Here's where I run my temp sensor for my EFI. Has proven to be a good location. 
Also that hose clamp looks a little tight....
Also that hose clamp looks a little tight....
CK5
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Engine will not maintain temps
- Thread starter PJ Walters
- Start date
That location will work.
Just getting caught up here, the main issues the engine gets to temp, t-stat opens and the fans come on and temps drop to 150-160?
The Holley system is controlling the fans right? Is that adjustable?
I agree that what others have pointed out on temp sensor position. But if the fans are kicking on at or near the t-stat rated temp the cooling system is going to not allow it to maintain temp.
Before going nuts moving sensors or changing the thermostat again I'd change the temps when the fans kick on and off at. Move the fan on setpoint to 210 and shut it off at 195.
The Holley system is controlling the fans right? Is that adjustable?
I agree that what others have pointed out on temp sensor position. But if the fans are kicking on at or near the t-stat rated temp the cooling system is going to not allow it to maintain temp.
Before going nuts moving sensors or changing the thermostat again I'd change the temps when the fans kick on and off at. Move the fan on setpoint to 210 and shut it off at 195.
PJ Walters
Registered Member
The fans never turn on. They only turn on at idle. The Sniper does control them.
The front of the intake/T stat housing will be the hottest part of the engine coolant wise. It's the last place before it hits the radiator to be cooled. Hopefully your harness will allow you to move the sensor fwd just a bit.
Also, is your 3 row radiator aluminum or brass? Aluminum gets rid of heat much faster, so much that a 3 row alum is as efficient as a 4 row brass. So if you had a 4 row brass to begin with and then put in a 3 row alum, you are right back where you started.
When I built my 400 I remember there was some sort of crossover port that went through the intake and could be blocked off or not. Had something to do with emissions. That's been awhile, but I vaguely remember it had to do with heat in the intake.
Not sure what your outside temps are where you're at, but you could block off part of the radiator, just for testing if moving the temp sensor doesn't work.
I saw your post on the rear seat. Very nice.
So they come on at idle and stay on? What is controlling them? Do you have them on a manual switch or they are on a thermostatic switch pulling it's own temp value off the radiator?
I went through this when I swapped in a 6.2/big block radiator in with my 5.3. The radiator was way more than the little 5.3 needed. It ran at 160 degrees pretty much in all but the hottest ambient temps. It didn't go past 190 on my gauge until it was over 100 degrees outside. It kept the ECM in cold enrichment mode. Other than using more fuel I didn't worry about it because it ran fine.
I saw and earlier post that suggested to kill the fans and see what the temp does. What was the result? Did it run warmer?
As high up as that is, I'm not sure how the sensor doesn't have air trapped under it. They need to be in coolant for accurate temperature readings. They don't do well with air temperature.
With full coolant, I'd take it loose until coolant seeps out, then snug it back down. Easy to see if that "fixes" it.
With full coolant, I'd take it loose until coolant seeps out, then snug it back down. Easy to see if that "fixes" it.
Look at Vortec 5.7's and TBI 454's as they both had a coolant temp sensor right by the thermostat. It's not unheard of to use that spot.
runnng
If there was a bubble there it would also effect the t-stat. I don't think it would be running cooler because of it.
Look at it this way, the engine is always going to produce heat when running. Once the t-stat opens that hot water goes to the radiator and will drop temp across it and go back in through the water pump. Its as basic a system can get. So what can cause the engine to run too cool? We know the engine is still producing heat, the t-stat is opening and obviously the radiator is doing it's job. So are the fans running all the time to never allow the coolant to maintain temp? Or is the radiator that much more efficient that its not maintaining the temp? Combo of both? If the temp drops that far below the rating of the t-stat you would think the t-stat would close again and allow the engine to come back up to temp again. A t-stat that opens and sticks open would give the same effect as the other two issues in that the engine never has time to build any heat up. It just constantly flows. Chances of getting 5 t-stats that stick open would be lottery level type odds. But are they hanging up in the housing?
I'm sure you got some of the used t-stats handy, it would be interesting to test one with a pot of boiling water to see if it opens and closes.
runnng
If there was a bubble there it would also effect the t-stat. I don't think it would be running cooler because of it.
Look at it this way, the engine is always going to produce heat when running. Once the t-stat opens that hot water goes to the radiator and will drop temp across it and go back in through the water pump. Its as basic a system can get. So what can cause the engine to run too cool? We know the engine is still producing heat, the t-stat is opening and obviously the radiator is doing it's job. So are the fans running all the time to never allow the coolant to maintain temp? Or is the radiator that much more efficient that its not maintaining the temp? Combo of both? If the temp drops that far below the rating of the t-stat you would think the t-stat would close again and allow the engine to come back up to temp again. A t-stat that opens and sticks open would give the same effect as the other two issues in that the engine never has time to build any heat up. It just constantly flows. Chances of getting 5 t-stats that stick open would be lottery level type odds. But are they hanging up in the housing?
I'm sure you got some of the used t-stats handy, it would be interesting to test one with a pot of boiling water to see if it opens and closes.
Ok, maybe I'm crazy, but there's a lot of focus on what the fans are doing when it seems like that shouldn't be a consideration with the engine running below tstat opening temps. Sending unit location seems to be the most plausible cause to me. I don't know what you've had a chance to do yet, but it seems to me like moving that sending unit to driver side cylinder head, as was already mentioned, might be the easiest way to see your true 'operating temps'. I'm saying that loosely because the numbers we're used to seeing and are comfortable with on sbc/bbc engines come from that stock sending unit location. As others have also said, temps vary from spot to spot.
Also, your engine bay is so clean. Looks great!
Also, your engine bay is so clean. Looks great!
I know the problem, you’re truck is too clean! Get some mud on that radiator and your overly cool temps will be taken care of.
From all that you have done so far, it is clear that many things can be ruled out. I would be interested moving the coolant sensor from the back of the manifold to either the front where the t stat is or in the head up towards the front of the engine. Those areas will be most hot and consistent with locations where GM originally put these sensors.
Lastly, make sure there is no air in the system (not usually a problem with small blocks but common with ls motors). Either crack the sensor to bleed air or leave the cap off with the engine running and cold until all bubbles leave the system. Also, get rid of that reducer on the sensor. I don’t remember offhand the exact bung sizes but obtain a sensor that doesn’t require that reducer. I don’t like the fact the reducer will pull the tip of the sensor out of the coolant path.
I have “cooling issues” as well. But I know what is going on. I have a 6.0 ls2 with a 4 row aluminum radiator and electric fans that run all the time. I need to get around to putting in a proper relay box and allow the FiTech computer to control the fans and my problem will be solved.
From all that you have done so far, it is clear that many things can be ruled out. I would be interested moving the coolant sensor from the back of the manifold to either the front where the t stat is or in the head up towards the front of the engine. Those areas will be most hot and consistent with locations where GM originally put these sensors.
Lastly, make sure there is no air in the system (not usually a problem with small blocks but common with ls motors). Either crack the sensor to bleed air or leave the cap off with the engine running and cold until all bubbles leave the system. Also, get rid of that reducer on the sensor. I don’t remember offhand the exact bung sizes but obtain a sensor that doesn’t require that reducer. I don’t like the fact the reducer will pull the tip of the sensor out of the coolant path.
I have “cooling issues” as well. But I know what is going on. I have a 6.0 ls2 with a 4 row aluminum radiator and electric fans that run all the time. I need to get around to putting in a proper relay box and allow the FiTech computer to control the fans and my problem will be solved.
Depending on cooling system efficiency, it's possible. I'd agree unlikely, but having seen my engine temp drop significantly below 195* under the right conditions, it isnt outside the realm of possibilities.
Having said that, and having now seen where and how the sensor is being utilized, I'm much more likely to believe the sensor isn't measuring coolant temp.
IIRC GM added the rear intake coolant crossover in some applications (and/or used the back of intake manifold heater core feed in other apps) later on because the coolant back there doesn't see much coolant flow, thus runs *hotter* than the rest of the engine.
My money is on bleeding that location of air fixing the problem. Front of intake or side of the head is normal for coolant temp measuring, but unless I was seeing ridiculously high temps back there, I'd not worry about shuffling the sensor around.
I don't see how that sensor location is getting any coolant flow. Even if it's burped of air, there won't be any flow past the sensor tip.
That intake looks like one for racing to even out the flow from the heads at higher rpm.
That intake looks like one for racing to even out the flow from the heads at higher rpm.
One other thing I was thinking about is regarding the restrictive plates in the intake gaskets. If I remember correctly gm put in those restrictor plates for the coolant passages for later model 350’s in an effort to run a little hotter, especially for the tbi systems as they run a little hotter compared to the carbs…Emissions and all that jazz.
are the restrictor plates still in? Are they in the rear coolant passages?
are the restrictor plates still in? Are they in the rear coolant passages?
Wait a sec. If the Holley system is controlling the fans I can understand any variation in reading will lend to an error of when the fans do kick in. Even with the sensor in it's current position why not go in and bump the on/off temps to higher be values? Sure would be easier than moving sensors.
bp71k5
3/4 ton status
I think the issue is that the fans aren’t coming on (except at idle) because the temp never reads above 160F. So raising the on/off temp which is already way above 160F wouldn’t do anything.
If the fans shouldn't be on until 195° why are they on at idle? That's the confusion here. Are they shutting off if the engine is revved over idle? Or are they on all the time?
I'm not really familiar with the Holley system so I don't know it like the factory stuff, but something still don't sound right. If the fans are on all the time there isn't any way the engine will have a chance to get any heat in it. It seems odd Holley would kick them on at an idle and shut them off above idle until the on temp value is reached.
I doubt coolant flow matters nearly as much as location. If it's in coolant, which is unknown at this point, it should be reading something at least near thermostat temp.I don't see how that sensor location is getting any coolant flow. Even if it's burped of air, there won't be any flow past the sensor tip.
That intake looks like one for racing to even out the flow from the heads at higher rpm.
The difference in how accurate and quickly the temp reading changes when a temp sensor is in fluid or air is beyond significant. Coolant conducts heat very well, which is why even with a closed t-stat the engine temp can be driven below the thermostats rated temp, and why I doubt location is a big deal. Yes, the temp will be different, I don't feel it will be significant.
If coolants ability to transfer heat wasn't so good, there would be no reason to cover the radiators on rigs in cold temps, as the thermostat SHOULD be able to maintain engine temp...but the coolant still conducts enough heat to effectively cool the engine with minimal coolant flow.
bp71k5
3/4 ton status
Agreed, there’s something odd about the fans being on at idle.
Sorry, but it will make a difference. If the coolant can't flow past it, how will it tell when the system gets hot?
Coolant must flow to do it's job, and monitoring stagnant coolant isn't going to work. Same as if the bushing holds it out too far, but more pronounced.
Yes, location will make a difference in how much flow goes past the sensor.
I looked back at the OP sensor adapter. I am pretty sure you can get an adapter that will allow that sensor to mount flush with the intake. Pretty sure Ace hardware or Homeless Depot has a brass adapter that goes flush. This would eliminate any air pocket and put the sensor right into the coolant flow to get an accurate reading. I still think that moving the sensor to the front of the intake near the T stat housing would be best, combined with the flush mount adapter. That 383 should be putting out plenty of heat otherwise.
