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Is 220degress too hot?



Well, the 69 that I am working on is improving. It is now down to 220 degress, setting at idle. The engine is bored ,I think to 60 over(I forgot what the engine guy said, I'm gettin' old) and has 10.5 to 1 comp. The car (per customer) ran at about 180. This is a little surprising, since it calls for a 195 degree thermostat and is a Big Block. What's your opinion and what else can I do to get it lower. This reading is with a mechanical guage not the dash guage......Hmmmmm, maybe I ought to hook the dash guage back up, it may read 180, we know how acurate they are:)..........Steve

Most likely the thermostat is already ruined from the overheat condition, doesn't take much or long to toast one.
220 at idle seems like way too much. Step one would be to change it. If the engine still runs hot I would consider Step two, install a high flow water pump. The best buy appears to be Summit Racing. Step three, if all else fails and the engine overheats at highway speed would be to upgrade the radiator. Remember that by boring the cylinders the heat transfer to the water is increased thereby requiring more cooling capacity. Hope this helps....

Now Dale, you know that's not what I wanted to hear. You were suposed to say " Oh, that sounds good, for a Big Block". I think you are right though. Now all I gotta do is tell the Customer that he will need to spend some more money. What do you think about a cooler thermostat, say a 180 degree? I personnally feel like that once the thermostat is open, it's open. This is the second "new water pump I have put on it and the 2nd thermostat. It was running around 250 within a matter of minutes before so I definatly helped it. Also, I wonder, what the temp difference is between the thermostat housing and the head, where the sending unit is???????Steve

Steve,, You may be able to salvage the situation with an elecric fan to help when it is stopped. How is it on the road? My BB '67 ran hot at stop lights and in traffic and it wasn't bored .060 over. There has to be a lot of heat transfer with that engine. I wouldn't be suprised to find a big discrepency between the dash guage and a good mechanical unit. Try placing a couple of floor fans so they blow into the grilles to see if air flow makes a difference before you spend any more money. Sounds goofy but it works when you are running in a new cam or tuning, ect.
Tom, I thought about the fan idea today I just didn't have one handy(they have all been put up, it's winter here in Missouri). :) The roads are just terible here so I didn't want to get it out, I may try tomorrow though....Thanks......Steve
to hot

my 79 L82 was doing same thing this past summer I flushed the radiator with prestone heavy duty radiator flush and replaced thermostat with 180 threw the 195 in the trash GERALD
to hot

SSVETTE I agree with DDL-81 about the radiator. Get a 4 core radiator.I mostley deal with later ones does yours have a fan clutch?
As you know the gauges on a 69 (or any year) are not accurate to say the least. What I would do before you panic your client, is to hook up an external gauge to make sure the is actually running that hot. An example of this was cured at our shop last week. A client brought in his 72 LT-1
stating that the car was overheating, the gauge was reading 250 or so.. We installed a autometer external gauge and found that the car was actually running at 185. We then replaced the temp sensor and now everything is fine, and we were hero's in the customer's eyes. Just a thought....

Guldstrand Motorsports
Thanks for the help

Dave and everybody else, Thanks for your replies, and yes Dave you are correct, it was the sending unit. The problem I had believing that it was the sending unit is I had tried 3 units, the last being from Chevrolet, all looked identical. We had a 72 in the shop that we were mesureing vavle clearance on and I thought I would try his unit. Which BTW had a spade rather then a button. Well to make a long story short, that was the problem, the car idled and ran at about 190. Apparantly, even Chevy's books were wrong. I had ran into this problem before in a 75, but I didn't think the problem was the same because it had aluminum heads with a small hole unit, and we had trouble finding a sending unit that worked. This car is at home now in Memphis so this little problem is gone....Thanks again for all your help........Steve
Glad to hear you found the solution. Using a thermometer to test actual temperature is critical to ensuring that you will not dump a bunch of money on a problem that doesn't really exist.

I did have a big heat problem with my all stock '66 big block - it would run at 210+ driving easy around town and on the freeway I could keep it at 210 only by driving 55, but trying to sustain 70mph caused the temp gauge to creep up to the wrong side of the gauge... I used a thermometer to find out how hot I was really running - my gauge was indicating 210 when the thermometer said 205. It was comforting to know that I had been running a little cooler than I thought. What eventually cured my problem was ensuring that my cooling system was as efficient as possible.

I went through a check list to ensure that; I had a clean radiator, lower hose with spring to ensure it wasn't collapsing, the proper thermostat, that the clutch fan was working and that the shrouds and foam pieces (designed to direct air through the radiator - not around it) were in place.

After each step, I ran the car in traffic and out on the freeway. Flushing the radiator and installing a new 180 thermostat (instead of the 195 called for) lowered my around town temperatures some but didn't do much for freeway driving. My clutch fan was good - I tried a flex fan for a while and noticed no improvment. By reinstalling the foam pieces that channel the air through the radiator I picked up a few degrees on the freeway, but after pulling off the freeway and slowing back down (no more air flow) the gauge would start climbing again.

The last and most effective thing I did was to remove the water passage plugs from the side of the block... When I removed the first one, not a drop of water trickled out - when I stuck a wire in through the crud buildup I was rewarded with a gush of coolant and 30 some years of accumulated crap. I forced water in everywhere I could, water pump, thermostat housing and water passage plug holes to wash out as much of the crud as possible. I then buttoned it back up and flushed the system again just to make sure. I added distilled water and Redline's "water wetter" without antifreeze. The temperature outside was hovering about 100 that day - not uncommon for where I live in California in the summer. The car warmed up to 180 and then stayed there driving in traffic around town. On the freeway, at a sustained speed of seventy mph the gauge rose to peak of about 190. When I pulled off the freeway the gauge dropped back down to 180 pretty quick - and stayed there.

So as it turns out, the passages in the block had simply been clogged and cheapest fix proved to be the most effective. I have since put the 195 degree thermostat back in - runs right at 195 now - imagine that.

J Lance,

What a great response! Couple of places I'd have never thought to check.


.... Nut
J Lance

It has been so long since I have had a freeze plug out that I had forgotten what a mess can hide inside the block. We have no way of knowing how good of care previous owners gave their cooling system. Thanks for the refresher course.


[Edited by 59Tom on 02-16-2001 at 12:40 PM]

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