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76’ 400ci overheating bad

K5wrench said:
I just recalled an epsisode of vapor lock my 76 k5 with the 400 had.
Could have happened to and sbc but i so happened to have that same k5.
It was outside Ely Nevada and 100 degree day.
Kept stalling on those passes.
For whatever reason, I pulled the gas cap and a blast of pressurised vapor came out.
My vent line thru thr canister was plugged by prev. Owner.
Fixed it.
Still had issues.
Replaced fuel pump.
Still had issues.
Tightened top of carb.
Problem solved.

But any one of those things could have been the issue.
The plugged fuel tank vent was bad but wasn't the cause of the stall.

Sometimes it just takes a steadfast approach of following each problem and correcting them.

I would start by actually verifying the coolant is getting too hot.
Use a seperate thermometer.
If it is, check that the thermostat is opening, or not in backwards.

If the coolant is only reaching 180 at the top hose and perhaps 150 at the bottom hose, you don't have an engine over heat problem.
Click to expand...

I thought same thoughts. The gas cap is good. New tank and sending unit. Vent tube is good. Yesterday I noticed carb bolts were loose. I tightened them but not much. Today it almost vapor locked.

Still. Should there be that much heat on the trans and floor?
 
Started it up and trans fluid is a little above OK mark on the stick.

Embarrassed to say how much I paid. It was a lot. I wanted the numbers matching and original aspects of it and paid the price. I just want the damn thing to be reliable. Want to keep this engine block.
 
Trans sounds like an issue so far.
 
Get one of those digital laser thermometers. I bought one for service work on furnaces and now I use it all the time. Real cheap, especially on amazon etc. It will allow you to start to pinpoint where all the heat is coming from. If the engine is 250 deg but the trans is 350 deg you would know where to start looking. Same goes for exhaust, radiator etc. Thermometer will really help quantify what "hot" really means on these different components and help steer you in the right direction. It would suck to pull a head and find out the heat was coming from the trans or something. With the engine not boiling over this sounds like something else is screwy.
 
CraigFulton said:
Started it up and trans fluid is a little above OK mark on the stick.

Embarrassed to say how much I paid. It was a lot. I wanted the numbers matching and original aspects of it and paid the price. I just want the damn thing to be reliable. Want to keep this engine block.
Click to expand...

Don't be embarrassed, that's some really nice looking early iron. Any one of us would love to have it in the fleet. Work through the issues and you will have a real nice classic to enjoy. The prices on clean early ones have gone up quite a bit, there are not a lot of really good ones left.
 
was just going to say i.r. temp gun and start checking stuff .

exhaust on pass die could be heat soaking the fuel and trans lines on that side .

and a good y-pipe 2 in to 1 and single muffler would flow just as good or better and keep the heat off the pass side .
 
Spoke to the guy I bought it from. The heads were replaced with another set of 400 heads. He said the guy that built it is well versed in 400s but I’m calling tomorrow just to confirm. Original head had a crack in it.

I’ll get a digital temp gauge and give you guys a report of all the component temps.

Really appreciate the advice. This forum is awesome. I have another super car I work on and the douche bags on that forum don’t know a damn thing about working on them. This is restoring my faith in man kind :bow:
 
sweetk30 said:
was just going to say i.r. temp gun and start checking stuff .

exhaust on pass die could be heat soaking the fuel and trans lines on that side .

and a good y-pipe 2 in to 1 and single muffler would flow just as good or better and keep the heat off the pass side .
Click to expand...

When I install EFI I’m using the rubber vapor guard hose and running it outside the frame and no where near the exhaust.

Should I wrap th exhaust with thermal wrap?
 
CraigFulton said:
Spoke to the guy I bought it from. The heads were replaced with another set of 400 heads. He said the guy that built it is well versed in 400s but I’m calling tomorrow just to confirm. Original head had a crack in it.

I’ll get a digital temp gauge and give you guys a report of all the component temps.

Really appreciate the advice. This forum is awesome. I have another super car I work on and the douche bags on that forum don’t know a damn thing about working on them. This is restoring my faith in man kind :bow:
Click to expand...
we like super cars

does it do burnouts?
 
I like that you said "another supercar".
Like a K5 is a supercar.
I think they are too.
 
Just a stupid question here... But you have the trans cooler and all hooked up right? Also If the trans lines are running with the fuel lines and the trans is getting that hot, your cooking the fuel there and insulating it the way the pic looks may have made it worse.
 
Ah. I relooked at that pic and realized it's behind the trans lines lol
 
When I install the EFi I will have all the thermal wrap from the fuel lines. Should I wrap the trans lines near the exhaust and wrap the exhaust?

I’m doubting our steam vent theory in the heads based on convo with previous owner. But he claims up and down none of this happened before rebuild.

Wouldn’t engine overheat if steam vents were issue?

Still working on the iR temp gauge later tonight.
 
CraigFulton said:
When I install the EFi I will have all the thermal wrap from the fuel lines. Should I wrap the trans lines near the exhaust and wrap the exhaust?

I’m doubting our steam vent theory in the heads based on convo with previous owner. But he claims up and down none of this happened before rebuild.

Wouldn’t engine overheat if steam vents were issue?

Still working on the iR temp gauge later tonight.
Click to expand...
The steam gets trapped in the block if the heads and gasket are not drilled.
The 400 has siamesed cylinders that create a pocket that must be relieved.
Otherwise the steam pocket displaces water between the cylinders causing a hot spot and overheating.
It is a well known issue with the 400.
But, like i said, probably not your problem.
But cannot be ruled out either.
But id try everything else first.
 
K5wrench said:
The steam gets trapped in the block if the heads and gasket are not drilled.
The 400 has siamesed cylinders that create a pocket that must be relieved.
Otherwise the steam pocket displaces water between the cylinders causing a hot spot and overheating.
It is a well known issue with the 400.
But, like i said, probably not your problem.
But cannot be ruled out either.
But id try everything else first.
Click to expand...

Aside from measuring the temp on everything I don’t know what else to try. I guess that will tell us where to go next? Any specific areas I should measure the temps?
 
CraigFulton said:
Aside from measuring the temp on everything I don’t know what else to try. I guess that will tell us where to go next? Any specific areas I should measure the temps?
Click to expand...
Upper and lower radiator hoses.
Thermostat housing.
Trans cooler lines.
 
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