rear gear change advice

[JOZW30]

OK, so I had my rear differential rebuilt a couple of years ago and I put 3.73 gears in it (it's what the car was born with and I wanted to go back to original), and I really have regretted it as the car now runs hot (doesn't boil over, but consistently runs about 200 degrees). It never ran hot like this before the gear change.

I've played with the timing (even had Eric redo my distributor and carb since the rear change), new radiator, water pump, thermostat, fan clutch is working properly, etc..

I really can't take the car on the freeway any more. Just basically a bad decision I guess.

My question is, I think I've got above average mechanical skills, if I read up, get the right tools, and follow the manual, can I change the gears out myself? everything else should be new. Hate to yank the whole rear and take it to a shop.

Thinking about 3.23's or 3.42's.

Used to be able to hop in the car and just enjoy it, now I look at the temp gauge every two seconds..........

Thanks!

Joe

[PxTx]

I feel if you want to do the job, than you can. Just have to have the right tools and a positive attitude. There is enough technical help on the net. Do you have any of the shims which were removed with the gears you took out?

I don't think your overheating issue is due to the gears. I've posted numberous times that I run 4.88 gears without issue. It is actually more of a street car than a race car. I get 12 mpg on average wiht a 327 and 2 Holley 600's, but have run at 5k R's on the highway for almost an hour straight and no issue.

[Nova Jed]

Just curious, water pump pulley the right dia to crank pulley dia? Water pump going south?

[Alss]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: pxtx</div><div class="ubbcode-body">

I don't think your overheating issue is due to the gears. I've posted numberous times that I run 4.88 gears without issue. It is actually more of a street car than a race car. I get 12 mpg on average wiht a 327 and 2 Holley 600's, but have run at 5k R's on the highway for almost an hour straight and no issue. </div></div>

I agree..something in the cooling system aint right..wrong pulleys..rotted impeller in the water pump..bad T stat..I would start there.

[JOZW30]

New (last spring) aluminum &quot;performance&quot; water pump.

New modified t-stat (tested before install).

Had 4-core radiator recored and tested.

Lower hose not collapsing.

Same (correct #s) pulleys as on car before rear change.

Moving the initial timing up or down hasn't really made much difference to the thermals. It can sit there at idle after start up and not go above 160-170 degrees all day. Start moving and it slowly creeps up and up and up and will stabilize pretty much just north of 200. Obviously hotter on hotter days.

I thought maybe we didn't get the block cavities cleaned out real good and it's clogged up? has anyone ever tried to pull the lower block plugs while the motor is still in the car? Guessing it's a bloody mess.

One last question about the fan clutch, when the motor is hot, and I shut the car down, should the clutch be tight, or should it spin by hand pretty easily?

Thanks again for responding the 800th &quot;my enigne's running hot post&quot;! <<GRAEMLIN_URL>>/smile.gif

[RPOLS3]

What about the sender or the guage? NJSteve documented issues with temperature senders with his T/A.

I agree with everyone else that the gear should not be an issue. I run a 3:73 in my Big Block/Auto/A-C Chevelle and last July (80's and humid day) it made the 200 mile round trip to SCR15 with the A/C on full tilt and ran 185-190 degrees on the road and ran up to 200 occasionally at a stop light.

[Plowman]

You don't say what your coolant mix is at,antifreeze protection. I found that any richer than -34 deg is to thick. This will cause the car to run hot down the road and not hot at idle. I would replace the fan clutch too.

[Salvatore]

I agree with everyone else...its NOT the gears.

[olredalert]

----Messy or not I would pull all the lower plugs I could get to. You may have only marginal flow thru the block.......Bill S

[ssl78]

when its at 200 did you ever take a infra red gun and take a reading going into the radiator and out of the radiator to see the temp drop

[Tommy]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ssl78</div><div class="ubbcode-body">when its at 200 did you ever take a infra red gun and take a reading going into the radiator and out of the radiator to see the temp drop </div></div>

I was going to ask the same thing. Those little heat guns are cheap and work great. I think they are still around 20 bucks at Harbor Freight. I check my header tubes, radiator, t-stat housing on my stuff with them. I agree with the Masses, it shouldn't be the gears. I ran 3:73's up and down the interstate for hours at a time without issue. I also don't think 200-205 is hot either... If your fan is flattening out at the higher RPM is won't push as much air as did before. I have experienced that with flex fans and tall gears. They would run cool around town but flatten out while flying up the interstate and my temps were higher then. Still, 200 isn't bad in my opinion. I do have large box fans in the garage that I run in front of the car with the hood open after hard drives. That's only because I don't like to watch the temps skyrocket after shutting off these old engines. I worry about cooking the bearings sometimes Hope I helped some.


Tommy <<GRAEMLIN_URL>>/3gears.gif

[JOZW30]

I have messed around with the IR gun. I was using it to look for any crazy hot spots but everything seems pretty symmetrical heat wise. If I remember correctly the temps were lower on the lower hose by about 10-15 degrees.

I just pulled the car out of the car jacket Sunday so I still need to tune and change fluids, so no big deal to drain radiator and try to pull some of the block plugs to see what kind of mess I end up with. I keep thinking it's a flow problem.

Anyone ever done this before?

Plowman, I need to pick up a coolant gauge but I shoot for 50/50. I didn't know too much antifreeze would cause a car to run hotter. Can adjust that when I refill from trying the block plugs. I only drive the car in Ohio summer (hopefully soon AZ, so I better get his fixed!), so what is a good mix/ratio to shoot for? If I pick up a coolant gauge what temp is best?

I do like the 3.73's............

Appreciate the input.

[JOZW30]

Thanks Tommy,

I have stock pulley's and fan with clutch.

Joe

[69SSZL1]

200 degrees is not bad. Try Redline Water Wetter in your radiator. It WILL lower your running temp. Make sure your radiator is not partially clogged with rust or debris. You may not be able to remove your block plugs, they are usualy stuck from age. Good luck!

[PxTx]

I would have expected more than 15 degrees difference between the upper hose and lower hose. I would focus on why that is and hold off on looking at the block. I think you are on to it with the clutch fan being loose after a shut down heat soak.

Friends in California run straight water for better heat transfer. You should run something like the water wetter or other conditioner to help the bearings in the water pump and keep the rust down. Antifreeze is just for that. You could run water in the summer and drain half of it and add Antifreeze in the fall.

There is also a great debate on the benefits of Evans Coolant, but I don't want to muddy the waters in this thread.

[JOZW30]

I'll try to the water with the water wetter (think you need the anti--corrosion stuff at least). and I think I'm gonna just get a new fan clutch and see what that does. Easy to do and not that expensive maybe I got a bad one last time.

[69SSZL1]

I use the Water Wetter added to 50/50 antifreeze/ water

[Kurt S]

All kinds of lubricants and anti-corrosion additives in coolants. I wouldn't run water. Coolant isn't the problem.
I'd make sure the water pump is good. 'Performance' in the description of a w/p isn't something I look for - often that means they've messed with the vane design.
Take a look at John's article - http://www.camaros.org/pdf/corv_cooling2.pdf

[budnate]

I had one kinda like this once finally figured out the custom stainless blades had lost there oomph at speed they went flat and was not moving air...your conditions sound just like mine did then, zero in on your fan and the clutch, you might install a new solid fan for a test.

[kwhizz]

Hummm!!!.......I would take that &quot;Performance&quot; Aluminum pump off and put a stock GM pump back on and see what happens........Performance = Chinese........

[JOZW30]

OK, well I only changed the water pump because the car was running too hot. It didn't get any hotter because I used this water pump......

Can't remember but I'm pretty sure it wasn't made in China (pretty sure I would have sent that back). <<GRAEMLIN_URL>>/smile.gif

It looked like a good quality piece.

I picked up a new clutch and also bought a spacer kit that will allow me to solid mount the fan to test before I install the new clutch. Hopefully I'll get to it tomorrow.

I'm gonna try to remove one of the block plugs just for kicks too.

The fan is stock and I put a new clutch on it at the time I restored the car (5 years ago). We'll know soon enough.

Thanks,

Joe