Blown Head Gasket??

[Sandbank]

Wondered if anyone could help...I can see the end of my tether from here!
Issue: Do I have a blownhead gasket or could it be the heat exchanger and what is they way to tell without changing the head gasket?

Problem: Engine overheats: gradually the temp rises (faster at revs (like 6 mins at 3000) until overheats. Manifolds get hot early and just get hotter.

Background: 2nd handboat and have had nothing but issues!!
GM smallblock V8 with Alpha 1 Gen II stern drive.
Freshwater cooled via heat exchanger.


Investigations and works to date:
Original overheat probably caused by SW pump impellor.
Mechanic reported cylinder pressure 140 on all bar two cyl that had 125PSI- he considered not head gasket and did not replace and just did SW impellor-problem not fixed.
I have back flushed the entire system in case parts of impellor in lines.
Checked engine driven water pump and all good.
Not the thermostat as was removed.
Clear and free flowing water throughout both closed and SW system when back flushing.

The heat exchanger tends to buildup a bit of heat on the way to the overtemp but the manifolds roast. Flushed the whole heat exchange and good unrestricted flowthrough the system.
Last time overheated the holding tankcap let the pressure off (and the coolant!)

After reading lotsa iforum posts I am thinking the headgasket blown and causing blow back that is restricting the coolant closed loop?
Is there a way I can confirm this without the major works of a newhead gasket (or head) so I know for sure?? Thishas been driving me crazy...
Thanks

 

[etracer68]

Re: Blown Head Gasket??

I would think if you have a head gasket leaking into the cooling system, you would be getting high pressure in your closed cooling system. On an auto motor it will blow the coolent out if the cap is removed while warming up the motor. Think of it this way, compression from the cylinder in question will pressurise the closed system. Just my opinon if the head gasket is leaking in a water jacket.

 

[tpenfield]

Re: Blown Head Gasket??

Recently been there, done that . . . If you want hit the link in my signature to my web pages that document my engine rebuild. It all started out with chronic overheating and nothing seemed to fix it.

I suspected a blown head gasket and did a cylinder leak test. It showed more valve issues than a head gasket. your results will probably vary.

Anyway - cutting to the chase, it turned out to be a combination of 2 things - (1) some barnacle fragments solidly lodged in the cooling intake line going from the outdrive to the transom plate, and (2) the engine block was reasonably filled with sand. Sand is probably not the case with your engine, unless the FWC was a recent conversion.

Let the cylinder leak test be your guide, 2 'bad' cylinders right next to each other would be a strong indication of a head gasket issue. Also air bubbles coming into the cooling system when cranked or even running.

 

[scoflaw]

Re: Blown Head Gasket??

Sounds more like an exhaust manifold and riser problem. I would look there first.

 

[Bondo]

Re: Blown Head Gasket??

Issue: Do I have a blownhead gasket or could it be the heat exchanger and what is they way to tell without changing the head gasket?

Ayuh,... Beg, borrow, or buy a Stant cooling system tester, 'n Pressure Test the freshwater side of yer system....

 

[Don S]

Re: Blown Head Gasket??

1. Does the engine overheat if you keep it below 3000 rpm?

2. Is your exhaust manifolds part of the closed cooling system?

3. Have you checked the exhaust elbows to see if they are plugged up?

4. Put the proper 160? thermostat back in.

5. To check the head gasket properly, top off the coolant in the heat exchanger, leave the cap off so you can see the coolant.
Then bring each cylinder up to TDC on it's compression stroke and pressureize that cylinder like you would in a leak down test and watch for air bubbles in the heat exchanger. If you get bubbles, you know which cylinder is leaking.

 

[Sandbank]

Re: Blown Head Gasket??

Thanks Guys, I really apperciate the input and advice.
In response to the last post:
1. Does the engine overheat if you keep it below 3000 rpm? Yes but takes longer

2. Is your exhaust manifolds part of the closed cooling system? Yes it is part of the closed loop.The SW only enters at the top of the exhaust riser then out via exhaust air and water

3. Have you checked the exhaust elbows to see if they are plugged up? Checked a few months ago, but excellent though as really the only part of the SW system I have not really physically inspected or directly flushed.

4. Put the proper 160? thermostat back in. OK

5. To check the head gasket properly, top off the coolant in the heat exchanger, leave the cap off so you can see the coolant.
Then bring each cylinder up to TDC on it's compression stroke and pressureize that cylinder like you would in a leak down test and watch for air bubbles in the heat exchanger. If you get bubbles, you know which cylinder is leaking.

Unfortunately...the holding tank is high and cannot view inside the cap-doh.

Will do a pressure test I think to see if leakage back into the cylinder.If there is then a gasket. If not then will have a peek at the risers....

 

[Sandbank]

Re: Blown Head Gasket??

Re whether overheat below 3000 rpm, really only gets to around 1/2 to 3/4 temp on the gauge if I keep it at idle. Dont know what this indicates?...

 

[Pete104]

Re: Blown Head Gasket??

When the impeller was replaced, was there a new pump kit installed? More often than not, a new impeller in an old housing will cause this.

 

[etracer68]

Re: Blown Head Gasket??

Don S, is correct on the smiple way to check. I may add that the piston can be any where on its compression stroke, you can take the valve cover off to make sure the valves are in the closed position too.

The part Im not understanding is, why cant you see inside the exchanger while the cap is off? If you ever had to add or check coolant level, you had to be able to see it.

 

[Don S]

Re: Blown Head Gasket??

I may add that the piston can be any where on its compression stroke, you can take the valve cover off to make sure the valves are in the closed position too.

No it can't, the pressure will push the piston down to the bottom of the stroke and start opening the exhaust valve.

Unfortunately...the holding tank is high and cannot view inside the cap-doh.

I am referring to the heat exchanger tank, not the recovery tank. Can you post a picture of heat exchanger.

 

[Sandbank]

Re: Blown Head Gasket??

New hosuing was installed with the impellor as was cracked. Also the other day I by passed the SW pump during testwith fresh water under presuure to take the SW pump out of the equation out of interest... still overheated.

As for the top up tank...The cap is up under the gunnels and whilst I can just reach to top it up cant see in;the level is checked via a side mounted sight tube-hope that makes sense

 

[Pete104]

Re: Blown Head Gasket??

Have you had any A/F in any cylinders? Have you done a leak down test? When you pulled the risers to see thier condition, were the flappers in place?

 

[rdranman]

Re: Blown Head Gasket??

I was less fortunate than you in my rings were shot after similar issues with a big-block. When I took the boat
into the shop, I let them pull one of the exhaust manifolds off. Man-oh-man... you could hit the mainfold on the ground
and a cup of rust would fall out, hit it again and another cup, and so on and so on... I suspect that some of your
cooling ports in the exhaust maifolds are probably clogged and so you are only getting partial cooling (would still allow
SW to flow through the other ports falsely inplying there was not issue with them. Would be worthwhile checking.

 

[Sandbank]

Re: Blown Head Gasket??

Guess I need to check the exh manifolds (and flapper as to be honest cant recall seeing one!). Then move to a leak down presure test.-Thanks heaps guys. The boat was a full reno job by previous owner and I am still trying to unravel through his work...or lack of!

Don S-the way the system is setup there is a holding tank and a seperate heat exchanger-made in UK cant remember the brand but no way to see inside without taking the end plates off and dismantling (Seemed to be good clear flow through SW and coolant loops as per original post). The holding (topup) tank has a feeder tube into the outflow part of the coolant loop. Its not the conventional type H Exch with the topup tank on top.

 

[Sandbank]

Re: Blown Head Gasket??

Mine only had a bit of rust where there had been some backflow around the SW exhaust inlet at the elbow, probably where tap water had not been turned off soon enough on flush out and had dribbled back down I suspect. Ran a mirror and light into the core and the inside looked OK in the exhaust area. Really impossible to check inside the coolant jacket though and no way I can think of to isolate the area. The fact same heat on both manifolds.. leads meback to heat exchor head gasket...Thinking out aloud, I could pump fresh tap water into the coolant inlet(s) on the manifold and just let the thermostat outlet pipe (into the bilge), getting a bit hazardous though in case water levels ran low and system would not be pressurised - not sure that would actually prove or disprove anything though...