the fan and just slap a working thermo on there just to officially rule it out.

does the fan even come on?

 

[ZimStang]

My cooling problem ended up being a headgasket with symptoms like youre getting. It would go to operating temp (180*) and sit at like 190 for a while, then creep to 210*, sit there for a while... then creep way up to the 230 mark. I went through a couple tstats, had the radiator and water pump checked... and all was fine. Turns out, its the head gasket. Id check and see if you have any exhaust gasses in your coolant and that would tell you. Good luck, cooling issues suck as ive recently found out.

Edit: Maybe try a new radiator cap too?

 

[pottsy]

If there is air in the line it could be causing a problem

We've completely ruled that out.

i would go over the wiring again for the fan and just slap a working thermo on there just to officially rule it out.

does the fan even come on?

We got a thermostat that opens at 170-ish and is fully opened at 192-193 (stock)...so we know that works, and we can rule that out because the hoses on both sides of the t-stat are hot...meaning that the thermo is flowing as it should.

The fan definitely comes on, we verified that a few times although it does sound like a more likely culprit seeing as how once the car gets to operating temperature for a few minutes it then overheats as if there's nothing cooling the outside of the motor down...

My cooling problem ended up being a headgasket with symptoms like youre getting. It would go to operating temp (180*) and sit at like 190 for a while, then creep to 210*, sit there for a while... then creep way up to the 230 mark. I went through a couple tstats, had the radiator and water pump checked... and all was fine. Turns out, its the head gasket. Id check and see if you have any exhaust gasses in your coolant and that would tell you. Good luck, cooling issues suck as ive recently found out.

Edit: Maybe try a new radiator cap too?

A headgasket is still a distant possibility, the first system compression we did it would drop from 16 psi quickly, and the second time we developed a loud leak from the passenger-side-most heater hose at the firewall. After that, though, it held the compression well, which made us think it isn't the head gasket...but maybe the head itself? This is a used engine we are talking about, the valve cover on the driver's side has definitely been off (there is silicone in the spark plug holes indicating it's been removed before). There may be a more serious problem with this motor than we have discovered yet, we're just trying to remain optimistic...

A new radiator cap is definitely in order, the one on there right now is in shitty condition...but I didn't think the cap alone could cause such severe overheating...

 

[ZimStang]

A new radiator cap is definitely in order, the one on there right now is in shitty condition...but I didn't think the cap alone could cause such severe overheating...

Thats what I thought too... after talking to a couple guys at radiator shops they told me that if it doesnt hold the right pressure, itll start running hot and just keep working its way up. You might as well try it, if its the culprit, it was only 10 bucks that you end up spending.

 

[pottsy]

Thats what I thought too... after talking to a couple guys at radiator shops they told me that if it doesnt hold the right pressure, itll start running hot and just keep working its way up. You might as well try it, if its the culprit, it was only 10 bucks that you end up spending.

Ok, cool...good to know. Thanks for the help, the radiator is getting checked out and cleaned today as well so that will help eliminate some more possibilities.

 

[Tabres]

What about the water pump itself? I had to replace mine not too long ago because it was leaking horribly and I didn't replace it with the same exact factory model water pump. My car used to never run over 180* with the factory waterpump, but now its not uncommon to see 210* and have it creep up to 230* even.

I've played holy hell for ever now trying to keep my car cool. I've bruped it more times than I can count on two hands using every method I've come across, even had it professionally done with a specific tool for this, and it still runs hotter than it did before I changed the waterpump. I'm thinking the pump I have on the car now just doesn't have the same flow rate so to speak as the origional, because that is the only thing I changed. People keep telling me, "blah blah blah, its fine, blah blah blah, there's nothing wrong" but its all bullshit. I KNOW its not right and no one is going to convince me it is. Its not running at the temperatures it used to, plain and simple.