350 tbi running too cold

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

Slooptin

Full Access Member
Joined
Mar 6, 2017
Posts
153
Reaction score
89
Location
Denver
First Name
Vance
Truck Year
1985
Truck Model
k30
Engine Size
454
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
 

Slooptin

Full Access Member
Joined
Mar 6, 2017
Posts
153
Reaction score
89
Location
Denver
First Name
Vance
Truck Year
1985
Truck Model
k30
Engine Size
454
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

Full Access Member
Joined
Mar 18, 2017
Posts
4,208
Reaction score
8,079
Location
Arizona
First Name
Mike
Truck Year
85
Truck Model
K20
Engine Size
350
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

Full Access Member
Joined
May 27, 2018
Posts
1,223
Reaction score
1,305
Location
Kansas city
First Name
glen
Truck Year
1990
Truck Model
suburban 1500
Engine Size
350
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

Full Access Member
Joined
Dec 31, 2021
Posts
2,054
Reaction score
2,997
Location
Spokane, Washington
First Name
Brian
Truck Year
81,85
Truck Model
K20
Engine Size
350
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

Member
Joined
Nov 10, 2024
Posts
58
Reaction score
104
Location
vt
First Name
Joe
Truck Year
1977
Truck Model
c20
Engine Size
6.6
Are you reading the guage or the engine temp with a scan tool?
 

Slooptin

Full Access Member
Joined
Mar 6, 2017
Posts
153
Reaction score
89
Location
Denver
First Name
Vance
Truck Year
1985
Truck Model
k30
Engine Size
454
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
 

Attachments

  • IMG_4066.jpeg
    IMG_4066.jpeg
    74.5 KB · Views: 16

SquareRoot

Full Access Member
Joined
Mar 18, 2017
Posts
4,208
Reaction score
8,079
Location
Arizona
First Name
Mike
Truck Year
85
Truck Model
K20
Engine Size
350
Interesting. I have never seen a stat like that. I'm curious how it works and why it exists.
 

Slooptin

Full Access Member
Joined
Mar 6, 2017
Posts
153
Reaction score
89
Location
Denver
First Name
Vance
Truck Year
1985
Truck Model
k30
Engine Size
454
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

Full Access Member
Joined
Mar 19, 2018
Posts
4,044
Reaction score
6,637
Location
Houston, Texas
First Name
Britt
Truck Year
1980
Truck Model
GMC K1500 Suburban
Engine Size
350
Hopefully this link works- I just had a thought that this is a fail safe thermostat.

Maybe. :think:

 

SquareRoot

Full Access Member
Joined
Mar 18, 2017
Posts
4,208
Reaction score
8,079
Location
Arizona
First Name
Mike
Truck Year
85
Truck Model
K20
Engine Size
350
Hopefully this link works- I just had a thought that this is a fail safe thermostat.

Maybe. :think:

Interesting reviews.
 

Attachments

  • Screenshot_20241204-034519.png
    Screenshot_20241204-034519.png
    224.6 KB · Views: 5

Slooptin

Full Access Member
Joined
Mar 6, 2017
Posts
153
Reaction score
89
Location
Denver
First Name
Vance
Truck Year
1985
Truck Model
k30
Engine Size
454
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

Full Access Member
Joined
Jan 8, 2018
Posts
2,461
Reaction score
3,841
Location
Central Indiana
First Name
Matt
Truck Year
81
Truck Model
GMC 1/2 ton
Engine Size
455 Olds
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!!
 

Latest posts

Forum statistics

Threads
44,267
Posts
953,158
Members
36,458
Latest member
chemo
Top