Dexta Diesel Overheating?

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muszeo
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Dexta Diesel Overheating?

Post by muszeo »

We've had our 1962 Dexta Diesel for about three years. Last year she had a head gasket replacement, fluid flushing and oil flushing and filters replacements and she's been running great ever since. Very smooth and plenty of pep.

However, just recently, she's starting cutting out occasionally when run with a mower or chipper load, at high-ish revs for about 30 minutes or more. This is especially true on warm days, less so when it's cold out. I'm concerned that this is an overheating issue as she's had seepage from the radiator cap which is indicative of boiling over. She starts up fine again after cutting out and resting for only 30-60 seconds, which is odd. Sadly the machine has no temperature gauges fitted, these were removed before we took ownership, so I'm flying a bit blind here.

Do you guys think this is a sign of over-heating? If so, what do you think are the likely causes? Water pump? Air in the system? Oil pump or circulation issues? Other than the seepage at the radiator cap she doesn't loose water or oil noticeably.

What else could cause cut outs such as these?

When she's running at lower revs she'll work away for hours without so much as a boo.

Cheers in advance!

Mervyn Spencer
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Re: Dexta Diesel Overheating?

Post by Mervyn Spencer »

A couple of things you may check out firstly, is your radiator clean of debris and secondly check the oil bowl at the bottom of the air filter you may find it full of debris as well. You water pump maybe also in need of replacing and also check the fan belt tension. These are just obvious things that come to mind, I hope it is not something too serious for your sake. Maybe maybe someone else can/will come up with a different idea. Good luck.

muszeo
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Re: Dexta Diesel Overheating?

Post by muszeo »

Thanks Mervyn I'll check the air filter and radiator first and then the water pump and see what comes of that!

Mervyn Spencer
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Re: Dexta Diesel Overheating?

Post by Mervyn Spencer »

I'm holding thumbs for you. :)

fenhayman
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Re: Dexta Diesel Overheating?

Post by fenhayman »

I'm a bit puzzled. If an engine overheats to the extent that the revs drop it's likely that is siezing up. If that happens it won't run properly again and will eventually sieze solid.

If a diesel engine slows down it's either due to too much load or a shortage of fuel or air.
To check for air shortage drop the oil bowl at the bottom of the air cleaner and see if revs pick up. The upper gauzes of an air cleaner can be bunged up even if the oil in the bottom is clear.
Check the fuel flow from the tank. Prolonged running at high revs can cause a fuel shortage if the filter in the tank is partially blocked. Stopping the engine for a few minutes will partially clear it. Last thought -is the fuel tank cap venting properly- fast revs can cause a vacuum in the tank if the cap isn't letting in air which will be released after a short stoppage. Take the cap off and see what happens.

muszeo
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Re: Dexta Diesel Overheating?

Post by muszeo »

Well I sure am glad I asked the question here and didn't persist running it. I took off the radiator to clean it out, and discovered that it had virtually no water in it at the bottom, despite top-ups from the top. Blockage to be sure.

But wait -- there's more.

The bolts at the bottom had corroded through. A previous owner has obviously done a patch-up job with sealant and that has clearly failed, allowing water to slowly escape from underneath the radiator unit.

So it seems very probable that it has been overheating and that the cause is no water circulating.

What amazes me is that she has run at all in this state. I can only hope fingers-crossed that the damage is not that great internally, though I have my doubts. I'll put a new radiator on her and make sure the pump and thermostat are operating correctly and see how it goes. I don't much fancy an engine rebuild right at the moment.

Thanks fenhayman for your advice on the fuel flow and air filter. I'll check those as well! I have had fuel issues in the past that has necessitated loosening the injector nuts, manually pumping the fuel pump and getting fuel to flow. I figured I was unlucky with an air bubble. It never occurred to me that this might be a blockage further up the line, d'oh.

PS. Yikes -- Radiator $475 (NZD -- I'm in NZ). Now I see why the previous owner tried to patch it. Oh well, needs must.

kiwiland dexta
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Re: Dexta Diesel Overheating?

Post by kiwiland dexta »

Have you tried dismantlers for a 2nd hand radiator or looked at re-coring?
There are a few options even here in NZ!
you know it's a classic when people stop to watch.

Bluebilly
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Re: Dexta Diesel Overheating?

Post by Bluebilly »

30-60 seconds is not long for an engine to cool down if it has indeed stopped on overheating. Sounds more like a fuel issue as I had a similar event on my Dexta recently, it just died after having run fairly hard and restarted again fairly soon after. When I looked at the lift pump it was fairly badly worn and I fitted a new one. It now starts easier and runs better. Might be worth a look in that direction too.
1948 E27N
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muszeo
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Re: Dexta Diesel Overheating?

Post by muszeo »

Ok thanks guys, I'll check the fuel system and see if there's an issue there too. I've got a radiator in the post as well. Fingers crossed!

muszeo
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Re: Dexta Diesel Overheating?

Post by muszeo »

Hello again,

Following the above discussion, I've changed the radiator on our Dexta Diesel, cleaned out the air cleaner (and restored it while I was at it) and checked the fuel lines. She starts perfectly and runs smoothly, she's not over-heating and stopping any more as she was. Thanks for your help with this.

However I've noticed now a couple of things that may be off and are worth checking on. A fair amount of steam is coming out of the small copper pipe sticking out of the brass radiator filler cap which I am reading as it's boiling. I've also noticed that the water pipes feeding into the top of the radiator are getting very hot and those at the bottom are absolutely cold, as is the main body of the radiator itself. I would expect a small amount of residual heat going into the engine at the bottom, and the radiator to be warm to touch. Though the hot pipes at the top is not untypical, I am thinking that there is still a circulation problem.

The water pump is pretty corroded on the outside. When I had it apart to fit the radiator I checked the impeller blades were free of dirt with a bit of wire, which they appeared to be, but I couldn't sight them to see if they are damaged.

I have not noticed much in the way of dirt or sludge in the water when I've changed it, so I a hoping it's not an internal blockage.

Any thoughts?

EDIT -- just checking the radiator cap. There's no rubber seal on it, so I think that might be why it's leaking. I'll try fixing that first!

Cheers, M

Dexta J
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Re: Dexta Diesel Overheating?

Post by Dexta J »

Maybe a thermostat? I cooked my David Brown Cropmaster engine because of a rusted thermostat.

fenhayman
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Re: Dexta Diesel Overheating?

Post by fenhayman »

I am no scientist but I understand that water under pressure has a higher boiling point. A proper sealing radiator cap will increase the water pressure and raise the boiling point. That's why we are told not to undo cap when water is hot. Try a new cap

Mervyn Spencer
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Re: Dexta Diesel Overheating?

Post by Mervyn Spencer »

I had an experience with my radiator cap not sealing properly, I think my pressure rating on my original was about 40?? and then changed it to a 70??(can't recall the whether it was psi or what ever). However that did not stop my leak out the overflow at the neck of the filler, what I eventually found was there was a high spot where the rubber seal sat on the brass seat. I sanded it down flush and that was the end my issue. Just a point of interest. I like to believe it is the thermostat that is none functional.
Best of luck.

muszeo
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Re: Dexta Diesel Overheating?

Post by muszeo »

Thanks all for your suggestions and replies. I've managed to resolve this issue, I did replace the cap but still had the same issue. In the end I took out the water pump and the thermostat and found ultimately that the thermostat was at issue. It had jammed itself closed, so water clearly not circulating. I removed the thermostat, to see if it circulated without it, and hey-presto. So, several issues -- radiator, cap and thermostat. It's a wonder it ran! It now runs well and sounds a lot healthier as well. The cap is not bleeding any coolant, so job done!

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