Holman Moody 302 thermostat question

[frclarke]

Some of you know I've been restoring a 69, 16 with all the original stuff - Sugar Shaker. I got back the final piece last night - the Holley 650cfm carb. According to the rebuilder, this thing is from the early sixties. They did a wonderful job and it looks brand new. I had them put in J tubes for the Coast Guard and an electric choke for me.
I fired her up - WOW - What a feeling after a year and a half of work. The sound is so different from the modern engines. The vibration through the boat puts you on notice this thing is ready to GO. The old boat engines are solid mounted to the stringers.
Its fairly cold up here - so when cooling water hit the hot manifolds a vapour mist rolled out and around the boat and through the shop. Surreal...
Anyway, there's still lots to do. One big thing is the engine is not warming up. When I redid the engine ( feels like a decade ago) I drilled out the bypass hole in the thermostat housing to 3/8". Clearly this is too big. The stat is staying closed. Anyboby know what size this should be?
I intend to put in a brass threaded plug and drill it to the correct size.
Fred

[MOP]

Frank 3/16" I would go to 3/16" that may do the trick if not you can drill it a tad. Was perusing the 1K pics last night to use one as a screen saver and was wondering what you were up to.

Phil

[frclarke]

Thanks MOP:
half the size eh:canada:
Fred

[Tim Morris]

Its fairly cold up here - so when cooling water hit the hot manifolds a vapour mist rolled out and around the boat and through the shop. Surreal...

Where's the video?

[MOP]

Eh I think it will work:yes:

[JimG]

I struggled with the same thing with my HM 351W. Low temps... I tried everything, still read low. See this thread, I finally stopped worrying about it. Four years later, still running strong...

http://www.donzi.net/forums/showthread.php?t=1436&highlight=351w+temp

[f_inscreenname]

Like a car that warms up in the driveway you will never get it up to operating temp until it's under load. I would take it for a ride before I would start changing things.
And yes those old motors do sound real good.:yes:

[BigGrizzly]

I have seen this many times before guys trying to clean out the bypass. some people have removed the t-stat and actually the gage reads over heat. Sweet 16 did this than pyt it back to normal and runs fine. The guys are correct you won't see above 160 in the drive way. Fred call if more help is needed.

[mphatc]

I gotta thow my 2 cents in here . . as my old original 302 H&M and the new one exhibit the same symptoms . . inadequete temp. For me this means pistons aren't matched to the bores and over time it gives you premature engine wear . .

Even with swapped t-stats running both an old and a new wax style. NO difference. I was able to get a warm engine in 73 degree water at idle . but not at speed!

There has to be a proper pressure for the system to run at and then bypass . . the Johnson pumps will build huge pressure as they are a sealed impeller, a conventional circualtion pump will not build alot of pressure.

Mario L.

[BigGrizzly]

I have two different H&M cooling systems on my 16, orig 289 (now 302), and the 351 Cleveland. Both have Johnson impellers, now. Just because they were easier to get locally. Since nothing else will fit in the original place the H&M pump. I did not have any cooling problems when stock raw water was used. I did not modify the system at all until I put a closed system on both boats with stock H&M raw water pumps. One strange part id the 16 has lower unit pickup and the Corsican has a transom pickup. i€ have always run a 180 t-stat in the engines. The 16 came with a 140 or 160, can't remember which now (we bough the 16 new still have it). I put the closed system on the 16 after the timing change cover rotted out because of salt. I machined out the cover and pressed in a brass cylinder and O-ring grooved it too, just because I could, and my grandfather said I should (read that had to). Anyway I think the key is the bypass. I do realize the have Johnson pumps with more out put but only so much water is going to pass the T-stat.. One thing I did find out, if the bypass in the 351 Cleveland is enlarged the unit will over heat. This is only in that block, not the 302 or 351 Windsor. Another point when power trim is used the lower unit water pick up is at the wrong angle when trimmed high and motor over heats. Rember on these boats the water inlet is 3/4 inches id.

[boatnut]

I've been running a H&M 302 (without an overhaul??) for about 37 years and it always ran cool (especially if the water was cold like Tahoe or SF Bay). In
'73/'74 we had a Magnum hull with two 300HP Chris Craft engines (LT1 eng with Volvo 280 drive) and played around with it in production offshore. Those engines ran cold also. CC said they had to be setup to run between 140 and 150 because when you get hotter the salt drops out of solution (all raw water cooled). I know most on this forum prefer to not run in salt with raw water cooling but I did it for many years and never had a problem with corosion --none. We always flushed the engine prior to putting the boat away. I know closed systems are best and then you can get to a better temp, but thought I would mention the temp vs salt issue. Ed

[JimG]

'Poodle, I agree. I forgot to mention that I shot my oil filter with a temp gun after running hard: When the water temp showed barely over 120, the oil temp was around 180. Made me feel better.

[MOP]

Being an old marine tech my thought would be with a standard setup IE no cross over why not run a Merc Tstat housing, there were no temp issues the Tstat always worked and brought the engine up to proper temp. I highly agree with Mario if the block temp is low the parts do not come up to tolerance promoting premature wear and reduced efficiency.

Phil

[BigGrizzly]

Phil several auto companies have run wear tests on cold engine temps. Honda did but their engines aren't relative do the RPM ranges. However the one that GM did was published and it stated that engines running lower than 160F T-stats would have a increase wear of about 40%. I read The SAE paper several times. After we did our tests to confirm and holy cow was it scary. Remember the old days of sludge in engines. Our tests showed too hot is better than too cold. I realize salt is a issue but not as bad as it is stated. With closed cooling systems I can run the engine hot and exhaust temp cool.

[JimG]

Our testes showed too hot is better than too cold.

Ouch!:eek:

[vonkamp]

LOL, I caught that typo but refrained...:smash:

[BigGrizzly]

Spelling was never my forte. Oh well!! I will go back and correct it teacher. Amd since I can't spel,l it I will look it up in the dictionary.

[JimG]

Just pickin' on you Randy! That was just too good to pass up...

Take care, and Happy Holidays!

Jim

[BigGrizzly]

JinG no problem I can live with my mistakes, plus it was funny. Sense of humor I have , but spelling is more difficult for me the Calc II and statistics combined in college.

[frclarke]

Just to "finish" off this thread, after reading through and considering all of your great input I did the following:
From MOP - I reduced the bypass hole by 1/2 - note that by reducing the hole size by 1/2 the area of the hole is reduced by 4, this means that flow is reduced probably not by 4x but certainly more then 2x.
From Poodle - I checked the manual (DUH!), specified T-Stat temp is 150 - can only get a 140 as Poodle indicated.... so I installed a new 140 Stat .

THE RESULTS:
With the boat on the trailer all warmed up.
Temperature guage reads approx. 130. ( Before, the guage would'nt even move)
When I shoot the manifolds with an IR gun, temperatures are running 172 - 180 steady.
When I shoot the Oil filter it is 126.
When I shoot the block it's 126.

Not bad :),
I'm a little worried about the temp. of the manifolds - I'm betting that when the stat opens up the manifold temps will come done.

Chances are pretty good that I'll end up having to open up the bypass.

Hope others find this useful.
Fred

[glashole]

so when do we get that invite to come up and run with you guys in your neck of the woods?


:)

[BigGrizzly]

Don't worry about the exhaust, it will actually cool down a bit when running so to more flow.