FJ 40 SB Chevy conversion running hot? (1 Viewer)

[pb4ugo]

On my 72, I've been running a sbc stk crate for 20+, ramshorns, single exhaust, qjet. A very aggressive 5 blade 35* 18" steel straight fan and made a fan shroud with the fan properly oriented in the shroud. 160 t/stat, it runs about 180, and might go up to near 200, wheeling in KY on real long climbs. Overheating isn't a problem. Timings set at 10*.
For the last year & half I've been driving my 75 40 on the street. It's runs a 350/nv4500. 3.70 gears and 33" tires. It runs about 1700 rpms at 60mph according to an rpm calculator. I dont run a tach. I recurved the dist with lighter advance springs so mechanical total advance of 34* is all in around 2000rpms to tune for fuel mileage. I use the stk Toyota temp gauge in the cluster. The needle registers just past the second line. According to Toyota the 3rd line is 210* I don't remember what the tstat is. It runs a cheesy plastic flex fan in the stk 40's fan shroud. The po's mechanic installed the driveline and moved the rad to the right to center the fan in the shroud. It doesn't overheat either.

 

[B y r o n]

What brand/model electronic fan are you using? Some electronic fans are more efficient than others.

 

[79FJ40TLC]

On my first FJ40 with a SBC/350 I ran a GM 7-blade fan with heavy pitch and a severe-duty thermal fan clutch from a 1-Ton ( mid-eighties application ) 454 for a 4.56 gear option - stayed engaged longer at higher RPM’s.
That motor used a 180* thermostat and even in the Florida heat it never broke 195* under all day hard use off road - even running the sand dunes.
The radiator was a replacement core OEM unit - nothing special and no shroud.
Mechanical fans draw an enormous amount of air when a proper fan clutch is used. This combo was an option on a lot of Cab Chassis applications from GM in the 70’s, 80’s and very early 90’s.

My current FJ40 will have a GM 292 in it and I plan on using the same cooling setup as it was bullet proof in my old L/C and every old school GM truck I have owned - a really well proven and tested setup.

Tom

 

[texcwa]

Mine runs mid 180's to mid 190's, occasionally may get to 102 - 105 (on hot uphill drives). Made my own fiberglass fan shroud and just using standard flex fan. This is before I painted it.

 

[JohnnyFish]

Mine runs mid 180's to mid 190's, occasionally may get to 102 - 105 (on hot uphill drives). Made my own fiberglass fan shroud and just using standard flex fan. This is before I painted it.

View attachment 3358003

I'm using the same fan. What did you use to shape your shroud? Looks very pro.

 

[texcwa]

I did it about 15 years ago, from what I remember, I cut a rectangular piece of 1/4" plywood (same dimensions as face of radiator) held it in place to inside face of radiator, cut a round piece of 1/4" plywood (I believe I cut it 1" larger in dia than fan blade so to have 1/2" clearance from edges of blade) and attached (taped) to front of fan blades, cut a length of 2 x 4 to fit between center of ply on radiator and center of round fan piece of ply, traced with marker the two ends of 2 x 4 so to get both angle (motor sits with a 5 deg slope back) and distance.

I then removed the plywood pieces, cut another 2 x 4 an inch or so longer (so that the round piece of ply would line up to center width of fan blades, screwed together to make a skeleton, wrapped an XXL T-Shirt around face of round fan ply and pulled very tight to around back of radiator ply and stappled it. I the applied a couple thin coats of resin to the T-Shirt to make it stiff, then started to apply several strips of fiberglass and resin to make it solid. I then cut away the plywood (leaving just the edge that the fiberglass shroud was glued to), Sanded and painted.

After cured, cut in half so to install, riveted some small aluminum angles an both halves to attach together (made for simple installation), and made a couple of top straps and a bottom strap that were again riveted to fiberglass shroud.

Hope this makes sence.

 

[troutbum4]

Stock mechanical fuel pump on mine. It’s reliable and stops running when the engine does if I crash. : /

a 3 year battle for engine temps, would routinely run about 220, I think (knocking on wood) I've gotten it fixed. Last year was a new radiator w shroud, high flow water pump and larger fan. Better, 210 ish. This year new thermostat that was more compatible w the high flow water pump, 25/75 water to coolant and a bottle of water wetter. Looks to be running about 190-195 now. Will see how she likes Montana this summer. Running an electric fuel pump, added a relay that shuts it off after 3 seconds if the engine is not running....... my intent was so I could run the electric fan while at the gas station to avoid heat sink, but should work also should I crash......

 

[JohnnyFish]

If you added front disc and kept the '72 master and didn't pull the front residual valve that is why the disc stayed against the rotor. Drum residual valve is 10 psi and disc only needs 2 psi or none at all.

Residual valve deleted. Huge difference. No disc drag in my five mile round trip for coffee today. I think my overheating issues are solved. Thanks again!

 

[peesalot]

Did those big fittings come right off, I have tried 3 times over 20 years and never had any luck getting those to move at all.

 

[JohnnyFish]

Did those big fittings come right off, I have tried 3 times over 20 years and never had any luck getting those to move at all.

Yep, though I had to use an impact on the bigger one. I soaked some PB Blaster on it first for a little while.

Some of this build is pretty fresh. The odometer on the custom gauge cluster indicated just 500 miles when I bought the truck a couple years ago.

 

[texcwa]

Those with SB Chevy conversion, what’s your temps running at?

I have SB conversion with Vintage Air AC system and two speed electric fan. My temp is reaching 215 degrees. Is this normal, all good or start over?????

Thank you all,

Ben

View attachment 3356969

As I have mentioned in a previous post, I did not have room for a fan clutch. I ended up using a 17" flex fan with homemade shroud. Since many have commented on the use of flex fans and what damage they can cause, I just switched to a solid 17" mechanical fan. Before switching, I wanted to somehow check the air flow through the radiator with the flex then compared to the new mechanical fan so I did the following. Note this is not really scientific but gave me a base line to work with.

I first placed a wind speed (mph) hand held monitor near the center of the radiator, see photo below. I then took readings at various RPMs at the same location each time. I did this with the shroud on and with the shroud removed. You will see in the chart below that the shroud made a greater than 20% difference in the amount of air pulled through the radiator.

I then ran the same serries of air flow tests with the new fixed mechanical fan. The results (difference) did Suprise me that the flex fan at lower RPMs pulled more air but at higher RPMs the mechanical pulled more (this would be expected from the Flex in the flex fan.

The one difference is that the shroud was made for the flex fan having 50% of blade inboard the shroud. When I installed the mechanical fan I had to change the fan spacer from 1 1/2" to 1/2" (due to fan offset design. This put the mechanical fan having approximately 2/3 of the blade inside the shroud, 1/3 out v 50/50. Below again shows the method and results. Both fans had a clearance of approximately 1 1/8" from face of radiator.

 

[sogncab]

Hope this makes sence.

Dude. WFD

 

[peesalot]

FWIW my 1970 dual circuit drum MC runs my 4 wheel disc no issues, no proportioning valve. I used 3/4 tom GM bolt on calipers in front and gm metric calipers out back. Either my residual valves no longer function or I am lucky.
Every time I have had a caliper get sticky its cause I pressure washed vehicle and blasted the brakes, learned my lesson and never wash brakes again. I use dry silicone garage door lube to coat everything for rust prevention( cause dust/dirt dont stick to it) , leaf springs, calipers, door hinges, hood hinges, etc.

 

[texcwa]

Dude. WFD

Sorry for the ignorance but I’m 63 yrs old and am not on social media (except forums like this). what does WFD mean?

 

[sogncab]

Sorry for the ignorance but I’m 63 yrs old and am not on social media (except forums like this). what does WFD mean?

Well F-ing Done

 

[texcwa]

Well F-ing Done

Thanks, sogncap, it's the sh--s getting old, lol

 

[sogncab]

Thanks, sogncap, it's the sh--s getting old, lol

No worries!

Gives me some ideas, and I have to imagine those smooth curves flow far more efficiently than flat panels bent at angles to make a shroud.

@fjdiesel will need a new shroud soon for his rig. I want to try making a plug out of foam on the cnc, glass it, then chemical melt the foam out.