Diesel engine starting / first start of the day problems

Question

I’m new to the forum, and no mechanic, so please be kind!

Vehicle in question is a 1999 T35 Renault Master 2.5 D.

It has had first start issues since I’ve owned it, with white smoke (un-burnt fuel I’m told) bellowing out of the exhaust when the van finally kicks into life after allowing the glow plugs to warm for 20+ seconds, regardless of ambient temperature. After it’s started once however it’ll start on the button all day long.

Recently I decided to do something about it, so perhaps naively got the glow plugs changed. Now it won’t start at all! Without the help of Easy Start anyway! I now understand that faulty plugs were unlikely the cause of the initial problem.

The glow plugs appear to be all working and the relay appears to also be doing its job and intact (no breaks). The battery is also new and not a suspected cause.

So… I’ve trawled many forums and have a list together but I’m unsure which of these faults are (most) likely to be the cause and which order to try them in, or if there are other solutions I should be investigating. Please help.

• Fuse for glow plugs is damaged or broken

• Glow plugs are giving a false positive reading and are actually not glowing

• Temperature sensor is faulty

• Coolant temperature sensor is faulty

• Issue with starter motor

• Issue with fuel line or pump

Answer 1

Eliminate the obvious first. Your van started with the old glow plugs (although with some effort), but it doesn't start at all with the new ones (without Easy Start--by the way, please don't use any kind of starting fluid on a diesel engine--it can cause serious damage). Can you put the old glow plugs back in and see if it goes back to the way it was?

I suspect either a bad batch of new glow plugs (it happens), the wrong spec glow plugs for the engine, or they were misinstalled (cross threading or not being torqued correctly can cause air leaks, hence poor compression which will keep any diesel from starting even if everything else is perfect).

The fact that letting the glow run for twenty seconds made a difference in starting with the old plugs, suggests that at least some of them are still good. The fact that the first start of the day after that glow period produced a lot of white smoke suggests in turn that some of them are bad. Instead of swapping them around and guessing, measure the current draw between the relay and each plug in turn while turning the ignition to the glow position. You'll need an ammeter with a current scale that reads over 10 amps DC. If you were in the USA I would recommend this multimeter; I don't know what's available where you are. Measuring the resistance of the plugs out of the engine is not a reliable test; if they are open (infinite resistance) it tells you that they're bad, but you can't tell if they're good without testing in situ for a steady high current draw during the glow cycle (peaking at 12-15A or so).

After resolving any issues with the glow system, you can turn your attention to the other candidates you mentioned, which are both more difficult to diagnose, and also unlikely to have coincidentally occurred at the same time as the glow plugs were renewed.

(Addendum: Let us know in the comments how this part went, and I'll try to help with next steps if needed.)

Answer 2

One thing we don't know is the mileage on this vehicle. Because you have been having issues since you got the vehicle, high mileage, or lack of maintenance could be a factor.

I am unfamiliar with this particular vehicle and I may be at a disadvantage, however a diesel is a diesel. The smoke when the engine does finally start (as was stated in another answer) is indicative of unburnt fuel that does not burn in the combustion chamber, enters the exhaust, and once the engine is running the heat from the burnt gases cause it to smoke.

Diesel engines ignite their fuel by compressing the intake air, which creates heat high enough to ignite the fuel. Cold engine, with cold air cannot create enough heat to ignite the fuel, hence the need for glow plugs. They supply added heat, enough to ignite the fuel even when the ambient temperature is low. If there is compression loss this accentuates the problem, especially upon the first start of the day.

Changing the glow plus making it harder (or impossible) to start sounds like, as in another answer the plugs may not be the correct ones for the vehicle. Sometimes older glow plugs will have less resistance in some and not others. What this can cause is some plugs working and getting higher current flow allowing it to heat to a higher temperature. A worn/high mileage engine with marginal compression can be hard to start after it sits overnight, and it takes more heat to get it started.

Checking the voltage, resistance and amperage (current) flow is the first way to check glow plugs. Depending on the type of glow plug, you can have proper resistance, and correct amperage (current) flow, and still have an issue with the plug itself. If it is a "pencil" type it could be heating but not at the tip where it needs to heat to be inside of the combustion chamber. To test them you must have them out of the vehicle where you can see the tip to see that it is actually glowing.

The low compression question seems to be the most reasonable based on the small amount of info we have to work with. I don't know the maintenance that has/has not been done, so this is a possibility. We had several Mercedes that had this same issue. After checking the usual suspects, glow plugs, glow plug relay, starter speed, etc., we checked the valve lash and found that the valves were indeed tight. We adjusted them to specs and the problem went away.

If the valve lash has not been checked/adjusted since you have had the vehicle, I would start there. It's not terribly expensive, and it is a needed and much neglected maintenance item. If that does not fix the problem I would have the compression checked with the engine cold, after sitting overnight, without trying to start it.

Sorry this is so long. A lot of info and possibilities! I hope this helps. I look forward to seeing what you find.