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#1 |
Registered User
Join Date: Nov 2014
Location: Austin
Posts: 749
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Fan shroud diagnosis/help
1971, 350cid, automatic with a/c. Generally, engine temps are fine except during periods of idling in traffic with a/c on and air temp 90 degree plus. Temps come down immediately upon moving. no boil over, but temp guage climbs to read zone, radiator outlet temp too high (200+). The fan shroud is the obvious issue (gap), I need a new shroud due to the current one being cracked broken in many places. But, the fitment of the shroud is the issue.
I assume shroud should be tight to radiator so air doesn't get sucked into the gap (low pressure zone) instead of being pulled through the radiator. Help on what parts I need to order would be appreciated. I assume I would start with a a/c shroud from LMC (currently on sale for $50). Here are some photos: First is top right, showing gap. Radiator side tank fills bracket channel. ![]() Second is top left. Radiator side tank does not fill bracket (shorter than right side), brackets are both same (right and left side). ![]() Finally, bottom gap. Clips hold bottom off radiator with equal gap of 3/4" or so consistently around shroud. ![]() |
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#2 |
Registered User
Join Date: Jun 2014
Location: lakefield,mn
Posts: 566
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Re: Fan shroud diagnosis/help
I think that you have the wrong upper radiator mounts or wrong radiator. Looks like you have the 4 core mounts on the smaller radiator. I believe the front edge of the shroud should sit almost on top of the rad.
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68 c10 swb stepper 68 c10 swb stepper 67 c10 lwb 06 gmc duramax |
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#3 |
Registered User
Join Date: Nov 2014
Location: Austin
Posts: 749
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Re: Fan shroud diagnosis/help
Definitely possible it is the wrong radiator. The right tank flange is wider than the left tank. right flange fills the bracket channel, left does not. It is not a 4 row radiator.
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#4 |
Registered User
Join Date: Feb 2011
Location: Modesto, CA
Posts: 2,188
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Re: Fan shroud diagnosis/help
While your radiator may not be stock, that gap is pretty normal (maybe a touch too big) for a stock shroud and radiator setup (also for an aluminum rad like Champion). It can be reduced using some clever ingenuity however. You are correct in thinking that is a culprit of reduced airflow, but it shouldn't be the reason why your truck is slightly overheating.
Some things to check and consider: What condition is your water pump in? What condition is your radiator in? What condition is your temp sender and gauge in? Have you verified the high temps with a temp gun? Is your coolant fresh and debris/rust free? Do you have a proper clutch fan, with operating clutch? Have you added any fix-it-all bottles like water wetter? Is your system maintaining adequate pressure? A quick fix to see if somehow that gap is causing your overheating issues, is to cut a piece of cardboard or plastic and fill the gap. If it works then you can go about constructing something that works and looks better, but again, I don't think that minimal gap is causing your issue. Last edited by leftybass209; 11-23-2015 at 03:29 PM. |
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#5 |
Registered User
Join Date: Aug 2006
Location: Redmond, WA
Posts: 6,332
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Re: Fan shroud diagnosis/help
Rubber weatherstripping to fill the top gap and black duct tape to seal the bottom/sides as needed. Or just tape the whole thing up temporary and see if it makes a substantive difference at all.
Honestly it looks like you have the wrong top mounts, as others have likely said. I'd get the rad to match rather than downsizing the mounts, if possible.
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1970 GMC Sierra Grande Custom Camper - Built, not Bought 1969 Pontiac 2+2 427/390 4-speed Coupe 1969 Pontiac 2+2 427/390 4-speed Convertible |
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#6 | |
Registered User
![]() Join Date: May 2013
Location: WEST PALM FLORIDA
Posts: 1,174
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Re: Fan shroud diagnosis/help
Quote:
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68 Long Fleet , ly6 , turbo 350 , 3-5 drop , original paint , front discs 67 Small window , 7 foot bed , tweaked 6.0 LSX 2004R Medium Olive 58 Apache fleet , 235 , offy intake , dual exhaust , 4 on the floor , red/white 69 Long Fleet , Custom , 6.0, 4l60 , AC , Medium Olive |
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#7 |
20' Daredevil (Ret)
![]() Join Date: May 2003
Location: Jefferson State
Posts: 13,646
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Re: Fan shroud diagnosis/help
All good advice above. My gut feeling is a weak or failing fan clutch (assuming the fan itself is an adequate design).
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- Mike - 1972 K20 LWB 350/350/205 RIP El Jay |
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#8 |
Registered User
Join Date: Nov 2014
Location: Austin
Posts: 749
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Re: Fan shroud diagnosis/help
Thanks for responses. In no particular order:
No fan clutch New water pump New temp sender (proper sender with proper range). Mounted in intake (won't fit in heads). Normal running temp is lower quarter of normal range. Radiator cleaned and pressure checked pofessionally. Fresh 50/50 coolant/distiller water No stop leak or similiar used. No evidence of same. Radiator maintains pressure and does not loose coolant. Never over heated, just veyr close. Seems I have seen shrouds very close/tight to radiator. Also, I don't trust radiator cleaning effectiveness. I suspect radiator, works perfectly other than idling in traffic on hot days. Probably marginal flow through rad or even block. |
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#9 |
Registered User
![]() Join Date: May 2013
Location: WEST PALM FLORIDA
Posts: 1,174
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Re: Fan shroud diagnosis/help
A sugestion , try some "blue ice" additive to your radiator , its cheap , Ive had good results with it in the past
__________________
68 Long Fleet , ly6 , turbo 350 , 3-5 drop , original paint , front discs 67 Small window , 7 foot bed , tweaked 6.0 LSX 2004R Medium Olive 58 Apache fleet , 235 , offy intake , dual exhaust , 4 on the floor , red/white 69 Long Fleet , Custom , 6.0, 4l60 , AC , Medium Olive |
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#10 |
20' Daredevil (Ret)
![]() Join Date: May 2003
Location: Jefferson State
Posts: 13,646
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Re: Fan shroud diagnosis/help
It would probably be more ideal if the shroud sat closer to the radiator, but I doubt that's much of a problem. Since it gets hotter than you'd like while idling in traffic, and does not have a clutch fan, I would install one. It makes a world of difference. The fan blade design is so much more aggressive than a typical fixed-blade fan, to move a greater volume of air when needed.
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- Mike - 1972 K20 LWB 350/350/205 RIP El Jay |
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#11 |
Old member
Join Date: Jan 2002
Location: Liberty, & Garden City S.C. , U.S.
Posts: 19,936
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I close up all the gaps in mine with black foam. This forces the air through the radiator. I have AC also which it helped with that also. Make the air go through it not around it.
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1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 ![]() Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs. |
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#12 | |
Registered User
Join Date: May 2008
Location: S.W. Chicago, IL.
Posts: 317
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Re: Fan shroud diagnosis/help
Quote:
If you're using the factory in dash temp gauge with a sending unit in the intake, I wouldn't trust the reading. A stock sender for stock gauge should be in the head. If your sender only fits the intake and not the head, it's not for the factory in dash gauge. It may read close, but don't trust the accuracy. There are many threads about sending units and factory gauges on this board. It's very difficult to find replacement senders that work accurately with a factory gauge. |
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#13 | |
Registered User
Join Date: Nov 2014
Location: Austin
Posts: 749
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Re: Fan shroud diagnosis/help
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#14 | |
Registered User
Join Date: May 2008
Location: S.W. Chicago, IL.
Posts: 317
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Re: Fan shroud diagnosis/help
Quote:
Radiator cleaned & checked + new water pump, and it's not boiling over, is a good thing. Maybe the sender in the intake is giving an inflated reading on the high end. You could do what I did on my '72 350, add a mechanical temperature gauge. I got one of those aftermarket fancy chrome triple gauges. The temp gauge has a flexible hard line with a "bulb" on the end that threads into your head, or intake, with various thread adapters included. Mine is in the DS head and gives me a very accurate reading. You don't have to do a triple gauge, you could just add a single temp gauge somewhere under dash. Run that bulb sender to the small port in your head. You can run both temp gauges and compare. |
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#15 | |
Registered User
![]() Join Date: May 2013
Location: WEST PALM FLORIDA
Posts: 1,174
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Re: Fan shroud diagnosis/help
Quote:
__________________
68 Long Fleet , ly6 , turbo 350 , 3-5 drop , original paint , front discs 67 Small window , 7 foot bed , tweaked 6.0 LSX 2004R Medium Olive 58 Apache fleet , 235 , offy intake , dual exhaust , 4 on the floor , red/white 69 Long Fleet , Custom , 6.0, 4l60 , AC , Medium Olive |
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#16 |
Registered User
Join Date: Nov 2014
Location: Austin
Posts: 749
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Re: Fan shroud diagnosis/help
No, not Vortec heads
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