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  #11  
Old 07-15-2019, 06:28 PM
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Whitetrash Whitetrash is offline
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Originally Posted by Steeveedee View Post
I was tempted to just run without the shroud, but that's not an answer. It's been running up to 260F when pulling hills with the travel trailer. That's usually a clog in the coolant circulation. It also ran hot at idle, which is air flow. I put a new radiator in it but that didn't help. I went and bought a tester to see if there were combustion byproducts in the coolant, but that showed no combustion leaks- no burnt gaskets or cracks in the heads or block. But I did notice that the flow was pretty puny. So I pulled the thermostat and checked it on the stove. It opened when it should, so even open, there isn't enough flow. So, I drilled 3 holes in the thermostat flange. Now it sits idling in gear at 195F instead of creeping up to 260F. This is a 180 degree thermostat, so I'm thinking once I get the fan shroud coupled with the fan for air flow that that will bring it down more. Note that this all goes on without even using the air conditioning. The truck should run with the AC on and not overheat.
You might consider plumbing in a oil cooler to take some of the load off the cooling system.
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  #12  
Old 07-15-2019, 10:11 PM
Steeveedee Steeveedee is offline
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You might consider plumbing in a oil cooler to take some of the load off the cooling system.
It has a trans oil cooler, but it is in a position where it doesn't get a lot of air flow, up behind the bumper. I'm looking at a scoop that doesn't interfere with radiator flow. If you meant an engine oil cooler, I'm considering that, too. The engine seems to have survived the 260F excursions, but that is just too hot for my liking. I had a '66 Pontiac Le Mans with a Ram Air 3 400/400 trans that turned low 13s in the 1/4, and it ran hot as Hades in traffic (260F, again!). But it only had a 3 row radiator and a baloney slicer (flex) fan.

I put a severe duty fan clutch on the truck, but gained very little in the way of cooling. The biggest result so far was from drilling holes in the thermostat flange to increase flow. It makes me think that the water pump may be an issue, even though it isn't all that old. Of course, it has run hot for the whole time that my FiL owned it too, so even putting a new water pump (replaced a leaker) on it 9 years ago may not have been the total answer. I do know that whenever they (my parent's-in-law) pulled into a stop to get gas when camping (with or without a trailer), they had to wait for the truck to cool off before it would start. That was a symptom from '81 when I married my wife, and it had always been like that since they bought it in '73. I was a mechanic for many years, and this one is providing a challenge to my knowledge. But Ima fixit!
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  #13  
Old 07-16-2019, 03:05 AM
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MetalWolf MetalWolf is offline
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It's a '70 Chevy with a big block 400. I went to a 20" fan from 18" for the added cooling capacity. I measured the stock shroud, which is 21" inside the "tunnel", but I didn't catch that the fan wasn't centered in it and the new one rubs on the bottom. I can bend the sheet metal over a form, but I'd like for the strap to be nicely curved. I guess I could just hammer it into submission and paint it black to hide the hammer marks.

The old fan also was too far inside the shroud and didn't couple with it that well, so the new shroud will match the fan better. I looked online but there is nothing with a 21" opening for the fan. A factory shroud won't work, and even the formed ones only appear to have a 16" opening for the fan.
Did you mean small block 400??? has it ever had head work done ???
Anyway, I don't remember chevy making a BB400 in 70' so most likely an SB 400...

Easily mistaken for a 350 and if it's ever had head work two things could be going on either wrong heads been replaced one or both or wrong head gaskets 400 have larger water passages and a couple of extra cooling water passages...

This was a common problem/Mistake a lot of mechanics made in the early '80s... and more so in the '90s

I think in 1970 through 1974 is when the SB 400's came out, They Make one hell of a street rod engine and they are rare to find today...

the only way your going to be able to tell it from an SB 350, 307, 327, 283 is find the casting numbers on the back of the block look it up and the casting numbers on the heads and see if they match numbers for the SB 400 if the are numbered to anything but that there is your problem those engines were known for running cool even worn out ran cool around 140 in a high upper 180
we could not get mine to run hot in my SS El Camino and it was by far a stock engine at the time and bored 60 over...

Anyway, there is a way to fix that problem using a set of old school 194, or 202... 350 heads and 400 head gaskets...
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Last edited by MetalWolf; 07-16-2019 at 03:17 AM.
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  #14  
Old 07-16-2019, 09:06 AM
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Originally Posted by Steeveedee View Post
So, I drilled 3 holes in the thermostat flange. Now it sits idling in gear at 195F instead of creeping up to 260F. This is a 180 degree thermostat, so I'm thinking once I get the fan shroud coupled with the fan for air flow that that will bring it down more. Note that this all goes on without even using the air conditioning. The truck should run with the AC on and not overheat.
Just a thought....
Have you replaced a lower rad hose recently?

I have a JD 544B front end loader. I had to replace everything because the machine was burned when I bought it. The lower rad hose was burned but a bit of coil spring was visible. I went to the dealer and he told me the spring was nonsense and they could not order one.
After boiling the rad twice, I started to think. I stood beside it and had someone rev it up and the lower hose sucked flat.

I was scrapping some ford diesel trucks at the time and I found a spring in one of their lower hoses that was close enough to size, and put it in.

Problem solved.
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  #15  
Old 07-16-2019, 09:33 AM
Steeveedee Steeveedee is offline
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Metalwolf- It is a 402 BBC, people just call them 400s a lot. It even says 400 Cu In engine on the sticker in the glove box. It's definitely a big block, 7 bolts holding each valve cover on.

Ironman- All the hoses are new, but that's a good thing to check. I'll do that. It is running cooler since I drilled out the thermostat flange, so maybe not, but it's easy enough to do.

Now, I'm off to the hardware supply to get some thin plywood (or cardboard from their trash) to make up a template for the metal sheet for the larger part of the shroud.
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  #16  
Old 07-16-2019, 10:26 AM
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Originally Posted by Steeveedee View Post
Metalwolf- It is a 402 BBC, people just call them 400s a lot. It even says 400 Cu In engine on the sticker in the glove box. It's definitely a big block, 7 bolts holding each valve cover on.

Ironman- All the hoses are new, but that's a good thing to check. I'll do that. It is running cooler since I drilled out the thermostat flange, so maybe not, but it's easy enough to do.

Now, I'm off to the hardware supply to get some thin plywood (or cardboard from their trash) to make up a template for the metal sheet for the larger part of the shroud.
Ok Chevys oddball 396 block factory bored to a 402 CI... Now that makes sense.
A bit rarer than the SBC 400... never known them to be called just a 400 though... GM's 402 were commonly used in trans AM's
That engine requires a 4 core radiator...
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  #17  
Old 07-16-2019, 10:44 AM
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Originally Posted by Steeveedee View Post

Ironman- All the hoses are new, but that's a good thing to check. I'll do that. It is running cooler since I drilled out the thermostat flange, so maybe not, but it's easy enough to do.
Be sure to check it hot with the 'stat open.
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  #18  
Old 07-16-2019, 11:24 AM
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Originally Posted by Steeveedee View Post
The fan is too far into the shroud already, with the shortest fan clutch available. The engine was rebuilt many years ago and it was reinstalled in the forward position on the frame, based on the visual cues. So, I'm making a shallower shroud instead of making all the changes to put it back. I'd have to cut the exhaust and a bunch of stuff that I don't want to do.
Chevy made a "long" water pump and a "short" water pump for the SBC. I think the short was for earlier (60s) cars. And brackets were different between the two. I don't know if that is the case with BBC.

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Originally Posted by MetalWolf View Post
Did you mean small block 400???
He answered this below...

Quote:
Originally Posted by Ironman View Post
Just a thought....
Have you replaced a lower rad hose recently?
Good point--missing spring may allow hose to collapse...

Quote:
Originally Posted by Steeveedee View Post
Metalwolf- It is a 402 BBC, people just call them 400s a lot. It even says 400 Cu In engine on the sticker in the glove box. It's definitely a big block, 7 bolts holding each valve cover on.
Trucks usually got the big block 402 while full size cars (Caprice, Impala) got the small block 400. There is one sitting in the parking lot at my shop (not mine). I owned an Impala 400 for about a week. Bought entire car with an engine miss for $50. One pushrod and rocker arm later I had a sweet runner. Yanked engine and trans and sold for $500. Gave rest of car to my buddy who did a lot of "free" towing for me.

Quote:
Originally Posted by MetalWolf View Post
Ok Chevys oddball 396 block factory bored to a 402 CI... Now that makes sense.
A bit rarer than the SBC 400... never known them to be called just a 400 though... GM's 402 were commonly used in trans AM's
That engine requires a 4 core radiator...
I think the truck would say "400" on the fender somewhere when they came with the 402. The Oldsmobile 403 was used in Trans-Ams and would say "6.6 liter" on the hood scoop.

PS: and the 401 was used in AMCs...
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  #19  
Old 07-16-2019, 11:59 AM
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One more thing to consider and check. Are you sure the temp reading is correct? I have run across this issue troubleshooting a "hot" engine. Finally traced to a bad temp gauge reading.
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  #20  
Old 07-16-2019, 12:48 PM
threepiece threepiece is offline
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Is there anyone close to Simi Valley (back of beyond, yes I know) who has a roller and a brake? I need a piece of 1/8" aluminum strap rolled to a 21" diameter, and a piece of 25 gauge aluminum sheet formed on a 1/2" radius.
I'm surprised by the common belief that you need special machines to bend and otherwise process metal. The reality is for the most part, machines only make the job easier or faster, they do not make the job "possible". With some material you may already have on hand and a few tools you likely have both of these forming operations can be easily done on the bench.
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