Just built 355 overheating!

[redneck_reed78]

Want to pick y'all's brains. Just got my fresh 355 in the rig and broke in. It has a rebuilt/modified TBI unit and vortec fuel pump to support the power bump from the vortec heads, mild cam (SUM-K1102), headers etc. Ever since during break in process, I can't keep this engine cool. It will sit and idle for a while creep up. And when driving it, I can't get more than a mile before it gets to 220F+ and I have to shut it down. Even with no thermostat it gets too hot. Also worth noting that it is real sluggish when driving and occasionally surges. I've played with the timing and it seems to run best setting at about 10 deg. Advance at idle. I haven't had a chip burned yet but I don't think it would cause this many problems. Have also tried different radiators and checked that the water pump is working, fan is fine... Everything cooling related was fine with the old motor as well. So I'm thinking i have it narrowed down to intake or head gaskets? If anyone has any input I'd appreciate it.

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[Vbb199]

This modified tbi unit... If you mean a Chevy 87-91, it's gonna be putting out 12-15, internal fuel pressure regulation unless you modified that.

With vortec heads, I'd imagine you need a high cfm, so would it be safe to assume you're running lean?

You can put a 120 psi behind that tbi and it'll still regulate it to the 12 or so psi.

What's your spark plugs look like after running it for a bit?

 

[redneck_reed78]

It's upgraded to a 18 psi regulator. Haven't pulled plugs again yet. If it's lean, would having a custom chip burned potentially be a fix?

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[Vbb199]

That is somewhat beyond my knowledge, but I do know when you go changing heads and such like that you can go to https://harristuning.com/product/custom-tbi-chip/
He'll set you up
And you fill out his form here:
https://harristuning.com/Tbi/custom-tuning-form/

 

[Vbb199]

A factory chip only sprays fuel, meters idle, and everything else off of a STOCK configuration.
Youve changed bore size, the throttle body, heads, etc.

Definitely would look into that.

Not saying "this will fix all your troubles"

But things like map, CTS, IAC, and O2 readings all change now with this different configuration of a motor vs a stock tbi

 

[redneck_reed78]

Yes a ton of knowledge on there I just sent him a email

 

[Frankenchevy]

Did you pay close attention to the heater hoses and bypass for the water pump/manifold? Vortec heads have to be routed a specific way.

Where is your temp sensor installed? Is the cooling system sealed so it can build pressure?

edit: I see you have thermostat pulled, so it shouldn’t be a bypass issue. It does sound like you have a coolant passage blocked somewhere by an incorrect gasket or something else funky. You’re sure all the air is purged, right?

 

[Wumbo]

How about water pump. Normal water pump w reverse rotation serpentine set up maybe?

 

[JoeR Jr]

I'm with Frankenchevy. The first place I'd try would be to vacuum bleed it and then check my gaskets to make sure I had coolant flow. Lean mixtures won't cause your troubles.
Joe

 

[QBuff02]

pictures. pictures of engine bay and engine layout. Bet a buck we can figure it out based solely off of pictures. lol

 

[QBuff02]

I'd also note that getting hot and being "real sluggish" is a lot of times symptoms of timing being way too far advanced. The engine is fighting itself to run IF it is too far advanced and it will create tons of heat and eventually take out head gaskets or worse. Did you change balancer or timing cover when engine was rebuilt? If all else is good as you stated, making sure cooling system has no air in it, and is not dead heading itself somewhere in the system and then timing or too lean would be where i'd start.

 

[MrMarty51]

Intake manifold gaskets was installed backwards.

 

[DoubleDingo]

No shroud? Fan clutch not working properly? Wrong temperature sending unit, or faulty sending unit?

 

[DoubleDingo]

I run vortec heads on my '81 and can sit and idle in triple digit temps and never overheat. Perhaps boring the cylinders got them a tad too thin? My engine is stock bore, so there's that.

 

[redneck_reed78]

Wow appreciate the responses! Got to look at it some more today, I think after a lot of tweaking I figured this out: Electronic advance doesn't seem to be working right. I set base timing at 5 degrees advance, then plugged the wire back in, which brings it to about 18 advance at idle. Revving up to 3000 RPM only bumps it to about 25 degrees. That might explain why it's doggy when driving or trying to accelerate; its too retarded. Set the base timing at about 15 degrees and plugged it in, yeilding around 30-32 degrees at 3k RPM. Drove it around like this and while it's not great it's noticably better. So I need to figure out why it's not advancing on its own now.

Talked to the engine builder and we agreed that the timing issue probably contributing to the heat problems. With NO thermostat in it, driving it around a few mins, never got over 140-160. Idling it still crept up to 210 but never above it. Rigging up an electric fan kept it managed even better. So I think the original radiator and 3 blade clutch fan are just not going to be adequate since I have more motor now.

Bottom line, I'm hoping that I just panicked and assumed the worse in the OP.

So if anyone has insight on what the advancing issue is or what are some good cooling upgrades, let me know. Thanks!