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TBI Running Hot

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pseudomike

1/2 ton status
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May 11, 2007
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Location
MA
Ok guys, I got a cooling issue that is giving me fits. The motor is a 1991 TBI (jasper reman ~20k mi), cammed (EDL-2102), has a Edelbrock performer TBI intake w/proper chip, stock manifolds new exhaust all the way back. The timing is balls on.

The issue I have is that the temp gage burries out before the thermostat opens...it is definitely way too hot not just a bad gage. I have tried multiple things to alleviate this. Thus far... the radiator is new 4 core copper, new heater core, I have changed the T-stat about 8 times Stant and DELCO all sorts of different heat ranges, new temp sensors both sides of the block (tried both heads), swapped a couple different water pumps currently running an aluminum high flow (yes it is reverse rot). I have not messed with the fan, it is stock, but it is definitely pulling serious air and the shroud is in place. When the T-stat opens the temp drops in like 5 seconds to ~150deg then cylces fine from there. Right now I am running it with a small (1/8") hole drilled in the thermostat to let water by before it opens and it seems to work (doesn't burry gage before opening) though it cycles between 195-220deg with a 195 t-stat. Intuition tells me something is wrong. I have drained and flushed the sytem a couple times and everything looks good. I don't see any air in the coolant or other contamination that would indicate a head gasket or mechanical problem nor is there any coolant in the oil, nor does it seem to burn any. It is not losing coolant, the system definitely holds pressure. I am kinda at hits end with it and my presumption is that there is a mechanical issue of some sort in the block IE craked head, head gasket, incorrect intake gaskets??? If anyone has some ideas shoot them my way. Thanks in advance.
 
It doesn't sound to me like you have any problem. With a 195 t-stat the temp should stay close to 195 give or take a little. Yours may be running a little on the high side at 220 but how much coolant are you running versus water? Coolant is thicker than water and is not very good for heat disapation. I like to use 1.5 gallons of coolant and the rest water. Since you're in Ma i would maybe go 2 gallons of coolant and then the rest water. Too much coolant can make it run hotter.
 
It's running about 60% water to coolant. I'm not as concerned about the temperature it is currently running. The issue is that I had to drill a hole in thermostat so it won't blow the radiator cap before the thermostat opens.
 
I drill an 1/8" hole in every t-stat i install that doesn't already have one. The 1/8" hole helps tremendously in eliminating air pockets when you have to drain the coolant for any reason.

What brand of water pump are you running and do you have a part number for it? I've never seen an aluminum reverse rotation water pump available before.
 
Well, perhaps it is normal operation then. It just seems odd that it will literally blow the radiator cap open without modifying the thermostat. I guess I will run it as is for now but I plan to monitor it closely. I did not have this trouble before the motor was rebuilt so it seems fishy. I drove the truck to work today and ran it about 80mph 3000rpm for 45 miles and it stayed right around 215deg.
 
It sounds fishy to me...personal experience has been that as long as the thermostat works, stock setup, (no hole or anything) the temp stays right at 195* as long as the vehicle is moving, and when the fan comes on at idle, it drops the temp down to what I have the temp set to.

You aren't overheating at 220* of course. Is this while you are moving or only at idle? If it's at idle ONLY, then to me it would point towards the fan. (I know you said it is moving air, just reasoning this out) If it stays at the t-stat temp at cruise, then the thermostat is working right.
 
With the hole drilled in the thermostat it will idle under 210 all day long. It runs 220 on the highway...but keep in mind it is about 20deg out today. What is going to happen in August?

Without a hole in the t-stat it will blow the radiator cap even if you just let it idle up to temperature. It simply can't be right...why would a DELCO stat come without a hole if it would blow the rad cap otherwise. Like I said...something fishy. A hole in the thermostat seems like a bandage to me.
 
I rember reading someone was having the same porblem as you with a TBI motor.
They fixed it by swapping the heater hoses around. The heater core was hooked up backward.
The Hose from the radiator goes to the top connection on the heater core.
The bottom hose goes to the manifold. TBI 350
 
Again, agreed. It should run right at rated temp on the freeway, hole or no. That should have no bearing on the fan, so something else is up.

If you run with no t-stat, does it ever warm up? I know results vary on this, IME a missing t-stat always results in overcooling. But you mention Delco, and apparently you can't get any better than that for t-stats in initial quality. :(
 
Aren't the heater hoses different sizes? I'm pretty sure mine are.

But, the heater hoses are hooked up "stock"?
 
W/o a thermostat it will run just about zero on the gage. Take it down the highway and will edge up a little. The core hose to the radiator is 3/4", maniold/blockis 5/8". I'm fairly sure they are ok (have to check for 100%) because the hose to the block is the stock one with the threads into the manifold, and being the smaller of the two it wouldn't fit in the incorrect position.
 
Can you post a picture of how the hoses hook up? If this started right after the rebuild, I always suspect installer error when I'm the installer.
 
The cooling system otherwise seems to be working correctly...removing one component and the problem disappears usually points to one issue.

Is your radiator cap working correctly?
 
I tried two different caps, both Stant 16lb.

I agree with the installer issue...my worry is that the issue is something installed incorrectly internal side of the motor. I will get a pic of the hoses tonight.
 
removing one component and the problem disappears usually points to one issue.
Click to expand...

Good point. Is the tstat installed upside down perhaps? I can't believe 8 different ones could be bad.
 
You know, I had that thought myself. I put the spring side down into the manifold...I'm a moron if that is incorrect?
 
I seriously doubt you hooked the hoses up wrong. It's odd that it heats up only on start up but then runs fine. I would swap in a 180* t stat with that set up though. I would swap the t stat and put the truck on a incline so the radiator cap is will above the engine and start it up without the radiator cap on and let it warm up. Be carefull when doing it but after it warms up put the cap back on before shutting the engine off. If there is a air pocket in it that should halp to get it out. Once that is done let it cool and see what happens when you start it up normally when cold. If it still heats up let it cool down again and stick a fan in front of the rad and start it up with air blowing over the rad. There is no reason that you should need to drill a hole in the t stat.
 
I had it all the way down to a 160deg stat....same problem. I'll try the incline trick and see what happens.
 
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