350 tbi running too cold

Slooptin · Nov 26, 2024

Since everyone's been helpful with my big block issue, i figured maybe someone knows what's going on with my small block. TBI 350 in my suburban, 195 degree thermostat and a new spectra CU730 radiator (19" tall with a 2-1/8" thick core). The replacement radiator matched what I took out which cooled the truck more than it needed before, but now it works too well. truck sits at ~170 degrees after the t stat opens and after taking it on the highway a couple of times, the CEL comes on after I hit 55 mph. From what I can tell, this is because the ecu needs to see higher temps to lean out the mixture and open the egr valve.

Would going to a radiator with a thinner 1-1/4" core (like this one https://www.rockauto.com/en/moreinfo.php?pk=272020&cc=1301465&pt=2172&jsn=1435) bring the temps up? In the meantime, I'm probably going to stick some cardboard in front of my rad to see if that will get me through winter

SquareRoot · Nov 26, 2024

If its running less than 195 with a 195 stat, the stat is bad, the sending unit is bad or your gauge is defective.

Slooptin · Nov 26, 2024

SquareRoot said:
If its running less than 195 with a 195 stat, the stat is bad, the sending unit is bad or your gauge is defective.

So even if I can watch the temp climb to 210 or a little past on cold start then basically drop down to 170, its a bad t stat?

SquareRoot · Nov 26, 2024

Assuming your gauge is accurate, I'd say yes. Sounds like its hanging in the open position. It should open and close within 10 degrees of it's rating. I had this happen last winter with similar symptoms and my EFI wouldn't go into closed loop. Turned out the rubber gasket on the radiator cap deteriorated and a piece of rubber was floating around the coolant and got stuck in the stat. I would pull it out, check it and check its operation in a pan of hot water on the stove. That will rule it out.

gmbellew · Nov 26, 2024

my 350tbi burb runs at 195-200 when it is cool outside and 195-210 when it is warm outside and depending on engine load. but my gauge isn't accurate. it reads on the 2nd hash at 195deg engine temp. it is pretty close to 210 when the gauge reads 210. I monitor CTS with ALDLDroid, so I know what the temp is at the t stat.

my tstat is a little lazy opening. temps on the gauge approach 210 or a little higher before it opens all the way on a cold start. subsequent starts while engine sort of warm it doesn't swing so high before the t Stat opens up.

as far as I know, if the engine is cold, it won't set a engine light. I'd pull codes. but one of the things it tests for in the highway is EGR operation.

fast 99 · Nov 26, 2024

Also keep in mind where the sender is. If in head it will read about 10 degrees hotter than near the stat in the intake.

Really cheap to diagnose and a very handy tool to have. Go to HF and buy a temperature gun. Run vehicle a while, check stat housing.

When I bought mine it was $250 now HF has them for 11 bucks, just looked. For that money everyone should have one.

77Dmax · Nov 26, 2024

Are you reading the guage or the engine temp with a scan tool?

Slooptin · Nov 26, 2024

So this was the t stat that was in there. Looks like there are tabs on the side to “lock” it open once it opens which probably explains the issue. New t stat seems to be working but still oscillating between ~175 and 195. Better than before but still thinking the radiator is working too well

SquareRoot · Dec 3, 2024

Interesting. I have never seen a stat like that. I'm curious how it works and why it exists.

Slooptin · Dec 3, 2024

SquareRoot said:
Interesting. I have never seen a stat like that. I'm curious how it works and why it exists.

It looks like those tabs lock the stat open once it hits the set temp. I'm assuming they open up when the truck fully cools down to let the stat close. No clue as to what the reason was for it or why it was there

Goldie Driver · Dec 4, 2024

Hopefully this link works- I just had a thought that this is a fail safe thermostat.

Maybe. :think:

Failsafe Thermostat 7200-180

Shop for Failsafe Thermostat 7200-180 with confidence at AutoZone.com. Parts are just part of what we do. Get yours online today and pick up in store.

www.autozone.com

SquareRoot · Dec 4, 2024

Goldie Driver said:
Hopefully this link works- I just had a thought that this is a fail safe thermostat.

Maybe.

Failsafe Thermostat 7200-180

Shop for Failsafe Thermostat 7200-180 with confidence at AutoZone.com. Parts are just part of what we do. Get yours online today and pick up in store.

www.autozone.com

Interesting reviews.

Slooptin · Dec 4, 2024

Good to know. I looked them up and its nothing but negative reviews and people saying to toss it in the trash. guess I'll follow suit

Matt69olds · Dec 4, 2024

I put a piece of cardboard between the radiator and condenser on my Ram. The diesel engines hold almost 7 gallons of coolant if I remember correctly, it takes a LONG time to heat up, and when it’s really cold the temp cycles as you describe.

Block off about half of the radiator, see what happens. Just don’t forget the cardboard on the first warm day!!

Slooptin · Dec 6, 2024

Thats my plan if the thinner core rad doesn't work out. Hoping the 1-1/4" core will lower the coolant volume a little and reduce cooling capacity to help keep temps in the 190-200 range. I never thought I'd be dealing with an engine running too cold lol

350 tbi running too cold

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