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Topic Review (Newest First)
02-11-2013 06:29 PM
Originally Posted by pickenspilot View Post
Sounds like you have a high bypass thermostat. Majority of coolant does not go thru the thermostat.
3 year old thread, he probably fixed it by now
02-11-2013 06:06 PM
pickenspilot Sounds like you have a high bypass thermostat. Majority of coolant does not go thru the thermostat.
01-08-2008 07:25 PM
Jmark Thanks for posting back and letting us know. Wow, 3 bad in a row, but it does happen. Maybe Juan was having a bad day on the assembly line! LOL

01-08-2008 07:21 PM

Well, after much head scratching and shoulder shrugging, I have my answer. I ran out, picked up a laser temp gauge to put a temp on the block after running 45 minutes in traffic. Gauge in Truck shows 105. Grounded the wire to the block, shows pegged hot...not a gauge or wiring problem...thank goodness! (I hate electrical probs!) Point the laser at the cylinder head...low and behold, 193*. Okay...Thermostat is working dead on. I ran hard, and I ran normal. Floored it, left plenty of tire behind, and also tried to drive very conservatively. Laser shows the same +/- 4*. Okay...Here I am thinking that I got a bad batch of thermostats, and now my thinking is that after three new sending units...all same store...I actually had a bad batch of sending units. I go to different store, try a different brand, change out the TSU, and Voila...Gauge in the truck shows exactly the same as the on. Rises up about 10 degrees if I drive hard, and comes right back down. I probably could have told by the temp coming out of the vents...but just to make things difficult, well, the blower switch went out just before this happened, and I just don't feel like taking the dash apart yet to fix it! So...I appologize for racking everyone elses brains and all, but who would have ever thought! No me, obviously. Thanks though for all the great advise, there is no doubt about the knowledge base here. Have a great time with your projects, and look back to this post soon. (This week) I will post a link to a youtube video with this neck snapping 84 chevy! Long Live Bowties!
01-08-2008 06:43 PM
Jmark Here is a good thread from some time back on thermostats.

clicky here..........

01-08-2008 05:54 PM
randywr Hey, Ive have experienced the same problem before. Your thermostat is too cold. The way it works is simple. With a cold thermostat, its gonna open early, letting cold water back into the block. I think that the radiator is cooling the water too much, hence cold temps. The problem can actually go to the opposite extremety too. If you put a good load on the engine and run the hell out of it, you'll more than likely over heat. This is also caused by too cold of a thermostat. The water was not staying in the radiator long enough to cool enough before the thermosat opend again, causing overheating. I just had to experiment with mine until i found the "happy-medium" to make it work correctly. I think it was a 190, but every set-up will behave a little differently. Cooling systems sound easy, but thats not always the case. Hope my similar experience helped. Good luck buddy.
01-08-2008 05:26 PM
PatM You are running an electric temp gauge. If I recall a dead short will peg the gauge on the hot side, and an open circuit will leave the gauge showing cold. Since your reading cool, it could be that you have either a bad wire running from the gage to the sender, or a bad power supply from the ign to the gauge. Your gauge also has a reference ground that can be contributing to problems. My guess is that both stats are OK, your engine is over-cooling maybe just a tad, and that the dramatic changes you are seeing are the result of an intermittent electrical problem in the gauge's wiring. I think I'd put a meter on the ign post of the gauge, with it wired and running, and check voltage to chassis ground.

Doc Vette -- We miss you?

01-08-2008 05:04 PM

I matter how much cooling power your radiator and water pump have, no cool water should flow if the therm is working properly. That's why I was so baffled. Like I said, I only changed the rad because this was running very warm on a 180 therm in 40 degree weather, at 55mph. And with Georgia summers, I wasn't going to wait to see what would happen in July! What killed me was that one day it worked just fine, and the next it wouldn't warm up at all! Oye! Going to go to another shop tomorrow and try a different brand just to see. But this is just one of those really wierd gremlins that we get occasionally...and it drives us nuts! Thanks again for all the advice so far...I'll let you know what shows up and what I find out.
01-07-2008 05:54 PM
Jmark Ahhh, another planehead! LOL Rebuilt a few P&W 980's and a Lycoming back in the day, but I digress.

You say that with the old radiator, it ran at 205 so you upgraded to a 3 row and it ran fine. While apart, you decided to change thermostats and installed a Mr. Gasket. Now you have a problem with running too cool. You again install another Mr. Gasket thermostat and nothing changes, still too cool at times. My thinking would be to install a totally different brand of thermostat and try again.
Over the years, i've run the cheapo Auto Zone and checker and they worked fine year after year. I"ve run the high dollar ones too and they ran fine year after year. My thinking, at this point, would be a bad batch of Mr. Gasket thermostats.

Even if you have a 40 row radiator, if the thermostat is working correctly, it will hold at the rated temp. Also, 15 minutes for warmup is not out of the ordinary. My 350 takes about that long to get up to temp. My other truck is up to temp in about 1 1/2 minutes!

Start with the easiest one first AND were things seem to have changed.....thermostat.

01-07-2008 05:34 PM
Thanks guys.

Okay, some really good advice here. So, to start diagnosis, or maybe even help come up with some goes.
It is a carb engine. That is the reason for the 180 therm. Plus, the engine is newly rebuilt, and a brand new engine tends to run warmer, so I wanted to make darn sure that the therm opens up soon enough.
I have burped and filled every possible air pocket in the system, so I am positive there is no air in the system, so that can't be it either. Flow of coolant is superb, no cavitating, and the hoses have a great "feel" to them while running. Now, I have made no changes at all yet...but I drove it last night, the thing came up to 180...after running for 15 minutes, and then today I drove it again, and it never made it above 110! It's killing me. Every logical troubleshoot I have is being laughed at me by this engine. Ive built many engines, and had great sucess. I've once or twice had to change cooling systems because they were getting too hot, but I have never had one unable to warm up! Shoot, I've got a half a dozen aircraft engines under my belt as well...and I'm the once who test flew them too...I have plenty of faith in my skills, but this one has got me totally stumped!
01-06-2008 08:59 PM
russlaferrera Put the thermostat in water with a thermometer and verify the opening temp.. You need to start someplace.

When the engine is at operating temp how is the coolant flow?
01-05-2008 08:26 PM
Engine running too cool...totally baffled!

You should be able to touch the valve cover at operating temperature but if you can keep your hand on it when it is at operating temperature a vapor lock could be the problem. It stands to reason that if you run a 190 thermostat for example, the motor will run at 190+/-. If you have not done so yet, try spending a bit more time burping the system to get rid of the air bubbles.
Hope it works for you.
Are you running a carb or EFI?
If it is a carb, I would go to a 190 thermostat. If the engine runs much higher you'll get performance troubles. Especially when you go to restart when it is still warm.
If it is an EFI, it's OK to run the higher temps.
Where is the temp sensor located? Is it on the side of the block or at the top. The side of the block will usually give you a higher reading than on the top.
By the way, a 383 is nice in that truck.
01-05-2008 03:44 PM
Originally Posted by Hotrodder78

Okay, I have searched the forums and found a couple of hints to my problem, and tried all the solutions, but for some reason, I still have no answer.
I have a SBC 383 stroker in a 84 pickup. New motor, just built it and it runs like a top! At first, I was running the old 2 row radiator on it with a brand new water pump. It ran a little warm...205 and that was in the winter, so it made me a little nervous about summer. (I live in Georgia.) So, I swapped a new 3 row radiator brand new, and that has not been a problem yet. Kept the engine nice and cool. Now, when I did this, I also decided that while the engine was drained, I'd go ahead and replace the thermostat. Put in a new Mr. Gasket 180 Therm. Sealed it up, and the engine never got above 110. After driving in town for 20 minutes, I can still put my hand on the heads, hoses...etc. I thought maybe I got a bad therm. just by chance, so I replaced it with another new one. Same problem. I check the works...check the sending, and have mad certain that there is no air in the system, no leaks, and that there is water moving to and from the overflow tank. Plus, if it were really getting to 180, I couldn't hold my hand on the Cylinder head! Oh, one more thing, Mechanical fan, shroud, and a good fan clutch, so that has been checked also. Does Mr. Gasket just make Sh***y thermostats, or what? That is the only thing I can possibly think it might be. Anyway...This thing should run great if it's at 180, but at 110, it runs like an engine that is not fully warmed up. Any suggestions would be great! Thanks.
Once in awhile you might get a bad thermostat - my guess is you have an air pocket in the cooling system.

I just went through this after replacing my heater core the engine wasn't getting to temp and the heater was blowing cold air.
01-05-2008 01:08 PM
carsavvycook If your air/fuel ratio is rich it will help keep your engine from heating up. Remember Lean builds Heat and Heat builds Horsepower. 200 to 215 is ok. Personally I like to run 210-212 using 195 degrees thermostats.
01-05-2008 07:20 AM
barnym17 210 to 215 is best for your engines health.Not always best power but best longevity.The reason for this is higher thermal efficiency, also the moisture created as a by product of combustion is steam at these temps and easily removed by the pcv system. Also oil should be ran at least at 220 degrees but less than 300 for best life and power due to friction and thermal losses at lower temps.The reason most engines have seemingly less power at higher temps such as these is because the under hood temp will normally match coolant temp give or take a few degrees and hotter under hood air is less dense cutting power somewhat. The rule seems to be for every 10 degree drop in air intake temp adds 1% in power.The best deal is 210 coolant, 240 oil, and as cold as possible intake temp.I.e scoop, cold air induction etc.
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