86interceptor

I finally got my 400sbc installed and fired up, I was running it to break in the cam and it keeps getting very hot and I have to shut it down. The last time it got so hot it busted that little rubber plug on the radiator right under the top radiator hose. any suggestions on what to do????

82 Iron Duke

iTrader: (21)

Thermostat?

86interceptor

its brand new but that does not always mean anything

82 Iron Duke

iTrader: (21)

My friend had that problem also, first he put the t-stat in backwards, then the new one didn't work. Try it for starters, and try the old one if all else fails.

Brandons'86T/A

Radiator Clogged some how? not flowing, Im just learing bout cars so that might sound Dumb, lol

Sonix

iTrader: (1)

400SBC? your heads and head gaskets have steam holes?

i'd remove your t-stat altogether then, for now.
cooling system is full? block is full of coolant?

84z28350

Mine did the same thing after a head swap last summer, it had an airlock. i just burped the hoses and fired it back up and all was good.

Air_Adam

Rob Wade

Take the thermostat housing off of the intake and remove the t stat. I bet you won't see any coolant. Now fill the motor through the hole in the intake until its full to the top. Re install tstat and housing. This should correct your problem if its an air pocket........as asked earlier, do you have steam holes in your head gaskets and heads for the 400?

DLV555

iTrader: (1)

Don't remove the thermostat permanently, that will just cause it to continue to overheat. The thermostat is a restriction in the cooling system and regulates the flow of coolant so that it spends enough time in the radiator to actually exchange heat with the outside air. Without the thermostat, the coolant with flow too quickly through the radiator and not cool down enough. What kind of condition is the radiator in? Is it up to the task of cooling a 400 SBC? Definitely check the thermostat for proper installation and check for air in the system like was previously mentioned.

86interceptor

I bought the engine as a longblock so I hope the guy I bought it from remembered the steam holes

8Mike9

[QUOTE=DLV555]Don't remove the thermostat permanently, that will just cause it to continue to overheat. The thermostat is a restriction in the cooling system and regulates the flow of coolant so that it spends enough time in the radiator to actually exchange heat with the outside air. Without the thermostat, the coolant with flow too quickly through the radiator and not cool down enough. QUOTE]

Wives tale.

Rob Wade

Tough call here. Your basically assuming somebody else did something correctly or knew that they needed to add steam holes to the heads/headgaskets. Unfortunately the only way to REALLY know if it was done properly is to tear it down. You can try a couple of things but the more you overheat that motor, the more damage you do and the more money you might cost yourself. If you think about the job of a tstat to control the flow of the coolant, it only makes sence. If your running down the highway at 3000 RPM for an hour the coolant just doesn't spend enough time in the rad to cool off. At lower RPM it might not be an issue but take it on the highway and watch the temp rise. Every vehicle has a tstat, must be something to it! I don't think your issue is a lack of, or a stuck (but it could be stuck) tstat, I think you've got an air pocket or a mismatched set of heads/400 block. Pull the tstat housing and see if you have coolant to the top of the intake, if not top it up and try again. If it doesn't work (you could even throw in a new tstat while its apart) then I would pull the heads.

8Mike9

I know it's somewhat off topic to the thread, but think about what occurs when you "leave the coolant in the radiator longer". By doing that you also leave the coolant in the block longer, which in turn raises the coolant temperture.

T'stat isn't there to control the flowrate of the coolant, but to allow flow of the coolant when it raises to a setpoint.

86t/a owner

it might be a dumb thing but, your breaking in your cam right, your sitting there for a few min, rev between 2k and 2500, do you have a fan or anything in front to blow air on the rad? probley is not the problem but you should have that it might help.
Nathan

Sonix

iTrader: (1)

bang on, this is what you need to do.

86interceptor

I put 2 box fans in front of the car today, put a lower temp thermostat in, and fillled the block up while the thermo housing was off. it has blown that rubber plug under the top rad hose 2 times now after I turn the engine off when the temp rises . I leave the fan running. I am wondering if my rad might be to small?? it is the one that came in the car with the 305

damn thing keeps overheating. What do I do?

Rob Wade

How hot is it while its running?

86interceptor

I let it cool down to about 100 degrees before staarting back up and turn it off at 240 or maybe a little more
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sometimes it takes like 4 minutes to get the temp that high and sometimes it runs for like 8 before getting that hot

by the way the timing is set at 8 degrees below tdc

Rob Wade

Are you shuttung it off because the temp is still rising or because you want to shut it off. If its a fresh motor its not uncommon for it to run a little warm during cam break in. If its not a roller cam motor you really need to try and NOT shut it off until the cam is broken it (heat treat) which is usually 10-15 minutes at 2500-3000 rpm for a non roller. If the temp is high but not going higher I wouldn't be TOO concerned but if your shutting it off because its still rising you may have a problem. Did adding the coolant through the intake a new tstat make ANY diff. at all?

86interceptor

it made a small difference but not enough to matter. I know the heads came off a 400 sbc but I am wandering if the guy that built it put the steam holes in the head gaskets???? I had to shut it off because the temp kept climbing. I have run it at least 35 minutes on and off trying to keep it from over heating I am thinking of taking it down the road at about 2 grand to 2500 and see if it is over heating because of lack of air flow

rx7speed

I don't buy that one. I've seen it quite a few times without a thermostat your car actually runs a **** load colder.

86interceptor

I took it down the road and it stays around 200-220 as long as I am moving but it will still overheat if it is sitting and running. Is my original radiator big enough for this new 400sb???

86interceptor

well I drove it around for a while tonight and had no problems with overheating but it is kinda cool here at night so we will see tomorrow how it does

to everyone who replyed

AJB-283

Get the radiator checked. Look for a 4 core rad to help keep that 400 running cooler. They have a tentency to run hotter than a 305 or 350. My 383 runs warmer than the old 305 that I had in it. Just my thought on the matter!! Good luck and hope that you get it corrected!!

Rob Wade

Are you running a fan shroud. You need to have one on there to allow the fan to pull air THROUGH the rad, not around it.

vortech35091RS

Try replacing your radiator cap....You'd be supprised how many times I see cars comming in overheating like that and it was the damn radiator cap the whole time

roughskinjrz

whaddya do if the motor overheats while breaking in your cam? im about to break in my cam, its hydraulic flat tappet of course. i cant run it without the radiator cap on, n i heard its not good to shut it off during break in

Rob Wade

Its very critical that the motor runs for + or - 10 minutes on initial break in. What you are doing is heat treating the cam. Bringing the camshaft up to X temp for this amount of time and then letting it cool is a heat treating process that will harden the cam and set the lifters into a rotating cycle. The bottom of the lifters are concave and the cam convex to promote the rotation of the lifters so that the lifter will not drag across the top of the cam lobe. If the lifters don't turn before the cam is broken in you will wipe out a lobe. Read all the previous posts above re: filling intake (not rad) to the top, run a shroud, make sure you have addiquate air getting to the rad etc. You need to make sure the motor will not need to be shut off early. Even after you do all of these precautions.....its still a 50/50 crapshoot that the cam lives. Good luck.

roughskinjrz

im not runnning a 400 though just a 350, so the steam holes are not my business.

ill fill the intake thought the thermostat hole now instead of the radiator so i dont get any air pockets. thanks for that advice.

i dont think i should run into any other problems. hope not anyway.

Blazer79

Try Water Wetter also. Its an additive for your radiator.

86interceptor

I am putting dual fans on it tomorrow, but I have been driving it a little here and there and not having any more problems. I think I had the timing set wrong, the machine shop I called said to start the timing at 8degrees btdc but after having all these troubles with over heating, I called a buddy that has a 856hp blown mustang and he said that with my cam I needed to start at 15 degrees btdc and go from there and the motor really liked that. should I go even farther??

F-BIRD'88

With a big rough idle cam you eed all the initial timing it will take. I run mine with the mechanical advance locked out so initial timing is 36deg and total timing is 36deg. Or you can remove the distributor and modify the advance curve by shortening the mechanical travel. Stock is 20-24deg travel. You want to shorten that to about 10-12deg travel. that will allow 22-24 deg initial at idle and 34-36 at high rpm.

The EGR effect of a long duration cam that creates that " racy idle" also slows downt he fuel burn rate. so in order to burn the fuel instead of heating up the cylinder walls, your motor wants the increased timing at idle to run correctly and not over heat. Try it. Increase the timing to 24 deg at idle and reset the carb idle mixture and speed to get best idle at 750rpm. *WARNING* Do not drive the car like this until you have modified the distributor with limited advance travel or you will damage the motor from too much hi rpm advance.

A 305 rad will keep it cool only if it is in *perfect condition* {new} and you have a 7 blade GM mechanical fan (clutch fan) and proper fan shroud. A electric fan will not move enough air thru the rad. Get the clutch fan and shroud off a 85 camaro or firebird with a carbed 305. If the clutch is shot replace it.
Reduce the amount of antifreeze to water ratio (more water in the summer) too much antifreeze doesn't cool as good as water.
and add a bottle or two of Water Wetter. Drill a few 1-8" burp holes in your thermosstat.

you want about 24 deg at idle and 34 to 36 at high rpm max advance.
Then add 15 deg of vacuum advance (ported vacuum) For efficient cruising.
What cam are you using?