Engine running hot after timing change

[Black70c10]

So, my sbc was set at like 19 degrees BTDC because I had experimented and at one time decided that it ran best right there and had the least amount of bogging. My accelerator pump is fine (rebuilt carb) and so whenever I felt like I had bogging at WOT, I would adjust the secondaries and usually this helped..I run supreme gas and with the mechanical radiator fan, this truck cruises all day at 190 degrees and maybe slowly approaches 200 if its sitting for a while...

For some reason, the thing started to bog at WOT all of a sudden and adjusting the secondaries did little to nothing so I thought I'd mess with the timing again. So, I dropped it from 19 to 15 and seemed to have no effect. I then dropped from 15 to 12 and bam, under WOT it had very little bog. Only now, as I'm sitting at the red light, it's climbing to 220 and looks to be leveling out at 225! When I start cruising it again it only drops down to like 215...

I think I understand why it's hotter-more compression as its igniting closer to TDC thus more heat? Not sure how I can get this thing to avoid bogging at say 15-17 degrees BTDC so I can run it cooler. Help is appreciated

[68gmsee]

What engine are you using that requires premium gasoline. Only thing higher octane does is reduce the combustibility of the gasoline so in essence it becomes less explosive. Unless you have a high compression engine, I'd stick with regular.

Also, what carb are you using. There's a lot of internal carb problems that can cause it to bog and lots of information on the web about ways to resolve.

Lastly, overheating is the same. Can be caused by several things. Some are listed below.

-Timing advanced too much. (Check initial and total, vacuum advance and mechanical for proper operation.)
-Radiator cap and/or thermostat.
-Lower radiator hose collapsing when going at higher speeds. Old ones had a coiled wire inside. New ones don't but they're stiffer.
-Fan clutch to make sure it's not leaking if you have a silicon filled clutch.
-Rodding out the radiator.
-Installing an overflow container with proper radiator cap to go with it.
-Leaking head gasket or even cracked head.

[i82much]

Overheating can be caused by too little timing. If your engine likes 12 degrees initial, you need to figure out how to get more timing in it at cruise. You can do that by adjusting the mechanical curve or the vacuum curve. If it runs well at full throttle now without any detonation anywhere in the RPM range, I'd suggest adding some vacuum advance if possible (e.g., adjustable vacuum advance).

[brown7373]

As 68gmsee said, how about some more information. What year and engine, carb, compression, cam etc. And are you running vacuum advance, and what about your mechanical advance. Is it working and what is it set at?

[Black70c10]

Thanks for the input everyone. I'm running supreme because the engine has a bad tendency of dieseling if I run lower octane. Unfortunately the previous owner did not even know what cam specs or compression. I'm running an edelbrock performer 650 and have an MSD dizzy with no vacuum advance.

Sounds like I may need to investigate getting more advance for total timing because setting the base around 12 seems to give no bog at WOT.

[68gmsee]

Seems like you probably need to really go down to the basics on this one and tackle one problem at a time.

The dieseling can be caused by the timing too far advanced, the overheating problem or carbon build up.

Vacuum advance is used when engine is at lower RPMs and is basically not used at WOT. This is where the mechanical advance comes in. Vehicles used for racing generally run at WOT so no need for vacuum advance but in normal day to day, you should have one.

Then make sure your timing mark is correct by insuring it's at exact (TDC or "0") when #1 piston is at top dead center on compression stroke and time the engine to specs depending on what the distributor manufacturer recommends for your engine. 12-16 degrees should be okay for HEI type.

Once you're sure the timing is correct check for overheating as mentioned above and continue with trouble shooting.

[Black70c10]

Thanks, I'll see what I can do... When I first bought the truck, I did confirm the balancer's timing marks are correct. Previous owner said he always ran premium because the vehicle was used for eighth mile racing and as a high compression ratio.. Of course I didn't think to ask at the time what the ratio was and now can no longer get a hold of the guy..

Anyway, timing is set around 15 now and it runs good and cool just a little bog at WOT.. Still working the issue...

[imjeff]

Higher octane fuel allows you to run more timing without pinging it. Sounds like a sudden change so maybe a bad tank of fuel?

[68gmsee]

Originally Posted by imjeff

Higher octane fuel allows you to run more timing without pinging it. Sounds like a sudden change so maybe a bad tank of fuel?

Agree. Higher octane lowers the combustibility of gasoline so it would in essence allow or require more advance in the timing. If the engine is high compression that may be the reason it runs better on the higher octane and requires more advance.

The overheating may not be related to the timing. Trouble shoot the it first since that's the important one at this time.

[imjeff]

Not trying to start a debate here, but, this change was "sudden". Probably not timing, unless the clamp bolt was loose. Probably not jets because it ran fine...jets don't suddenly change. Accelerator pump only affects the transition from cruise to WOT, not WOT. Sooooo, sudden change in operating temp with no change in timing or carb adjustments must be something that changed suddenly.....bad fuel, clogged fuel filter, bad ignition module, clogged radiator, change in ambient temperature, etc.

High compression, regardless of whether it happens through piston design, blower or turbo results in more power. To maximize power we use higher octane fuel (more power, better burn) to run max advance. Your motor ran fine with its mechanical advance and without vacuum advance. None of those have changed so they aren't the problem. Anything that has not changed since it ran good cannot cause your problem. Good diagnostics involves looking for horses when you hear hoof beats, not zebras. Keep it simple, your motor didn't gain compression spontaneously.

[msgdsrf]

Your engine bogs at WOT from too much "total" timing and overheats from too little timing at idle. If you were to keep the initial at the 15 and hook up the right vacuum advance canister (2" below idle in drive) to full manifold you'll get the idle advance that will keep your engine at a good temp. My best guess is to try a Standard VC-204 (Delco D1334C) can hooked to manifold and your good to go.

You likely did get bad gas, it happens alot. When you're on the edge with your previous tune, it just shows it more.

[WIDESIDE72]

Since the teuck was running good then suddenly developed the overheating issue, i feel the same as those above that mentioned a bad tank of gas or that regular got switched for suler somehow. If it were my truck i would install a dist with vacuum advance. This would allow better acceleration at low rpm without having to advance the mechanical advance, therefore avoiding detonation at higher rpm. As mentioned above vacuum advance is really a neccesity on street driven vehicles.