Pre purchase engine inspection.

[haulyfryn]

I am in the process of buying a 1999 Dufour Classic 32 and would like some advice regarding a possible problem with the engine cooling system. The engine is a Volvo MD 2020 and has recently had a new heat exchanger fitted. During an engine inspection I noticed that the exapansion bottle pressure cap was cracked and that there is evidence of water staining around that area. ( I suspect this could be old stains from before the HE was replaced)
The engine was run for a an hour or so during a sea/sail trial and sounded really good with no signs of overheating or signs of any water escaping from the expansion bottle. Should the overheat buzzer sound when the ignition is turned on prior to starting, as this did not happen, or does it only sound with high temperature? It was also noted that the heat exchanger was still quite warm to touch after about an hour or so, is this normal? The exhaust cooling water appeared to be normal with plenty of water being pumped through the system which also has a temperature sensor fitted to the exhaust and appears to be in working. Any advice please.

 

[gregcope]

I am not an engineer.

The alarm should not sound unless you try the alarm test flick switch.

My 2030B does not have an expansion bottle. It vents to atmosphere via a pipe to the bigle.

Sounds like it might have had an overheat event in the past and you are seeing evidence of that, hence the work. Not uncommon on an engine that age.

It should only sound when the temp sensor reaches 100c according to the manual. From experience this is just before the clouds of steam stage (broken alternator bolt, meant the raw water pump stopped).

When running the heat exchanger should feel hot. The exhaust elbow should be warm.

The heat exchanger will feel hot/warm with the engine stopped as the cooling raw water stops with the engine, and heat soaking out of the engine will keep its temp up for quite a while.

Some checks you can do;
- check the elbow temp with engine warm
- check the state of the fresh water/antifreeze should be nearly full / covering the exchanger
- check impellor / how old. A good sign is spares or old ones kept as spares
- check clamps are tight on the rubber boots

It is not uncommon for these engines to have had a new heat exchanger or exhaust elbow.

The heat exchangers can ge blocked with grit/salt. Yearly / bi-yearly cleaning helps.

The elbows can coke up due to running the engines at low revs or lots of short starts that do not get it upto temp.

If you want to go further, get the exhaust elbow off and inspect for carbon build up. A way to test for this is does the engine reach max revs (3400 ish) and does that push the boat to hull speed (ie fast, large bow wave).

To be honest i would expect some evidence of issues in the past, snd if the exchanger has been replaced (££££) this shows someone cared enought to spend on it.

Get a replacement cap and from your description if it runs well for an hour it sounds okay.

 

[haulyfryn]

Thank you very much for your detailed reply. Will certainly have another look a what you have suggested and I am also going to invest in a IR Thermometer as a back up to alarms and instruments.

 

[garvellachs]

Overheating may have compromised the head gasket too - worth checking carefully around the joint for evidence of leakage, and worth checking the oil is not contaminated with coolant nor the expansion bottle getting over-pressured?

 

[haulyfryn]

Thank you for your reply.

 

[langstonelayabout]

I am not an engineer.

My 2030B does not have an expansion bottle. It vents to atmosphere via a pipe to the bigle.

You may not be an engineer but you can certainly spel as well as us!