Thermostat and Throttle Valve

[Chris J]

I was reading the "water in oil" and noticed several recommended adjusting the valve between the pump and motor to control temp. I've been running my valve wide open and letting the thermostat control the temp. What are the advantages of controller temp with the valve? Why wouldn't you let the thermostat control temp?
Pumbing on my BBC is as follows:
1) Water from pump runs through oil cooler
2) From cooler it tees off to water pump mounting holes and front of logs (Glenwood)
3) Comes out through thermostat and tees in again with front of logs.
Thanks

[sleekster]

i don't think one is better than the other except the thermostat set up is a little more costlier and well probably more consistant.

[Mohavekid]

Most of us don't run a thermostat and the only way to slow the water down thru the motor is to control how much is allowed in, via gate valve.
It also helps to control water pressure from the pump to the motor. Too much pressure from the pump can cause blown head or intake gaskets and cause watyer in the oil. All bad things.
If your setup works for you, leave it alone.

[jim@pj]

You know, I have been arguing with my customers for years about factory water valves. In the early seventies these valves were used as a cheap way to control engine temp. Even today most jet boats have them. Over the years I have found that they can do more harm than good. When you turn a water valve down you reduce the volume of water to your engine. A number of things can happen if you are not careful. First,with the reduced volume the block runs cool but the heads run too hot. You can crack valve sets ,tulip valves and even detonate your engine. Oldsmobile motors are notorious for this. Secondly, with a valve, your engine temp usually fluctuates too much from idle to W.O.T this can lead to more cracked parts. The dual acting thermostat systems work great because you will always have full water volume to your engine and the temp fluctuation is reduced.In my opinion the water valve should be replaced by a pressure relief kit. Too much pressure will blow out gaskets especially at the intake manifold water jacket cross overs, hence water in the oil. Olds motors are especially troublesome here. If your jet is built then the problem becomes even worse. With some of the High performance customers I have, two relief valve systems are used.. You only need 12 psi not 80 psi. The 460 ford does not have a dual acting thermostat kit available so we set up our own thermostat systems.
Its true that the water valve has been around for a long time and working for some people but I have worked with alot of folks that have had major problems. Again it is true that the valve is cheaper, but with jet boat engines, going cheap can cost you a lot of money in the long run. I sell the pressure relief kits along with thermostat assemblies. Its good insurance.
I rest my case. Jim www.performancejet.com (http://www.performancejet.com)

[LVjetboy]

Chris J,
Just curious, if you already have a thermostat, why would you even consider trying to control temperature with a valve? I also run a thermostat as you do.
If you don't run a pressure relief as jim suggests, then, depending on your power level, you can exceed normal coolant pressures at full throttle without some way to control pressure too. And, depending on the condition of gasket seals, some engines will be more sensitve to pressure than others. I use a valve to control full throttle pressure (NOT temperature) but there is some debate as to the risk of reducing idle flow. My engine's been pretty mild so far...soon to change. As you go up in hp, reducing full throttle pressure with a valve may cut idle flow to the point that hot spots develop...not a good thing.
Although I doubt anyone can tell you where this hp point is or what the risk of hot spots is for a given flow rate and temperature, a pressure relief valve will at least allow full flow at idle...such as it is. Idle flow and pressure from the pump even with no valve is pretty low. The ideal system may be some sort of booster pump to keep temperature lower (and pressure higher) at idle. Never seen one though.
Jim, what is the "dual acting" thermostat kit you refer to? Is it different than Rex's thermostat kit?
jer
[ February 09, 2003, 02:01 AM: Message edited by: LVjetboy ]

[Taylorman]

Jim referred to a pressure control valve, if I understand the Rex thermostat correctly, it has a pressure valve in it set at 15 psi which dumps water overboard when pressure reaches this point. Why would you need another pressure relief valve?

[LVjetboy]

Taylorman,
The Rex thermostat does have a bypass valve which helps regulate pressure when the thermostat is closed. With some engines, you can overpressure your seals if you have enough hp to put out high bowl pressures. Or you may have weak seals. With your 455, I doubt you need to worry about high hp and all this may be a mute point.
I've seen 35+ psi at full throttle with my mild 454 turning a B at 5000 rpm. Now that mild hp may not leak "good" seals, but my worn seals now leak at anything over about 15 psi. Power level and seal condition are important points, and one reason you'll see different opinions about what pressure's acceptable. What works for one may not for another. But if you at least have a pressure gage, the answer is clearer.
A separate pressure relief or regulator can also control pressure. As your hp goes up, a pressure relief or regulator may be better because an inlet valve may restrict idle flow too much. For most jets, a valve works fine. Now worries. But as power goes up, other ways of controlling flow should be considered. Does that make sense?
jer

[jim@pj]

You guys are all think'in... I like that ...When i refere to the Dual acting thermostat I am referring to the Rex type assembly. It is true that the spring loaded check valve does relieve pressure shock when the thermostat is closed but I believe that the main reason for the valve is to keep water runnig to your exhaust headers or risers. If you didn't have this valve in the thermostat assembly water would be shut of to your exhaust when the thermostat is closed. Thats bad..The pressure relief system is plumbed in before the engine inlets thus reducing the pressure spikes even further when the thermostat closes. Make sense? When the boat is idling the pressure relief won't be opened and full volume and pressure will get to the motor. Agreeed, it will be less pressure and volume but it will be flowing thru a full size water way with no valve.
By the way , it is best to have a 3/4 inch line coming fronm the jet to reduce friction losses. At the water tee the 3/4 line is reduced to 5/8 lines to the front of the motor. Thanks for the fed back guys Good Luck Jim