Penta Md2b overheating, advice needed, maybe need engineer local to Barry

[Andy92]

Hi all, I’m new to the forum and to forums in general so apologies for mistakes and if posted in the wrong place, I posted it here because the boat is kept at Barry island.

I know it’s been covered but just looking for advice with regard my exact scenario and weather it would seem pointless to carry on with my current approach.

I’ve recently purchased a new to me westerly centaur with an aged Penta MD2B which starts first turn of the key and seems to be a good engine over all. Unfortunately however I recently ran it for an extended period of time for the first time after changing the impeller and thermostat (as a precaution) and the cylinders are overheating can’t even touch them they got so hot.

There’s a good flow of water out the exhaust however I presume the coolant passages round the engine were so blocked no water was going round the block.

I’ve Taken the exhaust manifold off and poked about with coat hanger wire, then directly injected bicarbonate and vinegar (gentle approach), then holts speed flush from Halfords, then oxilic acid and let it sit overnight. I injected this with a syringe straight into the ports on the side of the block after removing the exhaust manifold . The result is the rear cylinder now runs cool as it should, but the forward one still runs hot.

I have been advised to try brick cleaner which is a bit stronger and intend to do this as the next step. Failing that is there anything else I can do without removing the head ?

If it comes to having to remove the head I would be looking for a mechanic to do it for me I think as I am not too confident about that step and also in a rush to get the boat in the water.

Any help is much appreciated.

Sorry for the essay I struggle to be concise

May be embarrassing if I have posted this in the wrong place

Cheers, Andy

 

[VicS]

Hi all, I’m new to the forum and to forums in general so apologies for mistakes and if posted in the wrong place, I posted it here because the boat is kept at Barry island.

I know it’s been covered but just looking for advice with regard my exact scenario and weather it would seem pointless to carry on with my current approach.

I’ve recently purchased a new to me westerly centaur with an aged Penta MD2B which starts first turn of the key and seems to be a good engine over all. Unfortunately however I recently ran it for an extended period of time for the first time after changing the impeller and thermostat (as a precaution) and the cylinders are overheating can’t even touch them they got so hot.

There’s a good flow of water out the exhaust however I presume the coolant passages round the engine were so blocked no water was going round the block.

I’ve Taken the exhaust manifold off and poked about with coat hanger wire, then directly injected bicarbonate and vinegar (gentle approach), then holts speed flush from Halfords, then oxilic acid and let it sit overnight. I injected this with a syringe straight into the ports on the side of the block after removing the exhaust manifold . The result is the rear cylinder now runs cool as it should, but the forward one still runs hot.

I have been advised to try brick cleaner which is a bit stronger and intend to do this as the next step. Failing that is there anything else I can do without removing the head ?

If it comes to having to remove the head I would be looking for a mechanic to do it for me I think as I am not too confident about that step and also in a rush to get the boat in the water.

Any help is much appreciated.

Sorry for the essay I struggle to be concise

May be embarrassing if I have posted this in the wrong place

Cheers, Andy

The PBO Reader to Reader forum would have been the most sensible place. Your problem is not unique to the Bristol Channel and Reader to Reader is the place for all practical advice.

Dont duplicate your post though.... Ask the moderators to move your post or perhaps put a short post there with a link to this one.

I think you are on the right track . Are you sure you got all the channels in the manifold clear ?

Those old raw water cooled VP engines are a real pain when it comes to getting the water ways clear ( we had trouble with a MD11C 20 or so years ago.. and the MD2B is its predecessor. Its over 40 years old.

A sulfamic acid based central heating descaler such as Fernox DS 3 would be my choice for a less aggressive chemical than a hydrochloric acid based brick cleaner, or alternatively Rydlyme. To be effective though any acid cleaner needs to be circulated ( and with the milder ones also warmed ) If there is absolutely no circulation due to complete blockage of parts then you are fighting a loosing battle.

Heads off and blocks lifted off may be the only way. ( You do need the right type of piston ring compressor though to refit the blocks!)

 

[scottie]

The PBO Reader to Reader forum would have been the most sensible place. Your problem is not unique to the Bristol Channel and Reader to Reader is the place for all practical advice.

Dont duplicate your post though.... Ask the moderators to move your post or perhaps put a short post there with a link to this one.

I think you are on the right track . Are you sure you got all the channels in the manifold clear ?

Those old raw water cooled VP engines are a real pain when it comes to getting the water ways clear ( we had trouble with a MD11C 20 or so years ago.. and the MD2B is its predecessor. Its over 40 years old.

A sulfamic acid based central heating descaler such as Fernox DS 3 would be my choice for a less aggressive chemical than a hydrochloric acid based brick cleaner, or alternatively Rydlyme. To be effective though any acid cleaner needs to be circulated ( and with the milder ones also warmed ) If there is absolutely no circulation due to complete blockage of parts then you are fighting a loosing battle.

Heads off and blocks lifted off may be the only way. ( You do need the right type of piston ring compressor though to refit the blocks!)

Ideally you should be able to get a flow of water out the drain plugs and BE CAREFUL The gaskets under the blocks are actually shims and determine the bump height

 

[Andy92]

Hi VicS,

Thanks for the reply, I will do that, do I just copy the link from the browser and start a new post under the same name with the link pasted into it ?

The manifold is completely clear I think it’s quite a bit newer than the rest of the block as well, there is some sea-life growth near the thermostat housing end that the oxilic didn’t shift overnight but it’s wide open there so I’m not too worried, the small ports were blocked originally but now have good flow through them.

I will try persisting in a similar manner for a while if it isn’t totally hopeless then.

I will try the fernox first, I’m concerned as inevitably try as i might these chemicals seem to end up in the bilge and I have to swill it out fast so weaker is definitely better for me.

The circulation is good now I’ve prodded but not enough volume going in so must be well blocked round the cylinder, difficult to rig up anything that isn’t messy because the ports in the side of the block (under the manifold) aren’t tapped and I was worried about circulating it through the entire engine because then I think it will bi pass the localised problem ? Maybe a constant feed in the top and catch it in a bucket then repeat for hours and hours haha

Brick cleaner will be a last resort before the head I reckon.

May be out of my depth taking the head off, never done that before, suppose there’s only one way to learn !!

There was an unused crated engine on eBay recently for 2000 which I wasn’t financially ready to do at the time but now I’m wondering if that was a mistake and I should have bitten the bullet.

Thanks again for your advice it’s nice to know I’m on the right track

 

[Andy92]

Hi Scottie thanks for the reply,

Maybe I’m getting there I get a gush from the rear drain now where before it didn’t flow at all and the forward drain is an enthusiastic dribble !!

Do I have to be careful if I have to remove the head ? Is it easy to get a gasket that’s shimmed the same ?

Thanks for the help

 

[vodzurk]

Our ~35 year old VP ran a little too hot after extended peroids when we first bought her, to the extent we couldn't go faster than 8mph (depressing when planing speed is 15mph).

I don't know if any of this will be relevant to your model, but hey, I'll ramble on ...

We tried a few things, as below. Sheepishly, I suspect #1 was the resolution.

1. Top up coolant.
Our engine manual specified filling up to a certain point visible through the nozzle. Instead we filled up to the overflow and would just clean up the overspill.

2. Replaced water pump.
Our water pump leaked a bit. We'd have to clean an inch of water out of the bilge per hour of use. Engineer reckoned there wasn't any point changing the seals given its age and the unlikeliness of success. So we replaced it.

3. Clean filter.
Probably not much of an effect... only had a couple of "bits of fishfingers" in it. Also made sure it was properly fitted seated / slotted in afterwards.

4. Checked thermostat.
Wasn't at fault in our case, but mentioning it as it was suggested so many times as being the most likely candidate. An engineer checked it for us with a laser thermometer. Not too sure how... but I think he confirmed it was opening at an expected temperature and causing liquid to flow as expected.

5. Feeding Coca Cola to the engine.
This was my favorite. I tried to get rydlyme from Force4 but the guy on the counter had never heard of it. When I described it, he said something like "oh, that? We just use coke, works a treat". After some research (for example video linked below), it seems the Phosphoric Acid mayyy have a cleaning effect. However, most professionals I've talked to say it's ridiculous to use cola, that it won't have any effect. I aim to do this every season, and have done twice thus far:

(1) buy 5L of Coca Cola (with Phosphoric Acid listed as ingredient, as not all have it now).
(2) make a funnel out of a large bottle, disconnect seawater intake (I was shown how to do this by an engineer, and ours is above the waterline), duck tape massive funnel on.
(3) fill funnel with cola.
(4) shout for wife to start engine.
(5) keep topping up funnel until all 5L is guzzled.
(6) as soon as funnel is drained, shout for wife to kill engine.
(7) wait 24 hours.
(8) run for a few minutes to flush it out.

As I say, I'm not totally convinced about #5, but it's cheap. Some people also mentioned something akin to "rodding"... using wires or the like to scrape out the insides lose of gunk, though I never tried that.

Either way, good luck, it appears to be an elimination exercise. I hope you can get it sorted asap, as the weather has just turned fantastic!

 

[NotBirdseye]

Cola is regularly used as a cleaning aid, really good for cleaning toilets too. I say cola rather than coke because some people get really confused. (Coke is the name of many different items)

 

[Andy92]

Thanks for the reply vodzurk,

Sounds like many people have experienced this problem and got through it without it being curtains for the engine !!

The engine is still raw water cooled so no issue with topping up I did change the impeller however and have got good coolant flow.

The cola is an interesting idea I had considered it but couldn’t see how it would be strong enough, I will give it a go.

Think I’m going to run the fernox ds-3 through it for a while as suggested by VicS, if that doesn’t work go for the brick cleaner and if that doesn’t work try feeding her cola and let it sit !! Will try the cola either way though might use it to flush through after using acids and as an extra clean through the entire engine.

It’s a frustrating task when the weather is so nice, hopefully I will have her in the water by the weekend just in time for the weather do go down hill ? such is life haha

 

[Andy92]

The confusion would include me, is the cheapest roller cola available likely to be the best stuff for the job ?

 

[Andy92]

Hi Scottie thanks for the help, flow is there so that has to be a good sign just a big difference in volume at the minute, I can get about 5 large syringes full of fluid in the rear jacket and only two or so in the front? Both drains are flowing all be it one much better than the other.

Will the shims be specific to that engine block ?

 

[VicS]

The confusion would include me, is the cheapest roller cola available likely to be the best stuff for the job ?

There really is not a lot of phosphoric acid in Coca Cola. I have seen a figure of 17mg phosphorus / 100ml for regular Coke That works out at only 54 mg H₃PO₄/100ml ie only 0.054%
Phosphoric acid is not such strong acid as hydrochloric acid either

If an HCl based brick cleaner (which contains between 5 and 10% HCl ) does not work a cola is not likely to have any significant effect

 

[VicS]

Hi Scottie thanks for the help, flow is there so that has to be a good sign just a big difference in volume at the minute, I can get about 5 large syringes full of fluid in the rear jacket and only two or so in the front? Both drains are flowing all be it one much better than the other.

Will the shims be specific to that engine block ?

Yes the thickness of the shims are determined during rebuilding but if you are reassembing using the old cylinder blocks you will be able to reuse the existing shims or replace me with new ones of the same thickness if the existing ones are not reusable

The procedure for determining the shim thickness is described in the workshop manual under "Adjusting the compression ratio"

https://www.manualslib.com/manual/1003062/Volvo-Penta-Md1b.html?page=1#manual

 

[Andy92]

Thanks to everyone for the reply’s,

I got some fernox and circulated it through the engine over night, lots of crap came out but still overheating.

So I bought some brick cleaner and did the same and a lot of crap came out including some quite heavy particles. Still overheating

So I bit the bullet took the head off, water jackets were almost solid with crap, I’ve cleaned them out with a rod as best as I can (some I couldn’t shift)

Re assembled and then fired it up first turn of the key but no oil pressure !!

Turns out the oil pump doesn’t self prime so I packed it with Vaseline and the pressure came back, but still overheating on the front cylinder though much better.

I bought an infrared thermometer to monitor the temperatures more scientifically, mostly between 40 and 60 degrees hit with a hot spot at the base of the forward sleeve which reaches 90 degrees !

I decided my issue now may be a reduced flow rather than a complete blockage meaning the front cylinder has overheated before the manifold and thermostat warm up to open the flow.

So I took the thermostat out and it now runs at 40 everywhere, going to live with it like this for a while I think.

Took the boat out and ran the engine for a few hours, then noticed the oil pressure dropped from 40 (p.s.i ?) warm to 20, not sure what’s caused this I’m wondering if the Vaseline has got hot and thinned the oil.

Out of interest does anyone know what pressure these engines should run at ? Maybe it’s time for a new thread haha

Thanks again you lot the helpful advice was really appreciated

 

[TC Tuckton]

Andy92, thank you for starting this thread and reporting back on progress. Sorry I don't know the recommended oil pressure.

Ten years ago I had similar problems with an an MD11C and tried the same techniques as you (but was not brave enough to take the heads off). I do have a couple of hotspots around 90c but they are stable i.e. they don't get much wider under load which suggests the nearby material is conducting heat away effectively to regions with better water flow. I think the cast iron blocks and steel liners can handle that. I do keep an eye on exhaust water flow and temperature. The engine continues to start and run well.

I suspect I will have to take the heads off at some stage. How difficult did you find it?

 

[ghostlymoron]

TC, it's not difficult to remove the heads if you can use a spanner/socket and access is okay. As Vic says you may need different shims to get the compression correct and these are difficult to source on a 40yr old engine.

 

[ghostlymoron]

Correction, shims are available from a number of suppliers.

 

[TC Tuckton]

Ghostlymoron, thanks for the reassurance about removing heads.

 

[Andy92]

Hi TC, that gives me some confidence I think I was becoming overly paranoid about some of the hot spots, couldn’t have run it as it was before I cleaned it out though.

I’m hoping there aren’t any adverse affects of running without a thermostat, I think the cylinder would need an ultrasonic bath or something with the liners out to get it clean enough to run with the thermostat in.

Yeah as Ghostlymoron says it wasn’t difficult at all, I’m fairly practical but I’ve never attempted taking a head off before this and wouldn’t have had the confidence. The guy I bought the boat off offered to help me with it as he had rebuilt the engine in the past, he has been incredibly helpful with loads of things so far. Now I’ve done it I wouldn’t hesitate to do it again.

I got two boxes so I could keep the parts from each cylinder separate

From memory Was essentially,

-starter motor off
-exhaust elbow off
-exhaust manifold off (8bolts)-I re used the gaskets
-rocker covers off (one bolt)
-Rockers off (two bolts and an oil feed union, make a note which cylinder they are from)
-pushrods just pull out (make a note which cylinder and weather they are exhaust/inlet so they go back the same way)
-remove all 6 cylinder head nuts
-the oil feeds to the rockers have to be bent out of the way, I moved it 90 degrees clockwise to allow the head off, bit of a silly design I think. I accidentally loosened one of them. If this happens you simply raise the cylinder up a few inches just prior to re-assembly. Do this with the head back in place but not bolted on and the oil feeds bent back to the correct position, you will see it can be nipped up again where it enters the crank case in the few inches gap you have made by raising the cylinder.
The heads now come off.
I put a rag in the cylinders to stop crap getting in.
I bought new head gaskets from ASAP supplies for 27pounds each I think, I think you could probably get away with re using the old ones but I didn’t want to risk it.
I never disturbed the shins at the base of the cylinder so just put it back and she fired up first turn of the key. You can get them from ASAP supplies and they aren’t very expensive. Seem to be 0.2 and 0.3mm thicknesses so would have just measured the old ones with a micrometer and replaced accordingly.
I avoided removing the cylinders because I didn’t want the hassle of getting the piston back in (I imagine this to be a nightmare but then again I was scared of removing the head at first)

Rodding the crap out was the hardest part and I still didn’t get it all.

Re assembly is a reversal of the process the head nuts must be toqued in the sequence shown in the manual and to the specified torque setting

I think the whole job could be done in a full day

I was convinced it would never work again until I turned the key !!

Hope that helps

 

[Andy92]

Also one more thing I forgot, prior to bolting the heads back up you should loosely install the exhaust manifold with a few bolts finger tight, that way the faces of the exhaust ports on the individual heads will be square to each other and flush to the exhaust manifold

 

[TC Tuckton]

Hi Andy92, thanks for a clear recipe for head removal. Seeing it written down is really useful. Have you considered using a higher temperature thermostat?

Re monitoring hot spots. I plan to plot a 90c contour with a chinagraph pencil on the block at tickover and full load. Up till now it has been an estimate. I recognise there will be errors with the IR thermometer but I hope to reduce these by using a fixed distance (possibly with a 10cm length of wood taped to the end. I know I can't measure between the cylinders, I 'm just looking for a sample site to monitor.

I will continue to monitor exhaust water flow and temperature (like a paranoid hawk...), that's where the vulnerable rubber exhaust hose and plastic muffler are. On the two occasions the engine has overheated in the last 20 years there was a very clear change in engine sound as the temp gauge came up. One occasion was weed blocking the inlet the second was the furred up manifold. If my sample hot spot grows I'll follow your example.