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SB400 running hot

babyburb

babyburb

1/2 ton status
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1H North of Dallas
I have read on here several times about the sb 400 motors running hot. My question is just how hot can they run without damage? I went out Friday night and basically rolled through a bunch of mud holes and only had to gas it in 1 and my temp gauge went all the way up to the line before the red. It never went over the line but is this running it to hot?

Not really wanting to spend any money on it with the 454 swap coming up. Just wondering in case I need to run it before then.
 
They shouldn't run any hotter than the thermostat temp, unless part of the cooling system is bad. Did you pack the radiator with mud and gunk while going through the mudholes? I see this a lot on trail rides.
 
This is common on 400's. Get a high volume water pump from summit. This helped out a lot on mine. A lower temp thermostat might help too.
 
I had the same thing happen a while back romping in the sand. Didn't watch the temp gauge until I was finished but shouldn't be filled with mud. I drained the rad not to long ago after I busted a hose and it was pretty clean. I used all new fluids though.

With normal driving or even pulling loads I never had a prob. Just slow moving, and then heavy throttle useage I guess. Would it be alright to run it with it right on the line? Or let it cool between holes. I have had to pull out 7 or so vehicles from sand and mud over the last month and I will probably have to pull more since every knows I have the winch now. I am going to have to start charging for gas at this point:D .
 
This motor didn't even have a thermosat when I first bought it. It ran fine but never really warmed up to normal temps until I installed one. Might be why they did without it I guess. Seems like that would only be a temporary fix in my opinion.
 
Yes, outside of performance reasons, a colder or no t-stat is a band-aid.

Certainly do a good visual, make sure the fins aren't all plugged up or covered with debris.

How is your engine fan? If it's not working, low speed, high load conditions will show higher temps quickly. You'd also likely notice a fan problem while say, climbing a hill at low engine RPM's. But sounds like you aren't or *weren't*.

What kind of thermostat are you running? Might not be working right, aftermarkets are pretty notorious for being bad often right out of the box. How are your cooling hoses? They can collapse and block coolant flow.

With it not doing it under load, and the quick spike in one particular situation, I'd not suspect the radiator internally. However visual inspection of a radiator is unfortunately worthless. Sediment settles, and the lower portion is the first to go bad, both because of that and corrosion. You can't fix it, and you can't see it. Flow testing is the only way to know if it's up to spec, and I'm not sure how many places can test it. I know one local to me can.

BTDT, radiator looked like new from looking down the cap area, plugged solid further down, about 50% of what it should have been flowing. But in that case, the engine overheated at idle and the heat was unmanageable.
 
Not sure of what thermostat it was. I paid like $5 for at Autozone. I guess I will check in on a colder one, replace it, and go find a mud hole! Good excuse for going to play, right? "Honey, I gotta go check and see if this new part on the burb works! I will be back in an hour or two!"
 
I dont know why, but nobody seemed to post up about the steam holes in the heads, if this motor has been gone through before and someone put heads on without the steam holes in them, theres your problem right there.... Nate
 
exactly those steam holes need to be put into the head in order for the coolant to flow through the block and heads or else that thing will heat up like crazy i blew my 400sb and i found out later the engine never had that done to it that was part of the problem
 
Spend some money on a temp gauge first, to find out if you even have a problem.:doah:

If that spot on your gauge is only 210, then your doing ok.

But you need to get the facts first before you spend time and energy fixing something that may not be broke.:D

And think again about that thermostat idea. All it basicly does is hold the coolant in the engine untill it warms up.
Once its over the stats temp, the stat stays open, so a colder one won't help.

It really sounds like everything is working properly and only gets warm when your working the engine pretty hard. And you actually may just need to take a little break like you suggest.

good luck
 
You might as well install a larger radiator if you're planning on a BBC down the road. Usaully 400s overheat from not enough flow or lack of radiator. The stock radiator might be too small and showing its age. Get the taller 4 core radiator. I found out the hard way that the stock radiator wasn't enough to keep my 454 cool enough.
 
if your worried about a hot 400 and a your swapping in a 454, your going to need a NEW cooling system or a very good one. due to the water jackets being so close to the cylinders in the 454's its hard to keep it cool. my 454 (.60 over) runs at about 210 all the time and you can tell it needs to be cooler, only thing is i can't get it any cooler with my 4 core radiator. soon i will be swaping a 6 core custom radiator and a new 7 blade flex fan made for big radiators. a victor series water pump may also be in store to complete the cooling system.

this just goes to show that you may have some problems cooling your BBC so you might as well do the most you can now and just do a cooling system flush when you put the beast BBC in.
 
400's are finicky. But, as long as you stay under 220* you'll be fine.
 
excellent info guys, (like always) What kind of radiator and where do I look for it at to find a 6 core? Is this only aftermarket type stuff or could I find one at a local bone yard in a newer model?
 
Wider and thinner is better if the materials are right. You'd need a very well designed radiator to actually be efficient with 6 cores, the coolant capacity alone is probably why they are even made that large. You are dealing with compromises with radiators...how large will fit, at what point is size not helping further, how efficient is the radiator design, etc.

Diesel radiators are the widest you'll find in these trucks.

Apparently a copper tubed radiator will be more efficient than aluminum, *all else equal*. But what I don't know is, are radiator tubes copper? I believe they are, and the brass in "copper/brass radiator" comes from the brass solder?

Not meaning to get off on a tangent here, the real answer is: whatever is most efficient, best built, in your price range, is what you should get. There is plenty of info out there to make an informed decision. :)
 
dyeager535 said:
Wider and thinner is better if the materials are right. You'd need a very well designed radiator to actually be efficient with 6 cores, the coolant capacity alone is probably why they are even made that large. You are dealing with compromises with radiators...how large will fit, at what point is size not helping further, how efficient is the radiator design, etc.
Click to expand...

yeah i have no idea where my radiator came from. my neighbor had it built for a 396 that was pulling a fifth wheel. he passed away many years ago and we ended up with it (thank goodness). i was suprised on the construction of the 6 cores in the radiator, they where staggerd so most all of the cores got air flow.
 
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