Running hot, need bigger fan and other tricks advice please

[patrickt]

Originally Posted by CHANMADD

If the Fan switch is too low, it will run all the time.

This is the fan thermo switch ERA uses. It's a 75 Centigrade switch:

Switch, fan thermo -- 1980-1984 VW Rabbit, Jetta: 823 959 481/75

Why would VW even make a fan switch that ran the fan all the time? If you wanted it to run all the time you wouldn't need a switch. If your lower radiator hose can't get below 167 degrees Fahrenheit then something is not right.

[twobjshelbys]

I always drilled a small hole through the thermostat near the top as well. Supposedly helps bleed air

[bcrumpley]

A couple thoughts on this. Being that you are in Houston, I’d run 75% water/ 25% coolant along with Water Wetter. I would install a 180 degree thermostat and set my fan to come on around 185. Start cooling it before it’s up to 210 plus.

You say your engine is a 520 cubic inch FE. I don’t know what the bore is, but those cylinder walls must be pretty thin. Nothing you can do to change that, but these changes along with a fan that moves more air and optimal engine tuning might get you where you want to be.

[767Jockey]

Originally Posted by bcrumpley

You say your engine is a 520 cubic inch FE. I don’t know what the bore is, but those cylinder walls must be pretty thin. Nothing you can do to change that, but these changes along with a fan that moves more air and optimal engine tuning might get you where you want to be.

It's a BBM block, the walls are still plenty thick. There's enough meat left for a couple of addition overbores if needed. Thankfully that's not an issue in this problem. I get back home soon and I have a thermostat and a bottle of Water Wetter waiting at home for me to install when I get there. I'll see what if any improvement that makes and go from there.

[Dominik]

Originally Posted by eschaider

An unsolicited perspective;

If the engine is overheating at idle it is talking to you. It could be lean, it could be a timing issue, it could be an air leak somewhere in the intake tract. Properly timed, with adequate fuel, an engine should not overheat at idle.

Same findings here: At idle you mobilise 20 hp and the equivalent in heat to get rid of.
I kept my car in South Africa comfortably under boiling three red traffic light sequencees in a row. At over 100°F. And stop go traffic.

One 16" pusher fan.

I feel that pusher and puller fans combined can cause air stall between them, resulting in lack of airflow.

What gets often overlooked is timing at idle, as mentioned above. A radical cam needs plenty of 16 deg. If you set a cam with loads of overlap to 6 degrees, the mixture will burn out the exhaust port causing your header to glow.

If your car overheats at speed (above 30 mph) then your radiator flows not enough air. But since you shrouded yours (completely?) this is not an issue. However, I advise to keep the gap above the radiator open to have some air flowing through the engine bay. Keeps the footwells cool.

For racing force all the air you can through the radiator. And suffer.

Put your thermostat in. Or a washer with a ⅝" hole. The seems to harmonize pressure all over the coolant system.

[767Jockey]

Since you were all kind enough to chime in with your opinions on my running hot situation, I wanted to provide an update so someone searching the forum due to facing a similar issue in the future might get some info on their problem as well.

I removed the surge tank (again, it's a FE) and lo and behold, there WAS a thermostat in there. It's my first time in there, and the engine builder had said he hadn't put one in, so beats me how it got in there, but there it was. It was a standard thermostat, 180 degrees, with the usual 1/8" hole drilled into the top center of the thermostat mounting flange. I removed it anyway, and replaced it with a new 180 degree balanced thermostat, supposedly "high flow". No idea what that means with comparison to a regular thermostat, but that's whats in there now. I drilled two smaller holes into the top of the mounting flange instead of one big one. I forget the size bit I used, but the total area is slightly more than 1/8". I put the coolant mix back into the radiator, and added a bottle of Water Wetter as well. This next point I believe may be the key to the new success. In looking carefully at the fan and shroud, in an area that is hard to see, there was a gap around one side of the fan where it meets the shroud. It was about 1/4" to 3/8" wide and about 5" long. There were a couple of much smaller gaps where the shroud meets the radiator. I sealed all those gaps up.

I just took the car for a 30 minute ride around town. Stop and go, traffic lights, etc. It never got over 85 degrees C, which is about 185 degrees F. Couldn't be happier with that. My only reservation with declaring victory over this problem was that the day when it was running very hot, it was about 90 degrees outside. On this run it was about 72 outside. I'm not sure we will have another day at 90 or better, and if we do I might not be home to give it the hot day test before winter (such as it is in Houston) sets in. Given all that, I think I'm in much better shape now than what I was before I did all this. Next year will be the test when it gets hot outside again, but I'm hopefully optimistic that I may have a handle on this now.

Thanks to all of you for the suggestions. Now that I can actually drive it, I have more of the typical new build bugs to sort out. They'll be in separate posts here on the forum seeking your opinon on the best solution. Thanks again!

[auratkachakkar]

I used to spend a lot of time on circle tracks in SC , NC and GA . We didn`t run a thermostat , but we did run restrictors/orifices in place of the tstat . With nothing in there , the coolant circulates too fast to get good heat transfer from the engine to the coolant ..... you have to slow it down . The only way to do that was to play with various sized holes until you found what worked . mobdro 2022

[strictlypersonl]

Originally Posted by auratkachakkar

I used to spend a lot of time on circle tracks in SC , NC and GA . We didn`t run a thermostat , but we did run restrictors/orifices in place of the tstat . With nothing in there , the coolant circulates too fast to get good heat transfer from the engine to the coolant ..... you have to slow it down . The only way to do that was to play with various sized holes until you found what worked .

I'm going to quote MadBill because he is a good explainer and I am too lazy to type basically the same thought.

"I think the concept arises from the fact that sometimes removing the thermostat worsens an overheating problem. Since with less flow restriction the coolant circulates faster, 'obviously' the overheating must be because it is moving 'too fast' through the radiator. The actuality is that the flow resistance provided by the thermostat (which of course is at the outlet of the system) greatly increases the pressure in the block and raises the boiling point so that local hot spots don't flash to steam and insulate the metal from the coolant. Such a process can snowball until a major meltdown occurs.

There is no support in physics for the 'too fast through the rad' theory, but excessive flow rate can create local cavitation in nooks and crannies of the block which would worsen the situation."

[strictlypersonl]

Duplicate post...

[Luce]

I want to dogpile on the no thermostat means the water goes too fast and doesn't have time to cool misinfo.

Yes, if ti passes through the radiator quicker, it has less time to dump heat. But at the same time, it doesn't stay in the block to gain as much heat either. The faster it circulates, the more BTU's the coolant can POTENTIALLY carry away.

Here's a tasty little trick to add to your idle cooling issue.
https://www.ebay.com/itm/12377961269...3ABFBMlKbqpolh

When I was a kid and got my first car, I studied everything in the service manual, including the hydraulic circuits in the automatic transmission and emissions BS. This little valve is to keep hot idle temps down. When the coolant temp passes 200 degrees, it switches the car's vacuum advance from ported to manifold. This bumps idle timing up from the typical 10-12 degrees to more like 18 where the engine will idle faster and much cooler. In the auto dark ages (mid 70s to 90s) they ran idle advance way later than an engine really likes to keep the catalytic converter hot enough to work.

Someone maybe 10 years back wrote a big dissertation on timing, and it's worth digging up and reading.

As for me, I have a 427W with megasquirt, and the 16" spal fan and a $100 fleabay universal radiator, and the only time I had a minor heat issue was wen the fan relay melted down. Megaquirt's timing map has no load idle around 16 degrees, dropping back to 13 at the top of the map.

[jknich]

I run manifold vacuum on all distributor cars. Limit vacuum advance can to 10-12. Runs cooler at idle. This thread on the Sunbeam Forum has a good article and info on manifold vacuum.

https://forum.sunbeamalpine.org/inde...-vacuum.29800/

[spdbrake]

https://www.stewartcomponents.com/in...ormation_id=14