38 Top Gun Cooling Problem

[MERPerformance]

548 cid N/A Gen VI blocks, Proflier Heads, proper head gaskets, water cross over w by-pass, 142 degree thermostats, 20-30 psi water pressure, starts bouncing about 5 psi at 5500 rpms up till 6000 rpms, temp at 150 @ WOT, transom mount water pick-ups 8" up from center, have also installed Mercs 30 psi water relief dumps before sea strainers. What happens is above 5000 rpms cylinders 1-7 start getting hot and if you hold it, the paint will burn on cylinders 5&7 around the exhaust port and cause the gasket to lose qwench on the gasket at the water ports coming from the block to the head, the water ports by the front dowels are blocked as suppost to be and the rear dowel water port exits at the lower small one,these are the same gaskets used on the 525 efi they allow more water to flow around the the exhaust port. Ran these engines on the dyno with no problems I mean ran them hard! 165 degrees of water temp with extended run time. I can't understand why, the 1-7 cylinders are having this issue, the bouncing pressure is it coming from the affect of the water pressure relief dumps? I used these dumps only one time before on a 41 Apache with 1100. ANY THOUGHTS

[Sean Stinson]

Is it a step bottom boat?????

[Sean Stinson]

From the sounds of it that probably isn't the problem!!!! Are these the same relief dumps on GR????

[MERPerformance]

Sean, non-step. The water pressure is not steady,even in flat water, it floats and the dumps are not open at 4000 rpms. The pick-ups are adjustable and I lowered them again 1/8" Can you get a air pocket even with 30# water pressure? Why, would it only burn the paint above 5500rpms. No obstructions in blocks or heads, have never had anything like this before in any other boat. pick-ups on other set-ups have not been as of aggressive as these, do I switch back to the drives as a water source they have side and a pick-up in the nose,but the volume will be decreased

[MERPerformance]

Haven't talked with Greg, yet. I'll try again today.

[Ratickle]

My opinion, Start with the simple stuff first.

If you've never set the pickups this high before, or never used this style before, go to what you know has worked in the past and see if that's it.


Have you used this exact same crossover setup before?


And you have used this same pressure relief system before?

[MERPerformance]

Plenty of times. The pick-ups are not high, they are pretty low. and you are right on going back to the original set-up. The bad thing is this thing came in pretty messed up, engines to rigging, I really hate to remove pick-ups in place to use drives being the engine are 775hp have rigged plenty of boats and built alot of engines over the last 20 yrs,nothing really different except this problem with the 1-7 bank. I know people have problems with cross-overs and thermostats, crap in the blocks which block the water flow,but, this is not the issue I have check those items before getting on here and asking. never had to run bleed lines on the back of engines, gaskets come the same man that makes all of Mercs. HP stuff I know those patrs are correct, Ihave never burned the paint on an alum.head around the exhaust ports and the temps on the dyno were higher and with regular headers.

[Chris]

Can you walk through each piece in the system, from the transom pickup through where the water exits? Also, pics might help.

I'm thinking there's a restriction somewhere causing pump cavitation. Since you ran it on a dyno, clearly you have rigging issues.

[BUIZILLA]

EFI or carb?

if it's carbed, dual plane or single plane intake?

[Ratickle]

Probably a dumb question, but.

Since 1 and 7 are both port side of engine, any chance the header jackets are plugged on that header and the heat is actually transferring from the header back to the head?

[MERPerformance]

Nothing really different on the system from anything else I have done. Pick-ups, sea strainers, oil coolers, cross-over kits, running with thermostats or without, except a restrictor plate. #10 by-pass hose instead of the # 8 they send, this includes the sizing of the fittings to match with no restrictions. Its a carb single plane, The header is not restricted CMI with # 12an hoses, no hot spots. The thing is the pressure bounces about 5-8# above 4000rpms. 20-25# @4000, 5500-6000 25-30# bouncing 5-8#, but the hull is running flat on flat water in the ICW, would think air is being picked up off the hull on a 99 non- stepped bottom, the water dumpsfrom Merc are not even open at 4000 and they are progressive opening before they reach 30#. I had a 2004 topgun with big oil temp issues that we fixed, but we modified the sportmaster lower and added air dump lines off the sea strainers from Marine Machine corrected the oil temps, the the engine had no by-pass, just cross-overs with restrictor plates, those engine were running 320 in the pan and they came down to 250-260. This set -up is running about 220 steady running with thermostat controlled.

[BUIZILLA]

is it possible the intake hose interior is deflecting??

[MERPerformance]

This happening on both engines, all the hoses are new, quality Sheilds Flex. Guys thanks for your thoughts on this, think about it. I have to go in and finish machining some heads for another 38 and get them on the dyno. I'am going to try Zul and Lipship monday maybe the have had this in the past. I really would hate to go to the drive for water supply due to the restriction in the hose size in the gimbal, we are using the drive for cooling it's self, with # 8 lines off the side of the water jacket on the upper instead of the cav. plate. I'll check back tonight. Thanks again! Mark

[MOBILEMERCMAN]

Is it possible there is air entering at the pick up? A burr, a little caulking? Have you verified there is no air running thru the motor. Temporarily installed a clear hose between motor and headers and extend to cockpit to allow visual confirmation.

Like Buzilla asked. Are you using Braided hose in front of the sea pump?

The water entering the boat is under high pressure so a little air bubble can expand once it enters the engine. The gauge cannot tell if it is water or air. If it is fluctuating I would be looking for air.

[Ratickle]

Both engines are doing the exact same thing with the exact same cylinders???

What would they have in common that is different than any other setup you've done in the past? Only the bleedoffs and the pickup?

[Sean Stinson]

Mark I ran into this with a 42' Tiger with Big Power 1000+ HP and what the problem was is that the water pick-ups were too low and what was happening was that when the water entered the pick-up at high speeds was that it was creating a vortex maelstrom or whatever you have and it was creating an air pocket or turbulence in the pick-up thus creating steam pockets....it would burn the paint off of 3 and 5 on the head and when I stepped on it with a barefoot it burned the $hit out of my foot on the valve cover. If your valve cover is that hot that is bad!!!!!! Very Bad!!!!! Oil temp would climb to temps approaching 270-300 which was also bad....Anyway you already know all of this raise the pickup to about 3/16ths and see what it does that is where your problem is coming from I am sure of it!!!!

[MERPerformance]

Sean, thanks for posting this after we spoke on the phone yesterday, it makes sence of my problem. Why this only happens on the odd # bank is werid, I have gen 6 blocks and I'am sure you had either bowtie or dart blocks which use a different gasket. Wewill see what happens after I get the gaskets in from my supplier.

[Geronimo36]

How old are the blocks? I once had a big chunk of rust get stuck in an engine and it was effecting water flow. But you say it's both engines so I'd go with Sean's line of thinking on the water pick-ups.

#7 always seems to run hot regardless and is always the first to detonate if there's a fuel problem. The bleed lines off the rear of the intake will help with that.

[MERPerformance]

The water-pickups are from Stainless Marine Square tube with 6 mounting holes, they are down 3/8"below the hull and 8"out from center.I believe Sean, is right. What concerns me is I spoke with Jerry, @ Stainless Marine, now they are telling me it's better to use their HIGH SPEED pick-up! The bad thing is I ordered these from them telling them they are for a 38 top gun with 775-800 hp. Not real happy about that, sure the customer won't be either. Going to raise them up to 3/16" and go from there. This one project has not been fun! But;you can't quit. Let you know how it turns out.

[Blue Thunder]

It sounds to me like the timing is retarded and you are blowing the flame out the exhaust valves. Just a thought.