59BlueSilver

Okay, just got back. Ambient went up to 82 deg. Traveling at 40 to 50 mph, temp on gauge stayed at approx. 200 deg (just to the left of the mark before 220). Pulled in the garage, it soon dropped to 180.

Should I be concerned?

devildog

Check your timing, with more advance it will run cooler. Also have more torque and throttle response.

With vacuum advance unhooked and plugged, the advance should be 34-38° at 2500-3000 rpm. This will probably give you 16-18 ° at idle.

Joe

59BlueSilver

The tune up book says 4 deg. TDC, are you saying 16 deg. TDC? I would think you would burn holes in pistons with that...

59BlueSilver

It's running warmer going down the highway, does fine at idle. Sounds like the electric fan is fighting airflow. I do have clearance to install a fan but without shroud. Do you think that at highway speeds, it will cool better with the electric fan off, then manually engage it at idle?

JohnZ

Electric fans always create an airflow restriction at highway speed - they're made for idle/low-speed traffic cooling. I'm confused - where is your stock fan, clutch, and shroud? Got a photo of your setup?

59BlueSilver

The electric fan includes the shroud developed by DeWitts, so I removed the existing fan & shroud intending to run just electric. Upon further reflection, however, with a little trimming it may be possible to install the old shroud, not sure. Also in order to get 50-50 fan into shroud, it will put the engine fan very close to the electric, probably too close.

0Tom@Dewitt

I have always recommended shooting the IR gun at the thermostat housing and/or the metal inlet to the radiator. This might sound like the wrong place but here is my explaination for this method.

The surface area around the sender is not what the probe is seeing, especially if the sender is mounted inside the head. The heat from the exhaust manifolds are too close to the switch to get an accurate reading.

What I want to know from the gauge in my dash is what is the average temperature of the coolant coming out of the engine and going into the radaitor. Shooting the thermostat outlet tells me that. I don't like the reading from the hose because rubber is a pretty good insulator.

If you are getting that big of a difference in readings (thermostat IR gun vs gauge) , then I would say the gauge reading is wrong. This might be the gauge but I would consider a new sender. Not just any sender will work either. If you have a replacement unit I would dig out that old original and check that one. You could also get a aftermarket mechanic (dial) gauge to compare.

I would NOT use both fan systems. Either go electric or go mechanical but not both. I have had engine fans suck the blades of the electric fans back and distroy the electric fan blades.

I also understand that you are using a prototype "add on" fan kit that John put together for you. Since you are the first one to use this, check to make sure you have about 1/4 to 3/8" gap between the radiator and the shroud.

I very rarely dis-agree with John Z (damm purist) but properly designed fan systems do not create a restriction on air flow. Our shrouds incorporate relief flaps that will blow open if any back pressure exists. In addition, the hole created for a 16" fan will handle double the flow the fan is designed for before the flaps even move. This means you could have 4000 cfm flow through the radiator with zero back pressure, and that's without the flaps opening. Go higher, and the flaps open up.

59BlueSilver

I agree with everything you said, Tom, you know better. The gauges were just restored so I assume checked for accuracy. Sending unit is another matter that I have suspected for a long time. I have never tried another & you know of a good supplier, I'll get one.
But one thing bothers me, the 185 sensor belonging to the fan comes on at 185 (or close), according to the gauge. At which time, the housing reading is 156.6. This is independent of the gauge sending unit. Am I wrong, I've thought about this so much I'm getting confused!

0Tom@Dewitt

If the fans come on and you're only reading 156 on the stat housing I think I'd get a new IR gun or at least put new batteries in it.

59BlueSilver

Just checked my IR, it's within 1 deg. or less. We're coming into warmer weather now and I'm going to start charting my runs, recording temps in various locations (ambient temp, sending unit base, gauge reading, and thermostat housing) and see if we can make some sense of all this. I want to go back & put a 160 in instead of the 180 (I know, I know), but I want to chart the 180 first. In the meantime, I think I'll order a new sending unit.

Westlotorn

A previous post mentioned your timing and the only answer I saw was that your initial timing is set at 4 degree's.
If your centrifugal advance is not working you may be creating your heat with bad timing.
As was mentioned, rev the engine to 2500 -3500 and see where your timing is at speed.
Very important to know that number. At the 2500-3500 RPM you should see 34 to 37 degree's of advance. If you are sitting at 4 degree's with no advance at RPM the engine can heat up rapidly even with a good cooling system at speed. Back at idle the timing is correct and the heat will go back to normal. You should rule this out as one of the basic tests before spending more time looking for answers.
You are correct that over advanced timing can burn pistons, that timing would be at RPM and if you had 42 degree's at 3500 rpm rather than 35 degree's at 3500 rpm I would be very concerned. At idle degree's will not hurt a thing. Modern computer controlled cars run 16 -19 at idle every day. Total timing is the important engine control for power and safety of your engine internals. These engines should achieve total timing between 2,500 and 3,500, it will vary. See what yours offers.
Yours may very well be perfect as it sit and that would be great but you need to know what you have to cure issues. LARS has a great read on timing these Vette engines if you end up wanting advice on this.

rich5962

I'd stay with the 180*. As John said before, a 160* will NOT do anything to help your situation.

Excellent advice and diagnosis.

59bluesilver......You need a dial-back timing light. Do what westlorn suggests, verify the timing before you go further. Test your vacuum advance with a Mityvac and vacuum gauge. Use the Lars/Duke 2" rule.....at idle it should be all in 2" below manifold reading, then centrifugal all in for a total advance at speed. I think westlorn nailed it. It's a timing issue.

Rich

59BlueSilver

I agree this needs to be looked into and eliminated. I've always set my timing at idle, never at 3000rpm. Not sure i can stand being next to an engine running at that speed! Can this check be done with an ordinary timing light? I don't understand this method, there are no marks that high on the degree plate?

Last time I set it, 4 deg. was sluggish, so I set it at 6 or 8, don't remember. Also, about the vacuum advance. I bought one a few months ago from O'Reillys, a B29. I read in another thread that this wasn't correct, is it?
BTW, my engine is a '69 350 255hp with Pertronic III.

59BlueSilver

Sorry, missed your post, I was typing while you were entering i guess. Anyway, about this light, looks like they are a little pricy, can they be rented? Also, my vacuum advance is connected to my Quadrajet. Is that correct? I guess when I check with a vacuum gauge, it will tell me that. Anyone have a link to the Lars write-up?

rich5962

A dial-back timing light allows you to read higher rpm timing by dialing back the light an offset amount to see your total timing at the timing mark, where you normally read static timing. A regular timing light cannot do that because your balancer mark is too far away from the timing mark tab.

You only need to get it to higher rpm for a few seconds to get the reading. Don't worry about that.

I don't have the spec for a B29, but you can't just get one based on a particular engine. It's based on cam, carburetor, atmospheric pressure, etc and since your engine is a built 350 you need to find what it's doing at idle. You need to get a reading with a vacuum gauge at idle. Let's say it's 15". Based on the 2" rule, you then want a vac can that will be fully engaged at 13", at a particular advance spec. I'd speculate you probably need a B20/B26(Napa VC1765), which starts to move at 5"-7", then is all in at 11"-13" with a 8* advance.

Enclosed is a doc which shows the specs. Measure your manifold vacuum reading and this will help you select the proper advance can.

Rich

edit....we're writing together.....the Lars/Duke doc is enclosed. I don't know if you can rent a dial-back but it may be worth ownership for future adventures.


I'm headed out for the day on a Corvette inspection and won't be back till much later. Good luck. Others will chime in when they wake.

Frankie the Fink

You should do what Westlotorn suggests and check timing...my '63 250hp is speced at 4* but I run it at 12* BTW - the engine loves the extra advance. You will need the dial back timing light and yes it does get "hairy" standing bent over an engine revving at 2500+ RPM. It does only take a few seconds though and I try to never stand in line with the spinning fan blades and do NOT have any flapping clothing, shirt sleeves, gold bracelets or timing light wires near any moving (or hot) parts. You'll be fine.

59BlueSilver

Okay, Frankie, I've started looking for one and I do have a vacuum gauge. But if it's safe enough to run at 12*, why don't I just set it there and see if it helps the overheating issue?

rich5962

Yes you could try that, but it would be also be wise to verify you have the correct advance properly matched to your engine. Even if the timing change fixed your overheating at speed, it may cause other issues at idle.

You may not be advanced correctly at idle, and if so, that B29 on there now is doing nothing. You need a baseline, and that starts with your vacuum advance.

Pilot Dan

You mention "BTW, my engine is a '69 350 255hp with Pertronic III". That's not a 283 which really means, heat, fuel, and probably timing are all different from original car specs. That being said, check Voltage at the battery while running the engine above 1500 RPM and see if it is stable at around 14V. A bad Voltage regulator (overcharge) will play tricks on the Temp gauge and cause it to read high in conflict with the IR gun: Pilot Dan

59BlueSilver

I also converted to an alternator in support of the high performance fan, but will check the voltage as well to be sure.