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Hey guys, I've made a post before but it was a couple months ago. I have a 1997 3000GT base, 4 speed auto FWD with the SOHC engine. Are there any SOHC engine heads on here?
I need to pick someone's brain, someone who knows about the engine and car. Specifically, can I just drop a DOHC in it with new wiring harness and ecu? Or do i need a new transmission as well? Will I have to use different engine mounting points, or just different engine mounts?

I also have a current overheating issue. I got the car about 3 months ago, with fresh coolant in it from 3 months prior. Changed the radiator cap, radiator, and coolant, as well as a new thermostat, and even used Royal Purple coolant additive that helps run 25 degrees cooler. I have about a 70/30 coolant to water mix, but i might add some more water. When i floor the car or drive it hard, even at night when its in the 60's or 50's, when i continually floor it, the temp slowly goes up. It used to go up real fast, but the old radiator also had some sort of build up coming out of it, and that fresh coolant that the previous owner had put it was all brown.

With a new radiator, thermostat, radiator cap, and new coolant, could I have a cracked cylinder or blown head gasket? Is that common on these things? Or maybe there is just rust inside the block from when it sat in a field for 4 years? After a whole new cooling system(except hoses and fans, fans still work fine), I shouldn't be heating up anymore.

Thoughts?
 

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93 NA ATX 3000gt DOHC
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but the old radiator also had some sort of build up coming out of it, and that fresh coolant that the previous owner had put it was all brown.

With a new radiator, thermostat, radiator cap, and new coolant, could I have a cracked cylinder or blown head gasket?
Coolant being brown is clear sign of oil mixing with it. Blown/leaking head gasket would be likely suspect and would account for overheating. Unless it was left without antifreeze for some period of time, cracked cylinder or head wouldn’t be likely. Also cracked cylinder would also allow coolant into oil, which would be seen as brown also.

I need to pick someone's brain, someone who knows about the engine and car. Specifically, can I just drop a DOHC in it with new wiring harness and ecu? Or do i need a new transmission as well? Will I have to use different engine mounting points, or just different engine mounts?
Haven’t personal tried this kind of swap. But suspect a DOHC will bolt right up to your transmission and motor mount points. Since motor mounts, torque converter are shown as same on all years of 3000gt’s. You certainly would need wire harness and maybe ECU (not sure) since ’97 SOHC NA uses MD339760 and ’97 DOHC NA uses MD339761, not sure what the difference of the last digit has. Also you would have some exhaust piping differences.
 

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?Mark
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I got sohc heads in southern florida for local pick up if u need them and are in soflo
 

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Discussion Starter #5
Coolant being brown is clear sign of oil mixing with it. Blown/leaking head gasket would be likely suspect and would account for overheating. Unless it was left without antifreeze for some period of time, cracked cylinder or head wouldn’t be likely. Also cracked cylinder would also allow coolant into oil, which would be seen as brown also.

Haven’t personal tried this kind of swap. But suspect a DOHC will bolt right up to your transmission and motor mount points. Since motor mounts, torque converter are shown as same on all years of 3000gt’s. You certainly would need wire harness and maybe ECU (not sure) since ’97 SOHC NA uses MD339760 and ’97 DOHC NA uses MD339761, not sure what the difference of the last digit has. Also you would have some exhaust piping differences.
Awesome man, thanks for the reply! Won't be swapping the engine in to leave the auto trans in though. Definitely gonna throw a 5 speed in there. The auto has lasted good and long though, 194k miles and its just now giving little jerky shifts into first, whether im putting it into drive or slowing down to a stop and it downshifts. It's not terrible, but definitely there

I should probably also mention, the car only overheats when i drive it hard. With the new radiator and stuff, it typically doesn't really happen unless im flooring it continuously. Still think it'd be a head gasket?
 

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Someone couldve mixed orange coolant with green? You should start with a radiator flush, and then drive it and see how it does over time. thats what I would do before taking out an engine anyways.
 

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Discussion Starter #8
Someone couldve mixed orange coolant with green? You should start with a radiator flush, and then drive it and see how it does over time. thats what I would do before taking out an engine anyways.
I already did a flush when i put the new radiator in, on the block
 

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So, the color of your coolant is changing after it runs through the engine?
Possibly a stupid question, but here goes: You flushed the entire system until the water was clear?

If the oil you're using isn't synthetic and you have water leaking into the oil via a blown head gasket the oil will be a milky color.

If it's blown into the cylinder you will have a "sweetish" smell at the exhaust due to the burning of the antifreeze.
Blowouts between cylinders cause missing and a low compression reading between the 2 cylinders.

If you decide the heads are okay and it starts to overheat and slow down in passing gear it's probably not your engine; I've seen my fair share of clogged catalytic converters cause this.
 

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Discussion Starter #10
So, the color of your coolant is changing after it runs through the engine?
Possibly a stupid question, but here goes: You flushed the entire system until the water was clear?

If the oil you're using isn't synthetic and you have water leaking into the oil via a blown head gasket the oil will be a milky color.

If it's blown into the cylinder you will have a "sweetish" smell at the exhaust due to the burning of the antifreeze.
Blowouts between cylinders cause missing and a low compression reading between the 2 cylinders.

If you decide the heads are okay and it starts to overheat and slow down in passing gear it's probably not your engine; I've seen my fair share of clogged catalytic converters cause this.
You were correct sir. After replacing my rack and pinion and having to cut the exhaust to do so, the overheating stopped entirely. Car runs like a dream now!
 

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One of the few advantages of owning over 60 vehicles, only 2 of them new :)
(Got my first one, a '54 Chevy, at age 13.)
I had a full size '87 Jeep Grand Wagoneer with the wrong smaller cat converter (installed by an ignorant muffler shop) that would slow down when I floored it. The converter had clogged just enough to let exhaust through at low speeds.

I'm glad I helped.
 
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