# Diesels **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [December 6, 2009, 7:24pm UTC](https://community.cartalk.com/t/diesels/40417 "2009-12-06T19:24:21Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Jeffmw05](https://avatars.discourse-cdn.com/v4/letter/j/74df32/32.png) [@Jeffmw05](https://community.cartalk.com/u/Jeffmw05)\ **Post date:** [December 6, 2009, 7:24pm UTC](https://community.cartalk.com/t/diesels/40417/1 "2009-12-06T19:24:21Z")
A. Why do Diesel engines have to prime for several secs before starting? B. What are glow plugs exactly, what do they have to do with A C. Are all diesels like A? ---
**Author:** ![rripstop](https://avatars.discourse-cdn.com/v4/letter/r/65b543/32.png) [@rripstop](https://community.cartalk.com/u/rripstop)\ **Post date:** [December 6, 2009, 7:34pm UTC](https://community.cartalk.com/t/diesels/40417/2 "2009-12-06T19:34:44Z")
They don’t prime, the glow plugs have to heat up. Glow plugs assist in the combustion on the compression stroke while the engine is cold. A cold engine may not generate enough heat on compression to ignite the fuel and the glow plugs help. I believe there are diesels without glow plugs that alter the injection timing on startup or have higher compression so they don’t need the glow plugs. ---
**Author:** ![Jeffmw05](https://avatars.discourse-cdn.com/v4/letter/j/74df32/32.png) [@Jeffmw05](https://community.cartalk.com/u/Jeffmw05)\ **Post date:** [December 6, 2009, 10:32pm UTC](https://community.cartalk.com/t/diesels/40417/3 "2009-12-06T22:32:23Z")
Neat, thanks ---
**Author:** ![JoeMario](https://avatars.discourse-cdn.com/v4/letter/j/3bc359/32.png) [@JoeMario](https://community.cartalk.com/u/JoeMario)\ **Post date:** [December 6, 2009, 11:49pm UTC](https://community.cartalk.com/t/diesels/40417/4 "2009-12-06T23:49:35Z")
> **[Glowplug](https://en.wikipedia.org/wiki/Glowplug)** > > A glowplug (alternatively spelled as glow plug or glow-plug) is a heating device used to aid starting diesel engines. In cold weather, high speed diesel engines can be difficult to start because the mass of the cylinder block and cylinder head absorb the heat of compression, preventing ignition (which relies on that heat). Pre-chambered engines use small electric heaters (glowplugs) inside the pre-chambers. Direct-injected engines have these glowplugs in the combustion chamber. The glowplug is a ... ---
**Author:** ![Joseph\_E\_Meehan](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/joseph_e_meehan/32/21_2.png) [@Joseph\_E\_Meehan](https://community.cartalk.com/u/Joseph_E_Meehan)\ **Post date:** [December 7, 2009, 12:16pm UTC](https://community.cartalk.com/t/diesels/40417/5 "2009-12-07T12:16:13Z")
“Prime” here may mean having the fuel pump get up to pressure. In any case the instruction to turn the key on until the light goes out (or whatever) before turning the key to the start position is the way to go. Sometimes it helps to turn the key off and back on for a second few seconds when it is very cold. ---
**Author:** ![Loafer](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/loafer/32/28_2.png) [@Loafer](https://community.cartalk.com/u/Loafer)\ **Post date:** [December 7, 2009, 11:46pm UTC](https://community.cartalk.com/t/diesels/40417/6 "2009-12-07T23:46:17Z")
Indirect injection (IDI) diesels use glow plugs for starting, while modern direct injection (DI) diesels do not. All modern (at least since 2007) automotive diesels are direct injection due to the stringent emissions standards and increase in power density and efficiency. DI engines generally have a lower compression ratio than IDI engines.