PurdueCAT

I plan on getting rid of my automotive style water pump on my 502's and was wondering the difference between running a crossover setup that uses a thermostat vs. on that does not. Thanks in advance.

Craney

Are you fuel injection or carb?

Warlock98

Not trying to jump your thread but I am wanting the same advance. how do you hold engine temp without a thermostat

Griff

If its basically a stock engine, then I'd leave stock recirc pumps.

If its modified substantially, then I'd run crossover with a Tstat and bypass.

PurdueCAT

Carbed. I had 500's but I'm going bigger and wanting to get rid of the automotive style coolant pumps on the front. So looking at crossovers, I'm trying to make an educated decision on weather or not to go with the thermostat or not. It makes sense to me to run the -stat to get the engine to operating temp, but what is the purpose of running without one?

brian41

We run circulating pumps and thermostats on all our engines so that block has even temp weather its a EFI or carb engine. How many engines does Merc run with crossovers?. Found out 20 years ago about hot spots caused by crossovers and never looked back.

PurdueCAT

Interesting. I'll make a note of this.

Budman II

Purdue, I just got off the phone with Bob Madara after a lengthy conversation discussing things from valve train geometry to the need for 4-corner cooling on intake manifolds, and circ pumps versus crossovers and the use of T-stats is one of the topics we discussed. To paraphrase what Bob said, you should always run a T-stat to control the block temps as much as possible. In an internal combustion engine you have to have a stable thermal environment (as much as possible) for efficient operation. If you have block temperatures varying excessively from the front of the engine (with cold lake water going in unimpeded) to the rear where the water has been heated up, you may have problems with front cylinders scuffing because they are too cold, while meanwhile you have pockets of excessively hot water in the rear of the engine causing bad things like valves sticking in the guides, detonation, etc. I'm not going to claim to be an expert, and hopefully I have accurately paraphrased what Bob told me, but that is what I understood the risks to be of running no thermostat in a marine engine with raw water cooling.

BTW, if you decide to go the crossover route, I might be interested in one of your circ pumps if they are marine versions and are low hours.

Good luck!

PurdueCAT

This isexactly why I asked, because I couldn't see a reason why anyone would run without one either.

Budman II

A friend of mine is running a crossover on his HP500 clone. He switched from a circ pump mainly because he was running a roots supercharger on it for a while. I remember when he switched that it took him a while to get things ironed out. He ended up having to employ a pressure regulator and a dump through the transom to regulate block pressure. I also think he went with a standard T-stat, but had to drill a couple of holes through it to keep it from cycling constantly. Pretty sure there are multiple threads related to that on here.

I thought about going to a crossover just to clean up the front of the engine and cut down on parasitic losses, but did not want to deal with all of that. The circ pump has always worked fine on mine. I really don't think the pump itself does very much as far as moving water through the engine - I think it really just moderates the flow. In fact, I was running a standard automotive pump on my last engine for many years, and eventually the non-stainless vanes rotted away. I never noticed any real change in operating temp at all - the only thing that brought my attention to it was the sound that the edge of one of the vanes was making when it scraped the inside of the housing! I really think you could just run a "dummy" circ pump with no vanes and it would work just fine - very much like a crossover.