Lemforder Engine Mounts, Serpentine Belts, and Radiator Caps: An Honest Parts FAQ

What I get asked every week

Nine years of buying aftermarket parts for an independent shop means my inbox is roughly 60% the same six questions. They look unrelated — one is about a brand, three are about specific parts, two are about repair jobs — but they tend to turn up on the same car in the same week, so I've been answering them together for a while now.

• Is the Lemforder brand actually trustworthy?
• Are Lemforder engine mounts worth the premium?
• Is rough idle always a mount problem?
• What is a serpentine belt actually for?
• Crankshaft pulley removal — what goes wrong?
• What does a radiator cap do?

Short answers below. Longer ones where they're earned.

Is the Lemforder brand actually trustworthy?

Lemforder shows up as the default name on most of our European chassis quotes — control arms, tie rod ends, ball joints, and engine mounts. It's the one customers already know, usually as 'OE quality, aftermarket price,' and most of the time that reputation holds up.

Here's the part that's actually useful though: brand trust doesn't transfer cleanly between product categories. I stopped trusting brands and started trusting part numbers back in 2019, and I've been better for it.

Lemforder on steering and suspension? I don't hesitate. Engine mounts? Usually solid — but check fitment. In 2021 I ordered 40 Lemforder engine mounts from memory, without running VIN against the catalog. Six of them came back, because the same generation of the same car uses different mounts depending on which engine it left the factory with. That cost us about $1,200 in returns and roughly 10 days of shipping and re-shipping. The parts were fine. The process wasn't.

Are Lemforder engine mounts worth the money over budget alternatives?

For most cars, yes — and here's why it matters more now than it did a decade ago. According to S&P Global Mobility, the average age of vehicles on US roads reached 12.6 years in 2024. Most of what rolls into a shop is an older car being kept alive by its second or third owner.

An engine mount is rubber bonded to metal, sometimes filled with hydraulic fluid, tuned to absorb vibration at a specific frequency. Cheap copies get the geometry right and the rubber compound wrong, and the failure mode is vibration creeping back in around 20,000 miles. Lemforder's hydraulic mounts hold up; we don't see early delamination on the ones that went in with the right torque.

What to look for when you're diagnosing: cracking or separation in the elastomer, dark fluid weeping out of a hydraulic mount, and visible movement under load. Have someone load the drivetrain in drive with the brake held and watch how far the mount deflects.

Real pricing, for reference: in Q4 2023, a hydraulic mount for a European sedan ran roughly $90 to $220 retail depending on the application, against $250 to $400 for the dealer part. Take that with a grain of salt — my price sheet is older than I'd like.

Wait — is a rough idle always a mount problem?

No. And this is the one that cost me.

In 2022 we replaced a full set of engine mounts on a customer's car — upper hydraulic, lower hydraulic, both of them — because of a heavy idle shake. It still shook. The actual cause was a misfire on one cylinder out of six. $600 in parts and most of two days, wasted, because 'rough idle equals worn mount' is a very comfortable thing to believe.

Check in this order: pull codes and check misfire counters, inspect plugs and coils, clean the throttle body, then look at the mounts. Check the transmission mount too — it gets blamed for everything and inspected almost never. And pay attention to when the vibration happens. A shake at idle that disappears under load points at the engine side. A vibration at specific road speeds points at tires or driveline.

What is a serpentine belt actually for?

It's one belt driving everything bolted to the front of your engine: alternator, water pump, power steering pump, air conditioning compressor. On some engines it also drives a supercharger or an auxiliary water pump through the idlers and tensioner.

The important part is how that changed. Cars from the 1990s ran multiple V-belts, one per accessory. If one snapped, you lost one system and could usually limp home. Most modern engines run a single serpentine belt. Lose it and you lose charging, power steering, and, worst of all, coolant circulation. From that moment the temperature gauge is on a clock, and on a lot of engines it's a 30 to 60 second clock.

So the real purpose of a serpentine belt isn't 'keep the accessories working.' It's to keep all of them working from a single failure point, on a belt you should have replaced at 60,000 to 90,000 miles instead of waiting for it to tell you.

Crankshaft pulley removal — what actually goes wrong?

I'll say up front that I stay inside my lane mechanically. Crank pulley work is about where my lane ends, and I only take it when I have the right tools.

1. Assuming the bolt is standard thread. Some engines use a reverse-thread fastener. Torque the wrong direction and you'll round the head before you loosen anything.
2. Hitting it with an impact gun and nothing holding the crank. The bolt spins, the crankshaft spins with it, and the rubber in the damper gets stressed in a way it wasn't designed for. Fast route to a damaged balancer or a weeping rear seal.
3. Reusing a torque-to-yield bolt. Many crank pulley bolts are single-use by design. They're meant to stretch once. Torque them to spec a second time and they won't hold the clamping load.
4. Jamming a screwdriver into the flywheel teeth. I have watched somebody do this. I have also seen what came after.

In 2022 someone tried an impact gun on a crank bolt with no counterhold and rounded the head. $400 in towing and three days of downtime to remove a pulley that should have taken forty minutes.

What does a radiator cap do?

It's a pressure valve, not a lid. Its job is to pressurize the cooling system so the coolant can run hotter than 212°F without boiling. The rule of thumb in cooling system work is that every 1 psi of cap pressure raises the boiling point by roughly 3°F. Most modern systems run 15 to 16 psi caps, which puts the boiling point somewhere above 250°F. Part of the temperature you see on the gauge is bought with that cap.

It contains two valves: a pressure relief valve that opens when system pressure climbs too high, and a vacuum valve. When the engine cools and the coolant contracts, that vacuum valve opens and pulls coolant back in from the expansion tank instead of collapsing a hose or sucking air into the system.

Where it goes wrong in practice is fitment. Swap a 13 psi cap for a 16 psi cap because 'more pressure sounds better' and you'll find the weak point in your cooling system for free — usually a hose or a plastic tank end. A tired cap does the opposite: it opens too early, the system boils over while the car is just sitting at a light, and there's no leak anywhere. It looks like a head gasket problem and it's a $12 part. I replace them rather than test them. They're not expensive enough to be worth doubting.

When should you hand the job to someone else?

The shop that says it can do everything is never the shop that does anything best.

I'll do mounts, belts, and caps, because those are torque-and-spec jobs where a mistake is recoverable. Alignment, engine internals, transmission work — I send customers somewhere else. Not because we can't, but because somebody does that every single day and will do it faster and cheaper than we can.

Same logic on the supply side. Four years ago a vendor walked away from a small piece of a quote and said, 'this isn't our strength — here's who does it better.' We gave them everything else after that.

So if you're comparing suppliers on a Lemforder engine mount or a belt kit, the cheapest answer isn't the lowest number on the quote. It's the supplier who'll tell you when you've picked the wrong part.