Will Not Reach Normal Operating Temperature

[jswiftsr]

I saw the compression test and wondered if the throttle plates were held open for it. 128-135 is pretty low. All plugs out, throttle open, take the compression reading on the third revolution on each cylinder. Just asking if that's about how it was done.

How long was it run pig rich? Possible you washed the rings?

Yes, engine cold (about 54 degrees that day). WOT 4 turns per cylinder. This engine has about 30K on it since build. I took the guy a "W" Tonwanda engine and he dumped a I'm guessing a rebuilt block with all the numbers off of it...and the counter balancer had a sleeve bearing in the rear instead of a ball bearing like I took him. He stole my motor, and I have been trying to figure this engine problem out off and on since 2011.

Frankly, I think somehow it running rich, is the problem with it not getting hot enough. (Richer mix = cooler combustion / Leaner mix = hotter combustion). I am putting together a computer to check the data with to see what it looks like.

 

[Frank Enstein]

My wife's Astro did this to us a month ago. Six month old T-stat stuck open. GET a BRA-330-195 from Summit Racing. Not made in China. Fixed it right up. This is the required type for high flow water pumps.

 

[Hipster]

Yes, engine cold (about 54 degrees that day). WOT 4 turns per cylinder. This engine has about 30K on it since build. I took the guy a "W" Tonwanda engine and he dumped a I'm guessing a rebuilt block with all the numbers off of it...and the counter balancer had a sleeve bearing in the rear instead of a ball bearing like I took him. He stole my motor, and I have been trying to figure this engine problem out off and on since 2011.

Frankly, I think somehow it running rich, is the problem with it not getting hot enough. (Richer mix = cooler combustion / Leaner mix = hotter combustion). I am putting together a computer to check the data with to see what it looks like.

You skipped over, throttle plates open? That will make a big difference on a compression test.

Poor compression will make for a poor and incomplete combustion event that doesn't generate the same amount of heat. I don't know what stock specs for that engine are but 128-32psi is like an 8.5:1cr engine with just about shot out rings when you're using stockish cam intake valve closing events. Most stock stuff is usually in the 160ish + psi range.

I would imagine with the soot you mentioned the plugs are sooty. You need 8 new ones before you end up back feeding the spark energy to the ICM and kill it but you should know this because you already have all the answers.

 

[Carlaisle]

I chased a similar problem on a different engine for years. It was the thermostat. I got 2 brand new ones in a row that tested good but were bad. Was also sold a water pump in the process that pumped water but somehow caused the engine to overheat even at idle.

 

[stutaeng]

I did a compression test on my 99 4.3 Silverado a few years back and got numbers similar to yours. I did have a no heat symptom once in the winter and it was the thermostat. Doubt those compression numbers are giving the low engine temperature problems.

I was going to suggest hooking up a scanner to see if the coolant temperature is actually low. The dash cluster guage is not accurate on some models. Not sure why.

I would test your thermostat. Dunk it in a old pot and put on the stove.

I was chasing my tail on my 5.7 that only read halfway mark on dash. I changed the temp sender on the driver side head, but got a wrong one at the parts store, then engine overheated! Went down the rabbit hole thinking I had air in my system. Someone here mention that the new sender looked different. And sure enough it was the wrong one.

Checked the thermostat as I mentioned and it opened right before water began boiling. 190 or 195F unit. Basically, all for nothing and gave up on it...

Put the right sender, and guage still only shows 1/4 mark, but the ECU does say 190F when I hook up my scanner.

Check that you have no blocks for coolant flow as well. Removing the radiator hose briefly and you should have flow. But if you didn't have flow, the engine would actually overheat.


My buddy has a 77 F150 that has not figured out why it overheats. Basically has checked/ changed everything has been mentioned by everyone here, but has the opposite of what you have. But I have not messed with his truck.

 

[454cid]

I put a temp Probe with my fluke digital meter in the radiator. I also tested it at the tstat neck and the heater hoses with an IR Thermometer. they all matched the temp gauge, 155 degrees. I have little heat blowing through the vents, with heat on. But a blend door is key to heat in the vehicle, but irrelevant to engine temp.

Ok, that's good to know. I'd try covering the radiator until you get heat. If you can get heat that way, then I'd suspect over-cooling. You mentioned buying three thermostats, one being GM. I have no idea who is actually making them, but I've heard of quite a few thermostats (in general) being bad. Do you happen to have an old one laying around that worked? ...sometimes, people replace that kind of thing before actually waiting until it goes bad.

Here's a couple more possibilities.... I looked the parts up online. Your thermostat is kind of short, are you possibly installing it upside down...meaning the spring towards the radiator? The pressure from the pump may not be allowing it to close. Another thing, which gasket are you using? It looks like the rubber gasket and the beaded paper are available for your year. If you're using a thermostat with the rubber gasket, in a manifold made for the paper, I believe you'll have coolant going right around.

 

[jswiftsr]

You skipped over, throttle plates open? That will make a big difference on a compression test.

Poor compression will make for a poor and incomplete combustion event that doesn't generate the same amount of heat. I don't know what stock specs for that engine are but 128-32psi is like an 8.5:1cr engine with just about shot out rings when you're using stockish cam intake valve closing events. Most stock stuff is usually in the 160ish + psi range.

I would imagine with the soot you mentioned the plugs are sooty. You need 8 new ones before you end up back feeding the spark energy to the ICM and kill it but you should know this because you already have all the answers.

WOT= Wide Open Throttle. Compression readings were 128-135. The soot was from a defective O2 sensor I replaced. though I think it could still be running a lil rich. I did replace all 6 plugs with Iridium, new cap and rotor with a new wire set.

 

[jswiftsr]

Ok, that's good to know. I'd try covering the radiator until you get heat. If you can get heat that way, then I'd suspect over-cooling. You mentioned buying three thermostats, one being GM. I have no idea who is actually making them, but I've heard of quite a few thermostats (in general) being bad. Do you happen to have an old one laying around that worked? ...sometimes, people replace that kind of thing before actually waiting until it goes bad.

Here's a couple more possibilities.... I looked the parts up online. Your thermostat is kind of short, are you possibly installing it upside down...meaning the spring towards the radiator? The pressure from the pump may not be allowing it to close. Another thing, which gasket are you using? It looks like the rubber gasket and the beaded paper are available for your year. If you're using a thermostat with the rubber gasket, in a manifold made for the paper, I believe you'll have coolant going right around.

I did try 3 thermostats....2 Stants and the last one came from GM. The thermostat is installed with spring toward the manifold. Both rubber and paper gaskets used. I once thought the paper being in there that the thermostat might have came loose and allowed water around the edge of the rubber seal, but when I took it loose to change it, the thermostat was still secure in the intake with it's rubber gasket.

 

[454cid]

I did try 3 thermostats....2 Stants and the last one came from GM.

Right, I saw that..... but you're still over cooling the engine. So do you have an old thermostat that was known to work when it was removed? If so try that one.

The thermostat is installed with spring toward the manifold.

Ok, good.

Both rubber and paper gaskets used. I once thought the paper being in there that the thermostat might have came loose and allowed water around the edge of the rubber seal, but when I took it loose to change it, the thermostat was still secure in the intake with it's rubber gasket.

Both? I'm not certain about the V6, but my 454 only uses the rubber o-ring gasket. The rubber replaced the paper. I suppose the V6 could be different, and I wouldn't think both would over cool any way since the thermostat is still secured by the rubber.

How have you been running the engine to check things out.... just idling in the drive way? short trips? longer trips? What are you using for coolant.... pre-mix? 50/50 that you mixed yourself? Some other ratio?

 

[jswiftsr]

Right, I saw that..... but you're still over cooling the engine. So do you have an old thermostat that was known to work when it was removed? If so try that one.



Ok, good.



Both? I'm not certain about the V6, but my 454 only uses the rubber o-ring gasket. The rubber replaced the paper. I suppose the V6 could be different, and I wouldn't think both would over cool any way since the thermostat is still secured by the rubber.

How have you been running the engine to check things out.... just idling in the drive way? short trips? longer trips? What are you using for coolant.... pre-mix? 50/50 that you mixed yourself? Some other ratio?

Don't have another old thermostat as I know of. Been driving it at work. Using Dexcool that I mix myself (50/50) with distilled water. I was thinking of maybe pulling the thermostat again.....installing another new thermostat, and just using the rubber seal in the intake. What sealant do you use without a gasket? Red RTV?

By the way, the 92-95 Astro "W" 4.3 non-vortec is different than 96 up Astros and Pickups. I dont think 96 and up uses sealer on the flange. I think it seals against the rubber gasket on the thermostat. The rubber gasket on the 92-95 is like a bevel o-ring around the outside. That is why I thought the paper gasket was also necessary. Comments welcome.