Thermostat and Pump bypass questions.. technical
 

Here's my problem..

I'm getting high temp spikes shortly before my thermostat opens. It'll, for a very short time, go to 225/250 before the thermostat opens and then it'll drop back to 180 or below. My temp gauge is accurate. When the temps spike you can hear one or two cracks and pops of steam hammer in the motor before the stat opens up. Once she opens in warm weather it tends to be OK with no more temp swings. If it's cooler outside the temp spike scenario can play out 4 or 5 times once the t-sat cycles shut. I have plenty of cooling capacity in the system, at idle or speed, so that's not an issue.

Here's what I have ..

It's an aluminum block Pond KC built 482. I'm running the Mr. Gasket/Robertshaw hi-flow thermostat with three 1/8" holes drilled in the cone. I tried more/larger holes in another stat and I couldn’t build any engine temperature in cooler weather. The 3 - 1/8" holes seemed to be the best mix, at least in my application. I've done away and plugged my pump bypass line; hence the t-stat drilled holes. The rest of the cooling system's well up to the task.

Here are my thoughts...

Without the pump bypass in operation I'm not recirculating water through the block/heads. The three holes in the stat just aren't moving enough volume of water to get a good block/head circulation and "blending" of engine water temps. This lack of circulation is causing localized hot spots in the cooling system to develop (probably heads). This is why I'm getting the massive temp spikes and steam hammer before the stat finally opens. My concern is with the temp spikes come excessive momentary coolant system pressure spikes too. With the "fragile" FE intake gaskets this is not a good thing. I'm good thus far but don't want to continue tempting fate.

Here's where I ask for help..

Since lack of cooling capacity isn't an issue I'm inclined to reconnect the pump bypass, as the factory intended. This should restore proper engine coolant flow. Is my thought process sound? What would you guys do??

Dave

Dave,

You have already answered your own question.



Bill S.

So Bill.... reading what I think your saying, you agree??

In addition, I'm looking for similar experiences to add a little self validation here too...

Use the Bypass.

Dave, I'm in the process of building my first FE and after reading about thisa subject here and over on the FE forum I decided to use the bypass hose. At the very worst it couldn't hurt.
It also sounds like you may have a sticking thermostat. Do you have a matched housing and intake for the thermostat size? Don't really know if I said that right; but do your intake opening, housing opening and thermostat size match? I didn't even know that could be an issue untill about a month ago.
What intake gaskets are you using? I went with KCR's and they fit perfect on my Ed heads.

Steve

The thermostat's fine, this has played out with three different thermostats all producing the same symptoms. The housings are all a match. I'm running the 2 x 4 Tunnel Wedge with Keith's custom gaskets for his stage II heads (much bigger ports than any OEM gaskets).

I would appear with only 3 little holes to permit circulation the coolant is allowed to become far to "stagnant" in the system. Hot spots are developing before the heated water can make it to the stat's thermo-bulb to enable stat opening.

Yes, use the bypass, Ford put it there for a reason.


Bill S.

Wouldnt a balanced t-stat help. check out www.performanceunlimited.com

Possibly, but I don't think so.. If the hot water can't make it to the thermostat, no matter how good/accurate the thermostat is it isn't going to open. My problem lies with the inability to circulate and get the hot water to the thermostat quick enough. After I get the flow right I'll then scrutize the thermostat a little closer. I honestly don't think I'll need to mess with it.

I blocked the bypass and have three 3/16" holes drilled in the t-stat. Just takes a little longer to warm up. No temp spikes and works fine.

http://i151.photobucket.com/albums/s...d/IMG_0251.jpg

I have the bypass hooked up with 1 hole in the stat (I think 3/16) as per the ERA manual and have no problems at all.

If the bypass is available and accessable what is gained (on a street driven car) by not using it?

That coolant that is constantly recirculated though the pump bypass does not pass through any sort of heat exchanger. If you plug that hose the water that once was recirculated without heat exchange is now forced to go through the radiator and benefit from heat rejection. By plugging the bypass you marginally increase the heat rejection capability of your cooling system. In my case the expense of doing so doesn't provide sufficient justification for the plugged bypass.

I questioned Robert Pond about his plugging the bypass on my engine ( Ponds 482 ) that he built for me . He said no problem and prefers it that way . Yesterday it was low 90`s here and at idle in the garage and only the car fan, 180 to 185 degrees max . It goes up smoothly with no surges or overshoot on the gauge . Are you sure you have all the air out the cooling system as it can a real bear to do ?? Stupid question ... are the holes on your thermostat on the top at 12:00 o`clock ?

Bob

Per MRG tech, The holes were installed at the top (12:00) of the spring housing that's inside the basket.

in my 351 block i had an oem 195 deg thermostat with holes drilled top and bottom and the temp would fluctuate too much and reach too high a temp on initial startup before it would settle back. switched to a stewart 180 deg high flow thermostat from speedway with holes drilled and at 70 deg. light cruising temp would be 150, get on it and temp would rise to 180 nicely. might be something to check out.

http://www.stewartcomponents.com/tec...ech_Tips_3.htm

I drilled mine in the same location as theirs, we musta talked to the same MRG tech guy..:LOL: