FasterIsBetter

I've dealt with overheating problems for many years with old Jaguars, particularly the XKEs. They were designed for British conditions, where a HOT day is 75*F. In the US, where we regularly get temps in the 80s and 90s, the systems just can't keep up with it.

In my experience, you must stick with Occam's razor when it comes to solving overheating. The situation described sounds like too little air moving through the radiator at idle, plain and simple. If it runs cool at highway speed, it should run cool at idle if enough air is going through the radiator and enough coolant is going through the engine.

When I was a kid, in the 50s and 60s, I remember my dad having to put the car in neutral when we were stuck in summer traffic coming back from the Jersey shore, and revving the engine a bit to get the coolant circulating and the fan moving air. People were always overheating. When I started driving, I did the same thing when stuck in traffic and the car would start to overheat. And it worked. Modern cars have solved the cooling problem, but old ones still do it.

So, solution? I would say that it's time to consider upgrading the fan and clutch to one of those 6 blade fans that move more air at idle. Alternatively, consider putting in a pusher fan in front of the radiator to move more air. And when sitting, don't let it idle low. Keep the idle up a bit, like 1500 to 1800 rpm so that the coolant is circulating through the radiator and the block. Remember, the longer the coolant is in the block, the hotter it is going to get, so you want to keep it moving.

One other suggestion -- get a bottle of Red Line Water Wetter and add it to your coolant. I've used it in old cars for a long time, and it definitely helps keep things cool. I've also used it in a couple of C5 Z06s that I owned and raced, and never had an overheating problem on the track or otherwise.

JohnZ

What do you have for a fan shroud, fan blade, and fan clutch?

Have you read this article on Corvette cooling systems?

KingD

Thanks for the article. I will definitely read it. The fan shroud, fan blade and fan clutch are either original or installed during the 1990 restoration with Long Island Corvette parts.

Thanks for the help.

I tried burping the air out of the block/system, so I am down to air flow across the radiator and timing. I did reset the timing after the rebuild and it is pretty close, but worth some additional tweaking.

Stan's Customs

What cam did you use?

tuxnharley

Is the fan clutch engaging when the engine is hot? You should be able to hear it make noise when it is engaged when the engine is hot.

From your description it seems you reused the fan clutch that was there before the rebuild. How was it stored while out of the car? IIRC if you store it improperly the fluid will drain internally past an orifice and the clutch will just spin freely and not move air.

I don't remember the details - maybe one of the other members can fill in the specifics.

A non engaging fan clutch would cause the symptoms you are experiencing, with over heating at low speeds while running cool at speed when there is airflow.

KingD

The cam is a speed-pro, but the machine shop installed it and I do not have the model, so not much help with this.

I don't recall how I stored the fan and clutch, so I will check this out. How do you test this to know whether or not it is functioning correctly?

The other thread also talked to timing, so I am going to seek some help from a professional and have them set the timing, so I know that it is set correctly.

I ran the engine with the expansion tank cap off and burped the air, but that did not seem to help.

The shroud and fan are original design and should be okay.

Thanks for all of the trouble shooting help. Without this forum, we would not be able to get this car to the point where it is today and a hope of getting it to where it needs to be. You are awesome and for this I thank you!

Stan's Customs

The cam question was directed at timing...that seems to be the major change in the swap that you have mentioned so far. The specs would help when setting the timing...


You stated that the fan and clutch are the same although the problem sounds like classic symptoms of air flow. (and yes the oil can leak out of the clutch as mentioned).

Powershift

You don't need to just "set" the timing, you need to "map out" the centrifugal and vacuum advance curves to see exactly what you have. The "cam" you installed will change your engine vacuum and may require a new vacuum advance unit. You also need to see how the centrifugal advance comes in with RPM and what your total mechanical advance is. Ideally, you probably want about 6-12 degrees initial advance and a total mechanical advance of abut 36-38 degrees all in by around 3000 RPM.............but this can vary with engine modifications (or lack thereof). The vacuum can should add another 12-16 degrees of vacuum advance at idle when you connect the hose to a full time vacuum source. Make certain the vacuum can will be "all in" at least 2 inch vacuum less than your normal engine idle vacuum reading. This keeps the vacuum can from surging the timing and creating an unstable idle.

The archives have a lot of info on this subject if you check.

When you changed engines, it changes other requirements as well.........so something that worked okay before may not be okay now.

Larry

Stan's Customs

..exactly. with a little less total advance on some engines.

Faslane

My dad told me years ago, if it runs hot going down the road it is the radiator, if it runs hot at a stoplight is circulation, if it runs hot with a/c on it is the clutch fan, worked for me 30+years.
I would not drill anything, I think the timing
would have to be way off?
Always fill a small block through the intake where the heater hose connects to.
always run a new motor fat, lean is mean!
shut it down at 240 and read the plugs.
After you get it figured out I would go back to the 180 therm.

Sky65

Yeah these these temps don't don't make sense to me either. I missed them in your 1st post. You may want to recheck them but take a look at this 1st. Especially point #3.
http://www.thermoworks.com/blog/2012...d-thermometry/

Your new cam and subsequent tune may need more initial timing and less mechanical. My suggestion is to record what you have now, as a base, before making any changes so you can put it back if necessary. Record initial timing with vac adv disconnected, total with mechanical, and amount of vac advance. Also note rpm of max advance initial and mechanical. Post results.

Tom

Faslane

No disrespect, NEVER do total with the vacuum advance hooked up.

If you can post a good pic of one of the plugs, I can tell you if your timing need less or more, can tell you your idle circuit is rich or lean, and running and WOT is rich or lean.
but I don't think that timing is your problem, those temp you got on the radiator seem sketchy. I would jet it up two or three numbers tho to be safe

Powershift

I don't think SKY65 meant that.......but his statement can be interpreted a couple of ways depending how you read it.

Larry

Faslane

Sorry, a lot of people miss that one, including me years ago,

Sky65

Agreed! I didn't make that very clear. Total being initial and mechanical, vac advance disconnected. Thanks for catching that.

Tom

KingD

I have a new fan clutch on order and an appointment with a turn C2 mechanic to help me dial in the timing. Thanks!