Re: 71 350 running hot coolant backup up problem
Gun i used in my thermoformers took temps 1 inch apart accurately , but it was 600 bucks
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Re: 71 350 running hot coolant backup up problem
Don't give up on your temp gun yet! I use mine almost daily (I'm a mechanic) If you measure right at your thermostat you can actually "watch" the Tstat open & close (pretty cool) In so doing you can verify it is working & it's opening at the correct temp. Don't get too picky about exact numbers, if a 180° opens at 185° it doesn't matter, close enough.
to confirm your gauge is accurate you need to shoot the sender in the driver's head. From what you posted it's close enough. So, from what you've posted, your engine & your gauge are doing pretty much what you thought all along. This is good to know. My opinion (FWIW, everyone else has given theirs!) you've covered all the basics, some more than once. The one item you have not addressed is the radiator. You can look down the tank & it "looks" good but you cannot see down the tubes & these are what get clogged. Take your new gun & shoot the radiator starting at the driver's top (hot coolant in) then shoot various points to the pass side bottom ( cooled coolant out) In perfect world, you want to see about a 50° drop across the radiator. Time for a radiator (easy for me to spend your $ but it's still cheaper than an engine!) side note: 50/50 mix (or any ratio) versus straight water will not make any difference. From the tech articles I've read, water with a "wetting" solution removes heat the best BUT the difference IN A PROPERLY OPERATING SYSTEM is negligable. |
Re: 71 350 running hot coolant backup up problem
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Re: 71 350 running hot coolant backup up problem
Anti freeze isn't in the radiator for cooling. Its to keep the water from freezing in the winter time and to lube the water pump and keep the system clean that's all.:chevy:
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Re: 71 350 running hot coolant backup up problem
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so I may have discovered something that may save you some grief or at least save you some money if you ever experience something similar to this
but first let me tell you the last thing I did before this discovery I went out and dropped $200 on a brand new cheap Spectra "Premium" radiator, of the plastic and aluminum variety |
Re: 71 350 running hot coolant backup up problem
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here is a closer look at the Spectra Premium A369 radiator
it measures almost exactly the same, except the top parts that are supposed to fit into the rubber mounts on both the left and right sides are too wide so I had to cut and use 5" strips of an old mountain bike inner tube to use as buffers between the metal brackets and the aluminum radiator instead of the stock rubber pieces |
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mandatory stare and compare of the old brass/copper radiator and the new plastic and aluminum one
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Re: 71 350 running hot coolant backup up problem
So what are the findings?
So now with a brand new stock 195* thermostat, a brand new short water pump, a brand new plastic/aluminum radiator, running water only (for test purposes only)... The truck idles fine in P-Park I think it was like 135* F after 15 minutes of just sitting there, it would slowly warm up more, but I decided to take it for a spin It cruises at 185* F, however and here's what I recently discovered, when stopped at a stop sign or at a stop light, it will climb North of 200* F in just one minute, now this is in D as in Drive OK, yeah so what? Well I decided to shift it into N for Neutral and sat at an isolated Stop Sign for five minutes and the truck never inched past 195* F, now that has to tell us something! Right? I also tried it in reverse, I pulled into a parking lot and backed into a space and left the truck in R-Reverse and sure enough in just one minute it reached 200* F your thoughts? |
Re: 71 350 running hot coolant backup up problem
Sounds fine to me ,,, fer an ole truck ! :chevy:
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Re: 71 350 running hot coolant backup up problem
I still think you should put a 180* t-stat
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Re: 71 350 running hot coolant backup up problem
OK, let me do the TL;DR version-
You have a new water pump, new radiator and new thermostat. Is this true? If so, check for a blown head gasket/cracked head, etc. |
Re: 71 350 running hot coolant backup up problem
I see what your getting to I think. The transmission is causing the rise in temp when in gear. The temp will be added to the radiator as hot transmission fluid passes through it.
I run a external on all of my vehicles.:chevy: |
Re: 71 350 running hot coolant backup up problem
Looking at your pictures your bypassing the heater core which would add about a gallon in volume , i would use a 180 thermostat and for a few bucks more the Champion all aluminum radiator that many guys use and like that fits well . :chevy:
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Re: 71 350 running hot coolant backup up problem
Two things I can think of
1. How much is your rpm dropping when you go from p/n to d/r? If the engine slows, so does the water pump. Might kick up your idle and see if it changes the result. The trans front pump is pumping fluid thru the cooler no matter what gear you select, so that’s probably a non issue. 2. If you are running Vortec heads, they have a different cooling passage setup compared to non Vortec heads. I don’t remember exactly, but it has something to do with the water pump bypass and how that is routed thru the block. If those heads are used on an old style block you have to accommodate for that. Might be worth a bit of research to ensure you aren’t chasing that. |
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Re: 71 350 running hot coolant backup up problem
I’d set the idle to around 650 in drive and see what happens. What’s it idling at in gear now?
You may have to play with initial timing and idle screw adjustments (throttle plate and mixture) to get it so the neutral to drive rpm difference isn’t too extreme. Like add timing and lessen the throttle opening, or change up ported vs manifold vac to the can. The usual hide the salami carburetor adjustment game... |
Re: 71 350 running hot coolant backup up problem
This may sound kinda silly but try jacking up the front of the truck. Get it as high as you can while still being relatively safe. Take off your radiator cap and see if ya get any bubbles. You might have a big air pocket stuck in the back of the engine. Just an idea.
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Re: 71 350 running hot coolant backup up problem
Do a couple cartwheels and a backflip ,, that'll do it ...
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:lol: he's jumped through enough hoops already, this couldn't hurt. |
Re: 71 350 running hot coolant backup up problem
Just a thought.Do you have the wire like, a coil spring in your lower hose? I know it wouldnt matter at idle, but when driving the hose could suck shut restricting flow?
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Re: 71 350 running hot coolant backup up problem
No matter if you are running vortec heads or not a by-pass hose is a good idea. The factory put one it for a reason. The by-pass keeps the water circulating through the block and heads and eliminate hot spots.
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Re: 71 350 running hot coolant backup up problem
You can get a 3 core polished aluminum champion radiator on eBay now for $205 with free shipping
I just picked one up last month. Fit very good. Good deal https://m.ebay.com/itm/1967-68-69-70...gAAOxyBPZTid8U |
Re: 71 350 running hot coolant backup up problem
I did notice the 850 RPM idle speed you mentioned sounded about 200 RPMs high but since some people like what I would consider a high idle so I didn't want to judge.. I prefer a putta-put-put - maximum 650 RPM or as low as I can get it to run smoothly in that neighborhood. You definitely don't want your centrifugal advance coming in at whatever idle you wanna use.
Hey I may have been wrong about your initial timing being the cause of your overheating but just maybe I was on the right track with my second choice of the heat possibly coming from your TH350. If so it is too bad I wasn't smart enough to link your high idle with the trans fluid shearing forces maybe creating too much heat in the fluid. Maybe a sniff test of your fluid will help to tell the tale. Luckily you can drive it now just put it in neutral at the stoplights. |
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