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Old 06-21-2017, 04:28 AM   #26
Mike_The_Grad
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Re: Mishimoto Electric Fans in Your 67-72 C10?

Your idle mixture screw adjustments depend on what carburetor your running. I run my original 1972 quadrajet 4mv on my 350. I had my screws at about 3/4 turn out from seated. This was way off. I chased every possibility of why I was having hotter coolant and engine temps. Like I previously posted it was due to a few things happening at once.

First off I had a big vacuum leak at the rear of my factory cast iron intake manifold. I didn't put enough silicone down to seal the intake along the rear of the engine block. That was my fault for not taking into consideration of having my engine block decked by the machine shop.
I also had a leak at my carburetors base gasket. Relatively easy fixes.

Also like I mentioned previously, burping my coolant system properly made an obvious improvement.

I learned that most quadrajet carbs respond well to around 4-5 turns out. This may seem like a lot, but it doesn't hurt to try, you can always turn them back in. Mine are set now at about 4 3/4 turns out.

Once I addressed my vacuum leaks and tuned the carb through trial and error, it straightened my temperature fluctuations right out. The engine idled smoother, responded better, and I won't say it "had more power" but it was utilizing the power it already had more efficiently. It wasn't easy, especially without a shop or a mentor, but I figured it out. That's how I'm able to hopefully provide some insight into your issue.
I hope yours is a simpler and quicker issue to fix because summers just getting started, and Vegas isn't somewhere you want to have overheating issues anytime of year.
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Old 06-22-2017, 02:15 AM   #27
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Re: Mishimoto Electric Fans in Your 67-72 C10?

Thanks for the ongoing replies. Still no fix. Ugh! (It was 115 degrees out in Vegas today)

- Update: I checked total timing with vacuum line off and plugged from vacuum advance. Initial was 12 degrees (BTDC) and total was 36 degrees BTDC at 3,000 RPM. That sounds about right. I have a bit of a cam but not sure how much.
- All cooling system components are new.
- T stat is 180 degrees.
- Not bubbling over when engine is turned off.
- As I drive it eventually gets deep in the red on the gauge and 230 degrees on the lower rad hose (bottom of rad to pump) using IR gun regardless if open highway driving or in town driving. Top hose is 20 degrees cooler. Sounds backwards, doesn't it. Summit claims it's the right pump.
- It never pings
- Water pump replaced last summer (Summit high volume pump)
- Nothing blocking airflow. Installed Mishimoto's twin electric fans (2600 CFM total) and their 3-core aluminum rad, both designed specifically for 67-72 C10s. I also temp installed a pusher fan on front of A/C rad (1100 CFM), still over heats, but slower and only slightly into red area on gauge.

The only other strange thing is I've started getting what sounds like belt squealing occasionally when engine is cold. It's not a belt. Torque converter maybe?

Next step is to look hard for any vacuum leaks before installing a new water pump. Keep the ideas coming. They are Enormously helpful!
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Old 06-22-2017, 05:59 AM   #28
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Re: Mishimoto Electric Fans in Your 67-72 C10?

Wow. That last post provided a lot of good info.

Everything in your post seems spot on with what you'd consider ideal conditions for operation. I have only a few more theories as to what's going on. After that I'm stumped.

1. Are those mishimoto electric fans installed correctly? I don't mean it as an insult, but from what I read on the jegs site it doesn't say if they are pusher/puller fans. Where is your A/C condenser mounted? If it's mounted directly in front of your radiator and has a large surface area, it could be interfering with the radiators cooling efficiency.
Being in Vegas means your A/C is probably running as much as your engine is. Are your A/C components in good condition? (Compressor, Heater core, no refrigerant leaks?)

2. Your radiator hoses seemingly being opposite of what you'd expect and you stating that you are starting to hear what may be belt noises is a big red flag to what I suspect is the root of your problem. I hadn't brought it up because I forgot all about it happening to me.

Before I had to rebuild my engine I had just freshened it up after it had been sitting for almost 8 years of not running and with just tap water in the block. I re-gasketed the engine,new distributor, rebuilt carb,new chrome aluminum hiflow water pump,belts,hoses,etc. Everything short of head gaskets. I got 4,000 miles out of it when it blew a head gasket. (They were 20 years old after all. Lol.) Thought a new head gasket set and about a week of work I would be back on the road.WRONG. Long story short it needed a rebuild. Block checked out good. Bored .040 over, New set of reman 882 heads, comp cam XE250H kit and I was back on the road a year and a half later.

Immediately was having hi temp issues. With the hose temperatures being opposite of what you'd expect just like you stated. But was able to keep the needle right in the middle of the gauge, then after about 100 miles started hearing belt noises, replaced belts, another 100 miles, belts again. This time i spun the water pump pulley and fan without the belt on it and i could hear the pump groaning. I wasnt thrilled at the thought of replacing my chrome aluminum water pump after only 5,000 miles or so. So I slapped on a stock cast iron pump. $30 & lifetime warranty, sure why not?

Just like that, my engine temperature woes were gone! Haven't had a single instance where the needle rises above 1/4 on the gauge. No heater core for assist. Stock fan, no clutch. Idling in traffic and 90 outside not a problem.

That damn chrome aluminum pump was a REVERSE ROTATION WATER PUMP. There was no identifying marks on the box or the body of the pump, I had to pull the impeller cover off and check the impeller blades to confirm it.
Yes, reverse rotation pumps are designed for serpentine belt driven setups. But they have the same flange and bolt spacing as standard rotation v-belt driven pumps.

And just because summit says it's the right pump, doesn't make it so. I would make certain it is the correct one.

Also, bad motor mounts will shorten a water pumps lifespan due to vibration and unbalanced rotation.
So even if it is the correct pump, it could be bad already. A pump doesn't have to be leaking out of its weep hole to indicate it's bad. In fact, most pumps have two weep holes. I dont remember why, but you can have a very slight amount leaking from one of them and it'll get blown away by the fan, or evaporate off the block before you can find it. That was the case with my chrome pump. I guess 5,000 miles rotating in the wrong direction will eventually cause something to fail. LOL.

That's all I have to offer for possible causes. I apologize for the long posts, but as someone who has experienced these things personally, and only about 2 years ago, I'd like to know I wasn't the only one to have it happen to.
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Old 06-22-2017, 08:41 AM   #29
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Re: Mishimoto Electric Fans in Your 67-72 C10?

Reverse Rotation Water Pump.

These are made I think for the serpentine belt systems where the belt wraps around the water pump pulley in reverse ( spins the pump backwards ).

Anybody know of a way to determine which direction the pump is pumping?

-klb
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Old 06-22-2017, 09:56 AM   #30
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Re: Mishimoto Electric Fans in Your 67-72 C10?

have you pulled any spark plugs to see if it is lean ? it sounds like a coolant flow or air flow problem not fuel or timing . what lb radiator cap are you using ? does it puke coolant into overflow tank? you might pull the stat and test it. keep us posted
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Old 06-22-2017, 10:11 AM   #31
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Re: Mishimoto Electric Fans in Your 67-72 C10?

Mike,

That's an awesome/terrible story but sure sounds similar to mine. I really appreciate the post.
- To give you an idea on space, there is 2" between A/C condenser and radiator, also 2" between radiator and water pump pulley mount bolts
- I put on new motor mounts about six months ago, a few months after I put on the new water pump.
- I haven't pulled the rad cap and done a pressure check, great idea
- I haven't pulled plugs in a while either, another good idea
- It's not filling up the overflow tank. Just the opposite, it's using coolant but not a serious amount yet

Tomorrow I think I'm ready to start with the water pump change. I'm putting on FlowKoolers 1671 https://www.summitracing.com/parts/BRA-1671
It might take some time to report back to y'all cause I'm going to also remove headers and clean/paint the engine bottom since I'll have everything removed. It's the matching ser# engine with the truck ('70 C10), I'd like to keep it!
Once again, can't say thanks enough for all the ideas.
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Old 06-24-2017, 04:19 PM   #32
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Re: Mishimoto Electric Fans in Your 67-72 C10?

I pulled the pump off and the back plate.

So, here's the million dollar question.

From the view of the camera (engine side), which direction do you all think the impellers should turn to draw coolant FROM the large inlet? CW or CCW?
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Old 06-24-2017, 06:01 PM   #33
Mike_The_Grad
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Re: Mishimoto Electric Fans in Your 67-72 C10?

It appears that you have the correct pump for your application. The coolant actually gets "flung" off the "backside" of the impeller blades. So yours looks to be correct.

Did you notice any signs of coolant leaks under the pumps shaft on the out side of the engine block? It would show up as dried white spots on aluminum parts and isn't easily wiped off. If you don't have any coolant leaks, then you may have air trapped in your cooling system.
A trick I learned is to drill a 3/32" hole in the thermostat. It allows the air to be purged out while filling up the system.

Also check the pump for any sounds while you spin it by hand. Spin it both directions. It should spin smoothly and freely in both directions. Check the end play of the shaft by pulling/pushing In on the shaft with your hand, there shouldn't be any noticeable movement back and forth.

Which coolant are you running? I know that you can't run the old green type coolant with an aluminum radiator or cylinder heads. You need dex-cool or some other aftermarket coolant because of the dissimilar metals.

If you already have the new pump, slap it on there and run it. Burp your system real good. You can leave you rad cap off and warm up your engine to help any air bubbles escape. Is your radiator cap the correct type to allow use of a reservoir? Some don't, they just "pop" to relieve pressure.
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Old 06-25-2017, 03:46 PM   #34
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Re: Mishimoto Electric Fans in Your 67-72 C10?

Ha! I stumbled across this pic I took a while back of a page from "Classic Industries" catalogue for 1947-present Chevy and GMC trucks. I completely forgot that I had taken this pic, but I remember the reason I took it was because it was the most definitive way for checking my water pump at the time. Hope it helps you in some way.
( sorry it came out sideways.)
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Old 08-12-2017, 06:48 PM   #35
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Re: Mishimoto Electric Fans in Your 67-72 C10?

I put on a FlowKooler pump that draws into the inlet regardless of rotation direction just to be safe. Adjusted my idle way down so 1200 in park and 550 in gear at a stop. Still too much drop but I don't get into temp needle red, just short of it.

No vacuum leak at all, mixture screws 1 1/2 turns.

Mishimoto, Edelbrock, Summit, and two local motor shops have all reached the same conclusion at this point: I need more airflow. The Mishimoto 2600 total CFM on these two fans is just not enough for me, probably cause of the cam.

I have 2 Derale 2100 each CFM fans (4200 total) coming along with their PWM adjustable fan controller. I'll let you know if that fixes my overheating.

Anybody interested in the Mishimoto fans? : >)
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Old 08-13-2017, 10:30 AM   #36
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Re: Mishimoto Electric Fans in Your 67-72 C10?

Just my .02 cents, the new fans will fix your overheating problem. A BB engine needs at least 3000 if not 3200cfm to not overheat. I went through everything you're going through with mine about 5 years ago, learned the hard way that Griffin radiators are epoxied not welded so they break down and leak. Their fan kit is top notch and I don't run hot with it installed on my stock 4 row radiator. Troubleshooting overheating problems ranks right up there with colonoscopies and can be just as expensive!
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Old 08-13-2017, 11:16 PM   #37
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Re: Mishimoto Electric Fans in Your 67-72 C10?

Ok, I just got to say that the last post from engineer_gregh was priceless. Lol!!
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Old 08-13-2017, 11:21 PM   #38
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Re: Mishimoto Electric Fans in Your 67-72 C10?

Glad you still have your sense of humor:-) Sometimes these trucks can be frustrating.
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Old 08-14-2017, 11:14 AM   #39
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Re: Mishimoto Electric Fans in Your 67-72 C10?

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Old 08-17-2017, 01:31 AM   #40
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Re: Mishimoto Electric Fans in Your 67-72 C10?

So here is the conclusion to this thread story. Thread summary - I changed every component in the cooling system. Tried 3-core alum rad, hoses, two temp sensors, 2 gauges, 2 water pumps, 2 thermostats. Checked timing, carb mix screws, etc etc. A really annoying overheating problem all year here in Las Vegas.

Mishimoto's twin fans (2600 CFM total) couldn't keep my '70 C10 402 from overheating at slow speeds/idle.
https://www.mishimoto.com/chevrolet-...oud-67-72.html
Their fan controller did work well though.
https://www.mishimoto.com/adjustable...oller-kit.html

So, those of you who said I just needed more airflow were dead ... right!!
I just put in two Derale 14" fans (2100 CFM each, 4200 total) and wow, those little hurricanes have no problem keeping the engine cool. Finally!!
I also installed Derale's PWM fan controller which automatically adjusts fan speed to match temp I set and also has a soft start ability. And yes, they run after ignition off but only for 1-2 mins at very low RPM, no problem to the battery.

So worth the $150 more for the Derales fans and controller than what I paid to Mishimoto. Perhaps other Chevy big blocks cool down well with the Mishimoto fans, but mine sure didn't. I guess I now know why there are no Mishimoto reviews on Summit or Amazon for the fans I got . They don't do the job.

So I tip my favorite hat to all you who helped me on this post, great team effort (and sense of humor). I'm a happy C10 man.

http://derale.com/products/electric-...fitting-detail

http://derale.com/products/electric-...n-probe-detail
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Old 08-17-2017, 06:00 AM   #41
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Thumbs up Re: Mishimoto Electric Fans in Your 67-72 C10?

Nice setup and now you can enjoy the ride! Which it's all about in the end.
Another small detail that will help is make sure you seal off the fan shourds around the edges to force the air through and not around the radiator.
Really any place air can go around the whole system needs to be blocked off if possible.
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Old 08-17-2017, 10:38 AM   #42
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Re: Mishimoto Electric Fans in Your 67-72 C10?

Glad to hear it is fixed . Thanks for the follow up solution. nice fans by the way!
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Old 08-19-2017, 12:51 PM   #43
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Re: Mishimoto Electric Fans in Your 67-72 C10?

I'm happy you got it worked out. Nice setup by the way. I just picked up a derale 18" heavy duty stainless steel flex fan + 2" fan spacer for the sbc350 in my '72 c10. I'm sold on Derale.
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